# State of Arizona Exceptional Event Documentation

for the Event of July 18, 2011, for the

Phoenix PM 10 

# Nonattainment Area

Produced by:

Arizona Department of Environmental Quality

Maricopa County Air Quality Department

Maricopa Association of Governments

Final Report

January 23, 2013

## EXECUTIVE SUMMARY

In 2005, Congress identified a need to account for even ts that result in exceedances of the National

Ambient Air Quality Standards (NAAQS ) that are exceptional in nature 1 

### (e.g., not expected to reoccur or

caused by acts of nature beyond man-made controls). In response, EPA promulgated the Exceptional

Events Rule (EER) to address exceptional events in 40 CFR Pa rts 50 and 51 on March 22, 2007 (72 FR

13560). On May 2, 2011, in an attempt to clarify this rule, EPA released draft guidance documents on the

implementation of the EER to State, tribal and lo cal air agencies for review. Based on numerous

comments EPA received on the May 2011 draft, EPA issu ed a revised draft guidance document in June

2012. The EER allows for states and tribes to “flag” air quality monitoring data as an exceptional event

and exclude those data from use in determinations with respect to exceedances or violations of the

NAAQS, if EPA concurs with the demonstr ation submitted by the flagging agency.

Due to the arid nature of the state, Arizona is high ly susceptible to windblown dust events. These events

are often captured by various air quality monitoring equipment throughout the state, sometimes resulting

in exceedances or violations of the PM10 NAAQS. In the past, the Arizona Department of

Environmental Quality (ADEQ) has submitted exceptiona l event documentation for these events. Due in

part to issues within the EER, obt aining concurrence on these events has been a difficult task. The ADEQ

is now taking a new approach and focusing excepti onal event documentation on ev ents that are believed

to be clear-cut exceptional events that are not controllable by huma n intervention, such as the dust events

that frequently occurred during the monsoon seas on of 2011. This new approach was used for the

exceptional event demonstration submitted in Ma rch 2012 by ADEQ for several PM10 events that

occurred from July 2 – July 8, 2011, in the Phoeni x region. In September 2012, EPA concurred that the

July 2–8, 2011 events were indeed exceptional. As a result, this document is designed to follow the

format used in the July 2–8, 2011 events submission.

This demonstration contains detailed informati on about the windblown dust event that affected the

Phoenix PM10 nonattainment area on July 18, 2011. On that day, eight exceedances of the PM10

NAAQS occurred within the nonattainment area. Add itional exceedances occurred outside of the Phoenix

PM10 nonattainment area on this date, and additional documentation may be submitted as a separate

package at a later time. ADEQ contends that th e exceedances that were measured on July 18, 2011,

within the Phoenix PM10 nonattainment area were the result of natural events that were not reasonably

controllable or preventable. This assessment repor t of the July 18, 2011 dust event was a collaborative

effort involving staff from the Ariz ona Department of Environmental Quality, Maricopa Association of

Governments, Maricopa County Air Quality Department , and Pinal County Air Quality Control District.

Section I of this assessmen t provides a summary of the exceptional event rules and requirements and lays

out how those rules are met with in this specific assessment.

Section II of this assessment introdu ces the conceptual model of the thu nderstorm events that transpired

on July 18, 2011, providing a background narra tive of the exceptional events.

Section III of this assessment provides data summaries a nd time series graphs that help illustrate that the

events of July 18, 2011, produced PM10 concentrations in excess of normal hi storical fluctuations.

1 Section 319 of the Clear Air Act (CAA), as amended by section 6013 of the Safe Accountable Flexible EfficientTransportation Equity Act: A Legacy for Users (SAFE-TEA-LU of 2005), required EPA to propose the Federal Exceptional

Events Rule (EER) no later than March 1, 2006.

### Section IV of this assessment details the existing area control measures and demonstrates that despite the

presence and enforcement of these controls, the event on July 18, 2011, was not reasonably controllable

or preventable.

Section V of this assessment esta blishes a clear causal connection betw een the natural events of July 18,

2011, and the exceedances of the 24-hour PM10 standard at the monitoring stations. The evidence in this

section (and the previous section on hi storical fluctuations) also confir ms that the event in question both

affected air quality and was the result of natural events.

Section VI of this assessment builds upon the demons tration showing a clear causal connection between

the natural events and the exceedances and conclude s there would have been no exceedances on July 18,

2011, but for the presence of the natural events.

Section VII contains conclusions that summarize the excep tional event that occurred on July 18, 2011,

and relates the requirements in the EER to the information within this document.

-ii-

## Table of Contents

I. EXCEPTIONAL EVENT RULE (EER) REQUIREMENTS ........................ 1

Procedural Requirements .................................................................................................... 1

Public notification that event was occurring (40 CFR 50.14(c)(1(i)) ................................ 1

Place informational flag on dat a in AQS (40 CFR 50.14(c)(2)(ii)) .................................... 1

Notify EPA of intent to flag th rough submission of initial event description by July 1 of

calendar year following event (40 CFR 50.14(c)(2)(iii)) .................................................... 1

Document that the public comment process was followed for event documentation (40 CFR

50.14(c)(3)(iv)) .................................................................................................................... 2

Submit demonstration supporting excepti onal event flag (40 CFR 50.14(a)(1-2)) ............ 2

Documentation Requirements ............................................................................................ 2



## II. CONCEPTUAL MODEL ................................................................................. 4

Geographic Setting and Climate ......................................................................................... 4

Geographic Setting of Monitors .......................................................................................... 4

Climate

............................................................................................................................... . 7

Monsoon Season Description and Event Summary .......................................................... 8

Conclusions ......................................................................................................................... 10



## III. HISTORICAL FLUCTUATIONS ............................................................... 14

Regulatory Measures and Control Programs .................................................................. 18

PM10 Rule Effectiveness ................................................................................................... 21

Compliance and Enforcement Activities .......................................................................... 22

Conclusions ......................................................................................................................... 24



## V. CLEAR CAUSAL RELATIONSHIP ............................................................ 25

Introduction ........................................................................................................................ 25

Event – July 18, 2011 ......................................................................................................... 25

Visibility Cameras .............................................................................................................. 33

Conclusion ........................................................................................................................... 33



## VI. “BUT FOR” ANALYSIS .............................................................................. 34

VII. CONCLUSIONS .......................................................................................... 35

Affects Air Quality ............................................................................................................. 35

Natural Event ..................................................................................................................... 35

Summary ............................................................................................................................. 36

-iii-

## List of Figures

Figure 2-1. Phoenix Geographi c Setting and PM10 Monitor Locations (source: EPA AQS

DataMart, NASA MODIS Satellite , Google Earth). PM10 monito r locations are indicated by

the white markers.

............................................................................................................................... ... 5

Figure 2-2. Drainage Syst em of Phoenix, Arizona. ......................................................................................6

Figure 2-3. Phoenix Monthly Precipitation (top) and Maxi mum Temperature (bottom)

Climatology (source: National Weather Service) ..................................................................................7

Figure 2-4. Cross-section of a thunderstorm creating an outflow boundary and haboob (Source:

Desert Meteorology. Thomas T. Warner. 2004.) ...................................................................................9

Figure 2-5. U.S. Drought Monitor an alysis released during the tim e period of the exceedances

described in this report. ........................................................................................................................11

Figure 2-6. Timeline of PM10 concen trations at monitors in the Phoenix area before, during and

after the July 18, 2011 event ................................................................................................................12

Figure 3-1. Plot of daily hour ly maximum PM10 concentrations (2007 – 2011) at the South

Phoenix monitoring site. ......................................................................................................................14

Figure 3-2. Plot of 24-hour av erage PM10 concentrations (20 07 – 2011) at the South Phoenix

monitoring site.

............................................................................................................................... ..... 15

Figure 3-3. Plot of daily hour ly maximum PM10 concentrations (2007 – 2011) at the Buckeye

monitoring site.

............................................................................................................................... ..... 16

Figure 3-4. Plot of 24-hour average PM10 concentrations (2007 – 2011) at the Buckeye

monitoring site.

............................................................................................................................... ..... 17

Figure 4-1. Timeline of Maricopa Count y Fugitive Dust Rules and Ordinances. ......................................22

Figure 5-1. Satellite imagery showing strong st orms developing and dissi pating over Pinal County

and areas to the southeast of P hoenix. These storms are believed to have been responsible for

the thunderstorm outflow boundary that caused PM10 exceedances in Maricopa and Pinal

counties on July 18. ..............................................................................................................................26

Figure 5-2. Phoenix nonattainment area PM10 monito r readings and Sky Harbor wind speed and

visibility for July 18, 2011. ..................................................................................................................28

Figure 5-3. Pinal County PM10 monito r readings and Casa Grande wind speed and visibility for

July 18, 2011.

............................................................................................................................... ........ 29

-iv-

## List of Tables

Table 2-1. Summary of Statewide PM10 Measurements for July 18, 2011. ..............................................13

Table 4-1. Rules and Ordinances Regulating Particulate Matter Emissions in Maricopa County .............19

Table 4-2. Pinal County Rules Regulating Existin g and New Non-point Sources in Pinal County ............20

Table 4-3. Pinal County Rules Regulating Fugitive Dust in Pinal County Portion of Maricopa

County PM10 Nonattainment Area ......................................................................................................20

-v-

### -vi

## List of Appendices

Appendix A – 5-year Historical Fluctuation Graphs for the Phoe nix Nonattainment Area PM10 Sites

Appendix B – ADEQ Forecast Products for P hoenix, Maricopa County, and Pinal County

Appendix C – Notice of Public Comment Period

Appendix D – National Weather Servic e Forecasts, Warnings, and Alerts

## I. EXCEPTIONAL EVENT RU LE (EER) REQUIREMENTS

In addition to the technical requirements that are c ontained within the EER, proc edural requirements must

be met in order for EPA to concur with the flagged ai r quality monitoring data. This section of the report

lays out the requirements of the EER and associated guidance, and disc usses how the Arizona Department

of Environmental Quality (ADEQ) addressed those requirements.

Procedural Requirements

This section presents a review of the procedur al requirements of the EER as required by 40 CFR 50.14

( Treatment of Air Quality Monitoring Data Influenced by Exceptional Events ) and explains how ADEQ

fulfills them. The Federal EER requirements include notifying the public that an event was occurring,

placing informational flags on data in EPA’s Air Qua lity System (AQS), notifying EPA of the intent to

flag through submission of initial event descriptio n, documenting that the public comment process was

followed, and submitting a demonstration supporting th e exceptional events flag. ADEQ has addressed

all of these procedural and documentation requirements.

Public notification that event was occurring (40 CFR 50.1 4(c)(1(i))

ADEQ issued a Dust Control Action Forecast and an Ensemble Forecast for the Greater Phoenix area

advising citizens of the potential for high winds a nd blowing dust on July 18, 2011. More information on

ADEQ’s forecasting program can be found in Section IV. The forecast products that were issued for

July 18, 2011, are included in Appendix B.

Place informational flag on data in AQS (40 CFR 50.14(c)(2)(ii))

ADEQ and other operating agencies in Arizona subm it da ta into EPA’s AQS. Data from both filter-based

and continuous monitors operated in Arizona are submitted to AQS.

When ADEQ and/or another agency operating monitors in Arizona suspect s that data may be influenced

by an exceptional event, ADEQ and/or the other opera ting agency expedites analysis of the filters

collected from the potentially affected filter-based ai r monitoring instruments, quality assures the results,

and submits the data into AQS. ADEQ and/or other operating agencies also submit data from continuous

monitors into AQS after quality assurance is complete.

If ADEQ and/or the operating agency have determined a potential exists that the monitor reading has been

influenced by an exceptional event, a preliminary fl ag is submitted for the measurement in the AQS. The

data are not official until they unde rgo more thorough quality assurance and quality control, leading to

certification by May 1 of the year following the ca lendar year in which the data were collected

(40 CFR 58.15(a)(2)). The presence of the flag can be confirmed in AQS.

Notify EPA of intent to flag through submission of in itial eve nt description by July 1 of calendar year

following event (40 CFR 50.14(c)(2)(iii))

ADEQ submitted notice to EPA on August 29, 2012, listing all days from calendar year 2011 that ADEQ

intended to analyze under the Exce ptional Events Rule and notifying the EPA of which PM10 data were

flagged in AQS. Exceedances that occurred on July 18, 2011, within the Phoenix PM10 nonattainment

area were included on that list. Th is report serves as the demonstra tion supporting the flagging of these

data.

-1-

### On July 18, 2011, eight monitoring sites within the boundaries of the Phoenix PM10 nonattainment area

exceeded th e 24-hour PM10 standard during the hi gh wind event that occurred during the late

afternoon/evening hours. The PM10 monitors impact ed were the Buckeye, Central Phoenix, Durango

Complex, Dysart, Greenwood, South Phoenix, West 43 rd 

### , and West Phoenix monitors operated by

Maricopa County Air Qualit y Department (MCAQD).

Document that the public comment proce ss was followed for event docu mentation (40 CFR

50.14(c)(3)(iv))

ADEQ posted this assessment report on the ADEQ webpa ge and placed a hardcopy of the report in the

ADEQ Records Management Center for public revi ew. ADEQ opened a 30-day public comment period

on December 3, 2012. A copy of the public notice certification, along with any comments received, will

be submitted to EPA, consistent with the requirements of 40 CFR 50.14(c)(3)(iv). See Appendix D for a

copy of the affidavit of public notice.

Submit demonstration supporting exceptional event flag (40 CFR 50.14(a)(1-2))

At the close of the comment period, and after ADEQ has had the opportunity to consider any com ments

submitted on this document, ADEQ will submit this document, the comments received, and ADEQ’s

responses to those comments to EPA Region IX headqua rters in San Francisco, California. The deadline

for the submittal of this demons tration package is September 30, 2014.

Documentation Requirements

Section 50.14(c)(3)(iii) of the EER states that in order to jus tify excluding air quali ty monitoring data,

evidence must be provided for the following elements:

a. The event satisfies the criteria se t forth in 40 CFR 501(j) that:

(1) the event affected air quality,

(2) the event was not reasonably cont rollable or preventable, and

(3) the event was caused by human activity unlikely to recur in a particul ar location or was a

natural event;

b. There is a clear causal relations hip between the measurement under consideration an d the event;

c. The event is associated with a measured concentr ation in excess of normal historical fluctuations;

and

d. There would have been no exceedance or violation but for the event.

Section II of this assessme nt introduces the conceptual model of the high wind event that transpired on

July 18, 2011, providing a backgrou nd narrative of the excep tional events and an overall explanation on

how “the event affected air quality.” Further eviden ce that “the event affected air quality” is provided in

Section V. Sections II and V also provide evidence that the event was a natural event.

Section IV of this assessment details the existing area control measures and demonstrates that despite the

presence and enforcement of these controls, the event on July 18, 2011, was not reasonably controllable

or preventable.

Section V of this assessment esta blishes a clear causal connection betw een the natural events of July 18,

2011 and the exceedances of the 24-hour PM10 standard at the monitoring stations. The evidence in this

section (and the previous section on hi storical fluctuations) also confirms that the events in question both

affected air quality and were the result of natural events.

-2-

### Section III o f this assessment provides data summaries a nd time series graphs that help illustrate that the

event on July 18, 2011, produced PM10 concentrations in excess of normal hist orical fluctuations.

Section VI of this assessment builds upon the demons tration showing a clear causal connection between

the natural events and the exceedances and conclude s there would have been no exceedances on July 18,

2011, but for the presence of the natural events.

-3-

## II. CONCEPTUAL MODEL

Geographic Setting and Climate

This section describes the geographic and climatic setting of the monitors.

Geographic Setting of Monitors

Phoenix is located in the Salt R ive r Valley in south-central Arizona. It lies at a mean elevation of 1,090

feet above mean sea level (m sl) in the northeastern pa rt of the Sonoran Desert. Other than the mountains

in and around the city, the topography of Phoenix is ge nerally flat. The Phoenix area is surrounded by the

McDowell Mountains (~4,200 ft msl) to the northeast, the foothills of the Bradshaw (~7,900 ft msl) and

Mazataal (~7,900 ft msl) ranges to the north, the Wh ite Tank Mountains (~4,500 ft msl) to the west, the

Sierra Estrella (~4,450 ft msl) to th e southwest, and the Superstition Mo untains (~5,000 ft msl) far to the

east. Within the City are the Phoenix Mountains (~2,600 ft msl) and South Mountain (~2,600 ft msl).

Current development is pushing north, west, and south into Pinal County. The Phoenix metropolitan area

contains a fairly dense network of PM10 monitors throughout the area, with a much less dense network of

monitors located throughout the rest of the state. Figure 2-1 s hows the general geographic setting of

Phoenix, as well as the locations of PM10 monitors thr oughout the state. It should be noted that some of

the monitors shown in Figure 2-1 are filter-based mon itors; therefore, monitoring data from all locations

may be available only for select days (i.e., 1-in-6 run days).

-4-

### Figure 2-1. Phoenix Geographic Setting and PM10 Monito r Locations (source: EPA AQS DataMart,

NASA MODIS Satellite, Google Eart h). PM10 monitor locations ar e indicated by the white markers.

Figure 2-2 depicts the drainage system s or watersheds for the State of Arizona. Many of the rivers that

form Arizona’s drainage system are dry for most of th e year and, consequently, are sources of silt and fine

soils that become suspended and add to regional PM 10 loadings during high wind events. Much of this

alluvial matter and fine soil is deposited in the lo w lying areas of central a nd southern Arizona, with

larger depositional areas focused in and ar ound the confluences of dry river channels.

-5-

### Figure 2-2. Drainage System of Phoenix, Arizona.

-6-

### Climate

Phoenix has an arid climate, with very hot summers and temperate winters. The average summer high

temperature is among the hottest of any populated area in the United States. The temperature reaches or

exceeds 100oF an average of 110 days during the year and highs top 110oF an average of 18 days during

the year. Phoenix receives an average of 7.66 inches of rain per year.

As shown in Figure 2-3, precipitation is sparse during the first part of the summer, but the influx of

monsoonal moisture, which generally begins in early Ju ly and lasts until mid-Sept ember, raises humidity

levels and can cause heavy localized precipitation and flooding. Although thunderstorms are possible at

any time of the year, they are most common during the monsoon season from July to mid-September as

humid air is advected from the Gulf of California, Gulf of Mexico, a nd large thunderstorm complexes that

form over the Sierra Madre Occidental Mountains in Mexico. This influx of moisture, combined with

intense solar heating, often creates a very unstable environment that is ripe for thunderstorm development.

These thunderstorms can bring strong winds and blow ing dust, large hail, and heavy rain. Dust storms

associated with these thunderstorms typically occur in the early part of the monsoon season (July/August)

before soaking rains help keep soil particles bound to one another. However, depending on the amount of

precipitation received duri ng the monsoon season, extremely hot temp eratures act to dry out the surface

quickly, and dust storms can occur at any time. During the December through March period, winter

storms moving inland from the Pacific Ocean can pr oduce significant rains throughout Arizona. This

December–March time period and the July–August time peri od are typically the wettest parts of the year.

Meanwhile, a distinct dry season occurs from April through June for the Phoenix area and the rest of

Arizona. While these weather patter ns describe the general climatology for the Phoenix area over a long

period of time, Phoenix and the entire state of Arizona are also pr one to a high degree of variability in

these weather patterns from year to year.

Figure 2-3. Phoenix Monthly Precipitati on (top) and Maximum Temper ature (bottom) Climatology

(source: National Weather Service)

-7-

### Monsoon Season Description and Event Summary

A multi-day period, including the event day of July 18, 2011, was characterized by monsoonal

thunderstorm activity throughout Arizona . The North American Monsoon is a shift in wind patterns in

the summer that occurs as Mexico and the southwes t U.S. warm under intense solar heating. As this

happens, low level moisture is trans ported primarily from the Gulf of California and easte rn Pacific Ocean

into the southwestern U.S. The Gulf of California, a narrow body of water surrounded by mountains, is

particularly important for low-leve l moisture transport into Arizona and Sonora. Mid- and upper-level

moisture is also transported into the region, mainly fr om the Gulf of Mexico by easterly winds aloft. This

combination causes a distinct rainy season over large portions of western North America, which develops

rather quickly and sometimes dramatically. Rain fall during the monsoon is not continuous and varies

considerably, depending on a variety of factors. There are usually distinct “burst” periods of heavy rain

during the monsoon, and “break” periods with little or no rain. Even during active monsoon periods,

some areas can go without receiving any significant precipitation while other nearby areas experience

heavy rains and flooding.

The thunderstorm activity in Arizona on July 18 was ac tive in and around the dese rt areas of central and

southern Arizona and northern Mexi co. These thunderstorms did not re sult in much preci pitation for the

Phoenix area, but many of the storms were severe in nature and caused many dust-carrying outflow

boundaries, the most significant of which propagated into the Phoenix area in the late afternoon.

Downdrafts associated with heavy precipitation from thunderstorms or from collapsing thunderstorms can

end up producing what are called downbursts, or some times more concentrated and severe microbursts,

which are rapidly descendi ng bursts of air that come through the thunderstorms. These downward bursts

of air hit the ground and then disper se away from the storms as areas of outflow. These outflow

boundaries from the thunderstorms can kick up larg e areas of dust, sometimes called haboobs, and

transport that dust for long di stances from the initiating t hunderstorms (see Figure 2-4).

The active monsoon occurring on July 18 led to numerous t hunderstorms and thunderstorm outflows that

produced blowing dust in many parts of Arizona, including the Phoenix Me tropolitan area. The

windblown dust event produced eight PM10 exceedan ces in the Phoenix PM10 nonattainment area on

July 18. The event was primarily driven by stro ng outflows from severe thunderstorms producing wind

gusts from one prominent direction. The July 18 th 

### event was a widespread dust event with mostly southsoutheasterly winds transporting dust from the desert areas of Pinal County into the central and western

side of the Phoenix region. Further detail s on the event can be found in Section V.

-8-

### Figure 2-4. Cross-section of a thunderstorm creating an outflow boundary and haboob (Source: Desert

Meteorology. Thomas T. Warner. 2004.)

The nature of these monsoonal dust events is such that specific source areas are difficult to determine, as

outflow from thunderstorms can carry dust over vast distances encompassing many source areas. Because

of this, it is more appropriate to speak of general source regions fo r these monsoonal dust storms, which

typically are identified based upon the locations of the thunderstorms that are believed to have created the

dust generating and carrying outflow winds. A vast majority of the PM10 impacting the Phoenix area

from thunderstorm-driven high winds on July 18 orig inated outside of the Phoenix PM10 nonattainment

area. The contributing source region s to the dust event were somewhat widespread, but the majority of

the PM that was transported into Maricopa County likely came from areas within Pinal County to the

south and southeast of Maricopa County. Other pote ntial source contributors to the PM10 events were

areas in northern Pima County and so utheastern and southern Maricopa County. The exact origin of the

PM sources is often difficult to determine due to the less dense monitoring networks in the general source

area.

Another important factor that le d to these significant dust storms was the on-going drought across the

region. The most recent U.S. Drought Monitor placed the area between Tucson and Phoenix, the primary

dust source region for winds out of the southeast, in D1 (Moderate) to D3 (Extreme) drought (see

Figure 2-5). Rainfall in Phoeni x since October 1, 2010, had been 55% of normal, and only 44% of

normal since January 1, 2011 (see the Daily Climate Report for July 18 in Appendix D). For additional

information pertaining to the 2011 monsoon season in Ar izona, see the news media web links provided

below.

2011 Monsoon Season Summary and Review  http://bcove.me/krh3qk29

-9-

### -10- This video contains information about the m onsoon season, the formation of dust storms in

Arizona, and the uniqueness of the 2011 monsoon season.

2011 Monsoon Season Review 2  http://bcove.me/tc6otk0h

This video contains information about the 2011 monsoon season, focusing on the large

number of dust storms that occurred, and a discussion of why there were so many dust

storms in 2011.

The abnormally dry conditions that were in place dur ing the early part of the monsoon season (which

persisted throughout the duration of the monsoon season) resulted in a la rge fetch of soils that were

vulnerable to particulate suspension. The thundersto rm outflow boundaries that affected Maricopa and

Pinal counties on July 18 resulted in very little rain fall throughout south-centr al Arizona, but the high

winds associated with the outflows di d transport moderate to very high le vels of particulate concentrations

into the Phoenix area. A timeline summarizing the July 18 event can be seen in Figure 2-6. This figure

shows hourly PM10 concentrations for a three-day period around, and including, the event day. During

the 24 hours prior to the event, there were low PM10 concentrations across the Phoenix region for much

of the day, but late afternoon thunderstorms produced weak outflows and modera te winds that caused a

one hour spike in PM10 concentrations around 11 p.m., but the spike was not high enough at any

monitoring sites to cause an exceedan ce of the 24-hour standard. On the event day, the figure shows low

PM10 concentrations during the day and then very high PM10 concentrations during the evening hours

when the thunderstorm outflows trav eled through the Phoenix area. Lastly, the figure shows that PM10

concentrations dropped back down to low levels dur ing the 24 hours after the event, indicating that

without the impacts of the thunderstorm outflows, PM10 concentrations at all sites in the Phoenix PM10

nonattainment area July 18, 2011, would have be en below the 24-hour average PM10 exceedance

threshold of 150 μg/m 3



### .

Following Figure 2-6, Table 2-1 details the PM10 24- hour average concentrations, the daily maximum

hourly concentrations and the time at which they occurred, and the flag given to the data in EPA’s AQS

for all PM10 monitoring sites in Arizona for the event day.

Conclusions

This Conceptual Model was created to provide a basic description of the general climate and weather

patterns that led to the active thunderstorm period on July 18 a nd produced the dust storms and eight

PM10 exceedances in the Phoenix PM10 nonattainment area during the one-day episode. A more

detailed analysis of the windblown dus t event is included in Section V, where a demonstration of the clear

causal connection between the uncontrollable natu ral events and PM10 exceedances is prese nted.Figure 2-5.U.S. Drought Monitor analysisreleased during thetime period of the exceedances described in this report.-11-Figure 2-6.Timeline of PM10 concentrations at monitors in the Phoenix area before,during and after the July 18, 2011 event-12-

### July 18, 2011

Table 2-1. Summary of Statewide PM10 Measurements for July 18, 2011.

Monitor Monitor

Type Operator AQS Monitor ID 24-hr Avg

PM10

(μg/m 3 ) 1-hr Max

PM10

(μg/m 3 ) Max

Time AQS

Qualifier

Flag

Apache County

N/A TEOM WMAT 04-001-1003-81102-1 11 33 1300

Coconino County

N/A TEOM NN 04-005-1237-81102-1 15 31 0200

Gila County

Hayden Old Jail TEOM ADEQ 04-007-1001-81102-3 24 93 1300

Maricopa County

Buckeye TEOM MC 04-013-4011-81102-1 196 1665 1800 RJ

Central Phoenix TEOM MC 04-013-3002-81102-4 210 2056 1800 RJ

Durango Complex TEOM MC 04-013-9812-81102-1 267 1859 1800 RJ

Dysart TEOM MC 04-013-4010-81102-1 163 1008 0000 RJ

Fort McDowell/Yuma Frank TEOM FMIR 04-013-5100-8112-1 32 N/A N/A

Glendale TEOM MC 04-013-2001-81102-1 141 862 1800

Greenwood TEOM MC 04-013-3010-81102-1 208 1549 1800 RJ

Higley TEOM MC 04-013-4006-81102-1 104 937 1700

JLG Supersite BAM ADEQ 04-013-9997-81102-3 125 826 2100 IJ, EH

JLG Supersite TEOM ADEQ 04-013-9997-81102-4 151 1383 1800 IJ

South Phoenix TEOM MC 04-013-4003-81102-1 303 2861 1800 RJ

West Chandler TEOM MC 04-013-4004-81102-1 126 696 1900

West Forty Third TEOM MC 04-013-4009-81102-1 244 1515 1800 RJ

West Phoenix TEOM MC 04-013-0019-81102-1 159 908 2100 RJ

Zuni Hills TEOM MC 04-013-4016-81102-1 100 441 2300

Navajo County

N/A TEOM WMAT 04-017-1002-81102-1 11 30 1300

Pima County

Ajo TEOM ADEQ 04-019-0001-81102-3 27 95 2300

Geronimo BAM PCDEQ 04-019-1113-81102-1 15 57 1400

Green Valley BAM PCDEQ 04-019-1030-81102-1 12 47 1300

Orange Grove FRM PCDEQ 04-019-0011-81102-2 14 N/A N/A

Rillito TEOM ADEQ 04-019-0020-81102-3 43 151 1400

South Tucson FRM PCDEQ 04-019-1001-81102-1 18 N/A N/A

Pinal County

Apache Junction Fire Stn. TEOM PCAQCD 04-021-3002-81102-3 N/A N/A N/A

Casa Grande Downtown TEOM PCAQCD 04-021-0001-81102-3 219 2919 1600 RJ

Combs School TEOM PCAQCD 04-021-3009-81102-3 66 405 1500

Cowtown TEOM PCAQCD 04-021-3013-81102-3 1638 24976 1700 RJ

Maricopa TEOM PCAQCD 04-021-3010-81102-3 531 9756 1700 RJ

Pinal County Housing TEOM PCAQCD 04-021-3011-81102-3 271 3088 1600 RJ

Stanfield TEOM PCAQCD 04-021-3008-81102-3 567 9716 1600 RJ

Santa Cruz County

Nogales Post Office BAM ADEQ 04-023-0004-81102-3 13 28 1600

Yuma County

Yuma Supersite TEOM ADEQ 04-027-8011-81102-3 22 73 0700

Operator Abbreviations: MC – Marico pa County Air Quality Department

PCAQCD – Pinal County Ai r Quality Control District

ADEQ – Arizona Department of Environmental Quality

FMIR – Fort McDowell Indian Reservation

NN – Navajo Nation, AZ, NM, UT

PCDEQ – Pima County Department of Environmental Quality

SRP-MIC – Salt River Pima-Maricopa Indian Community of Salt River Reservation, AZ

WMAT – White Mountain Apache Tribe of Fort Apache Reservation, AZ



### -13-

## III. HISTORICAL FLUCTUATIONS

The PM10 concentrations measured across much of Maricopa County on July 18, 2011, were some of the

highest hourly and 24-hour averages m easured over the last five years. Time series plots of the 24-hour

PM10 concentrations for the period January 1, 20 07, through December 31, 2011, were created for all

PM10 monitors in the Phoenix PM10 nonattainment area. Additionally, time seri es plots of the daily

maximum hourly average PM10 concentrations were created for two monitors in Maricopa County.

These two additional plots were created to provide a deeper understanding of the magnitude of short-term

particulate concentrations and their contri bution to PM10 exceedances in the Phoenix PM10

nonattainment area. Time series plots for two mon itoring sites (South Phoenix and Buckeye) are included

within this section, while the remaining 24-hour averag e plots are available in Appendix A. The South

Phoenix monitor was selected because of its central location in relation to all monitors in Maricopa

County and it was the most severely impacted site during the July 18 windblown dust event. The

Buckeye monitor was selected because it is represen tative of western Maricopa County, an area of the

region frequently impacted by dust storms caused by t hunderstorm outflow events. The graphs below and

in Appendix A show that the July 18 event was in the t op five most extreme events of the last five years

for multiple sites.

Figure 3-1. Plot of daily hourly m aximum PM10 concen trations (2007 – 2011) at the South Phoenix

monitoring site.

-14-

### Figure 3-1 shows the daily m aximum hourly averages from the South Phoenix PM10 monitor. The plot

shows that the July 18 th 

### hourly average of 2861 μ g/m 3 

### was the third highest hourly PM10 concentration

recorded in the last five years. The plot also shows that the maxi mum hourly average was greater than

that observed during the July 5, 2011 haboob event which recently received EPA concurrence. The

hourly average concentrations from this event were surpassed only by two additional dust storms that

occurred in August and September 2011, another indi cation of the severity of the 2011 monsoon season.

It is also clear that the most si gnificant hourly average PM10 concentrat ions at the Sout h Phoenix monitor

typically occur during the July th rough September time frame, a period during which the monsoon season

is most active and the Phoenix region is frequently impacted by haboob events.

Figure 3-2 shows the daily 24-hour averages from the South Phoenix PM10 monitor and indicates that the

July 18 th 

### event produced the third highest 24-hour average PM10 concentration measured in the last five

years. Similar to haboob events that occurred on the same date in 2009, during the first week of July

2011, and during the last week of August 2011, the July 18 event experienced PM10 concentrations that

were well above the 24-hour exceedance threshold.

Figure 3-2. Plot of 24-hour average PM10 concentrations (2007 – 2011) at the South Phoenix m onitoring

site.

Figures 3-3 and 3-4 provide an hist orical look at the daily maximum hourly averages and daily 24-hour

averaged PM10 concentrations from the Buckeye monito r. The plots also show that the maximum hourly

concentration and exceedance measured at the Buck ley monitor on July 18 was among the nine highest

PM10 concentrations measured over the last five years. As was the case for the South Phoenix monitor,

-15-

### the m ost significant hourly average PM10 concentrati ons at the Buckeye monitor typically occur during

the July through September time frame, a period duri ng which the monsoon season is most active and the

Phoenix region is frequently impacted by haboob events.

Figure 3-3. Plot of daily hourly m aximum PM10 con centrations (2007 – 2011) at the Buckeye

monitoring site.

-16-

### Figure 3-4. Plot of 24-hour average PM10 concentrations (2007 – 2011) at the Buckeye m onitoring site.

The plots within this section provi de an historical perspective of PM10 concentrations since 2007. These

plots, along with those in Appendix A, show that the haboob event that occurred on July 18, 2011,

resulted in one of top ten highest 24-hour average PM10 concentrations seen in the last five years. This

equates to PM10 concen trations in the 99.5 th 

### percentile when compared to hist oric data. In the case of the

Greenwood, South Phoenix, and Durango monitoring site s, the 24-hour averaged PM10 concentrations

measured on July 18 were in the top five highest c oncentrations observed during the last five years.

While the PM10 concentrations th at were measured on July 18 th 

### were extreme in many cases, the plots

also show that similar events are not uncommon during the monsoon s eason. As documented in several

published journals and academic text books, haboobs generated from thunderstorm outflow boundaries

are a phenomenon that Arizona deals with every year, some years more so than others, namely in 2007,

2009, and 2011.

-17-

## IV. NOT REASONABLY CONT ROLLABLE OR PREVENTABLE

Section 50.1(j) of Title 40 CFR Part 50 requires that an event must be “not reasonably controllable or

preventable” in order to be define d as an exceptional event. This requirement is met by demonstrating

that despite reasonable control measures in pl ace within Maricopa County and the Phoenix PM10

nonattainment area, high wind conditions overwhelmed all reasonably available controls. The event

occurring on July 18, 2011, was dire ctly related to strong and gusty winds generated by thunderstorm

outflow boundaries. The strong winds overwhelmed a ll reasonably available co ntrols, and were also

responsible for transporting PM into the Phoenix PM10 nonattainment area from areas outside of the

nonattainment area. As explained in the conceptu al model, downdrafts from collapsing thunderstorms

produce outflow boundaries that contai n gusty, turbulent wakes that rais e dust from the desert surfaces

that can be as wide as 100 miles in severe cases. As shown in Section V, the source region for all of the

dominant thunderstorm outflows a nd associated transported dust on July 18, 2011, generally came from

areas outside of the Phoenix PM10 nonattainment area—primarily from th e deserts of Pinal, Pima, and

southern Maricopa counties. Wh ile it is likely that some dus t was generated within the PM10

nonattainment area as gusts from the thunderstorm outflows passed through the area, the amount of dust

generated locally was easily ove rwhelmed by, and largely unnoticea ble as compared to, the dust

transported in from the source region s of the thunderstorm outflows. St rict controls on local sources of

fugitive dust were in place and enforced on July 18, 2011, but were not capable of controlling transported

dust and PM10 raised by the gusty and tur bulent thunderstorm outfl ows on these dates.

The following sections describe the BACM- and MS M-level PM10 control measures in place July 18,

2011, and the robustness of the programs designed to enforce these measures. Pro-active response and

analysis of each event as it is occurring verify the uncontrollable nature of each event, while inspections

of local sources performed before, during, and afte r the July 18, 2011 event confirmed that no unusual

anthropogenic PM10-producing activities occu rred in Maricopa County, the Phoenix PM10

nonattainment area, or the local area s surrounding the exceeding monitors.

Regulatory Measures and Control Programs

ADEQ and MCAQD are responsible for implementing re gulatory measures to control emissions from

agricultural sources, stationary sources, fugitive dus t sources, and open burning within Maricopa County.

Three major programs provide or contribute to air pollution control measures for the Greater Phoenix

area:

1. ADEQ’s Agricultural Best Mana gement Program (AgBMP);

2. Maricopa County’s Inspection and Compliance Program; and

3. ADEQ’s Air Quality Forecasting Program.

Specifically, ADEQ is responsible for compliance assi stance and enforcement of Agricultural Best

Management Practices developed by the Governor’s Ag ricultural Best Management Practices Committee,

while MCAQD is responsible for compliance assura nce for all other significant sources of PM10

emissions. In addition to routine inspections and in spections driven by complaints, inspections are often

increased when (1) ADEQ forecasters issue a High Risk for the Maricopa County Dust Control Forecast,

(2) ADEQ forecasters issue a High Pollution Advisory, or (3) near-real-time monitoring data indicate

unique activity via high PM concentrations. Th e forecasting program a nd inspection/compliance

programs work together so that reso urces can be best utili zed during days that ar e of greatest risk for

elevated PM emissions.

-18-

### On July 25, 2002, EPA took initial action to finalize approval of the Best Av ailable Control Measure

(BACM) and the Most S tringent Measure (MSM) demons trations in the Serious Area PM10 plan for the

Maricopa County portion of the metropolitan Phoe nix PM10 nonattainment area (67 FR 48718). These

BACM and MSM demonstrations were again ap proved by EPA on July 14, 2006 (71 FR 43979). The

Agricultural Best Management Practices General Perm it rule and related definitions have been approved

into the Arizona Administrative Co de as R18-2-610 and R18-2-611 pursu ant to Arizona Revised Statutes

§ 49-457. 2 

### Maricopa County regulations of PM10 emissions are listed in Table 4-1.

Table 4-1. Rules and Ordinances Regulating Pa rticulate Matter Emissions in Maricopa County

Rule/Ordinance Number

& Title Description

Rule 300: Visible

Emissions Establishes standards for vi sible emissions and opacity.

Rule 310: Fugitive Dust

from Dust-Generating

Operations Establishes limits for the emissions of particulate matter into the

ambient air from any property, operations, or activity that may

serve as a fugitive dust source

Rule 310.01: Fugitive Dust

from Non-Traditional

Sources of Fugitive Dust Establishes limits for the emissions of particulate matter into the

ambient air from open areas, vacant lots, unpaved parking lots,

and unpaved roadways that are not regulated by Rule 310 and

that are not required to have ei ther a permit or a dust control

plan

Rule 311: Particulate

Matter from Process

Industries Establishes emission rates based on process weight applicable to

any affected operations not subject to Rule 316.

Rule 312: Abrasive

Blasting Establishes limits for particulate emissions from abrasive

blasting operations

Rule 314: Open Outdoor

Fires and Indoor Fireplaces

at Commercial and

Institutional Establishments Establishes limits for the emissions of air contaminants

produced from open burning

Rule 316: Nonmetallic

Mineral Processing Establishes limits for the emissions of particulate matter into the

ambient air from any nonmetallic mining operation or rock

product processing plant

Rule 317:

Hospital/Medical/

Infectious Waste

Incinerators Establishes limits for the emi ssions of air pollutants from

medical waste incinerators

Rule 322: Power Plant

Operations Establishes limits for the emissi ons of nitrogen oxides, sulfur

oxides, carbon monoxide and par ticulate matter from existing

power plants and cogeneration plants

Rule 323: Fuel Burning

Equipment from

Industrial/Commercial/

Institutional (ICI) Sources Establishes limits for the emissi ons of nitrogen oxides, sulfur

oxides, carbon monoxide and pa rticulate matter from ICI

sources

2 Updates to the AgBMP program in Decem ber, 2011, clarified BMPs for crop an d added BMPs for animal operations.

Effective 12/29/2011, R18-2-611 was renumbered to R18-2-610.01 Agricultural PM10 Gen eral Permit for Crop

Operations and R18-2-611.01 Animal Operations PM10 General Permit was added. Definitions for Crop Operations were

revised at R18-2-610, and new definitions for Animal Operations were added at R18-2-611.



### -19-

### Rule/Ordinance Number Description & Title

Rule 324: Stationary

Internal Combustion (IC)

Engines Establishes limits for the emissions of carbon monoxide,

nitrogen oxides, sulfur oxides , volatile organic compounds, and

particulate matter from stationary internal combustion engines,

including stationary IC e ngines used in cogeneration

Rule 325: Brick and

Structural Clay Products

(BSCP) Manufacturing Establishes limits for particulate matter emissions from the use

of tunnel kilns for curing in the brick and structural clay product

(BSCP) manufacturing processes

Ordinance P-25: Leaf

Blower Restriction Establishes restrictions for leaf blowers in incorporated and

unincorporated sections of Area A in Maricopa County

Ordinance P-26:

Residential Woodburning

Restriction Establishes restrictions for residential woodburning

Ordinance P-27: Vehicle

Parking and Use on

Unstabilized Vacant Lots Establishes restrictions fo r vehicle parking and use on

unstabilized vacant lots in unincor porated sections of Area A in

Maricopa County

Ordinance P-28: OffRoad Vehicle Use in

Unincorporated Areas of

Maricopa County Establishes restrictions fo r operating vehicles on unpaved

property in unincorporated areas of Maricopa County

Arizona Administrative

Code R18-2-611 & 610:

Agricultural PM10 General

permit Establishes a requirement for co mmercial farmers to implement

best management practices and maintain a record demonstrating

compliance

In addition to the rules and regul ations listed in Table 4-1, other PM10 reducing control measures (e.g.,

paving of unpaved roads, PM10 certified street sweep ers, controlling unpaved parking lots, etc.) have

been committed to, and implement ed by, local jurisdictions throughout the PM10 nonattainment area, and

incorporated into the Arizona SIP through PM10 pl ans such as the Revised MAG 1999 Serious Area

Particulate Plan for PM10 for the Maricopa County Nonattainment Area. The Pinal County Air Quality

Control District (PCAQCD) also implements regulat ory control measures on emissions from existing and

new non-point sources within Pinal County (see Tabl e 4-2). Additionally, the PCAQCD implements

specific nonattainment rules for that part of the P hoenix PM10 nonattainment ar ea that resides in Pinal

County (see Table 4-3).

Table 4-2. Pinal County Rules Regulating Existi ng and New Non-point Sources in Pinal County

Article Number & Title Description

Chapter 4, Article 2: Fugitive

Dust Provides a mechanism to reasona bly regulate operations which

periodically may cause fugitive dust emissions into the

atmosphere

Chapter 4, Article 3:

Construction Sites – Fugitive Dust Improves the control of excessive fugitive dust emissions that

have been traditionally associated with construction, earthwork,

and land development, and thereby minimize nuisance impacts

Table 4-3. Pinal County Rules Regulating Fugitive Dust in Pinal County Portion of Maricopa

County PM10 Nonattainment Area

-20-

### Article Number & Title Description

Chapter 4, Article 4:

Nonattainment Area Rules;

Dustproofing for Commercial

Parking, Drives and Yards Establishes rules to avoid viol ations of the prevailing PM10

standard and addi tionally minimize nuisance impacts by

improving control of excessive fugitive dust emissions from

unpaved parking lots

Chapter 4, Article 5:

Nonattainment Area Rules;

Stabilization for Residential

Parking and Drives Establishes rules for stabilizing residential properties

Chapter 4, Article 6: Restrictions

on Vehicle Parking and Use on

Vacant Lots Establishes rules for unpaved or unstabilized vacant lots (valid

in Pinal County portion of Area A)

Chapter 4, Article 7:

Construction Sites in

Nonattainment Areas – Fugitive

Dust Establishes rules to avoid viol ations of the prevailing PM10

standard and addi tionally minimize nuisance impacts by

improving control of excessive fugitive dust emissions from

activities associated with construction, earthwork, or land

development

Chapter 4, Article 8:

Nonattainment Area Rules,

Requirement for Stabilization of

Disturbed Areas at Vacant Lots Establishes rules for stabilizing disturbed areas at vacant lots

PM10 Rule Effectiveness

MCAQD analyzed the effectivenes s of its fugitive dust rules (Rul es 310, 310.01 and 316) in terms of

permit compliance rates. This ru le effectiveness (RE) study was de signed to assess how many sources

regulated by MCAQD during the subj ect time period received no PM10 emi ssions-related violations. As

a basis for comparison, the percentage of permitted s ources in compliance during calendar year 2007 was

76% for sources subject to Rule 310, 85% for Rule 310.01 sources, and 40% for Rule 316 sources. In

early 2008, Rules 310, 310.01, and 316 were strengthene d, and new ordinances (covering additional

source categories such as leaf blowers, vacant lots, and off-road vehicles) were adopted. These

enhancements resulted from MCAQD department’s obligations under such agreements as the 2005

Revised PM10 State Implementation Plan for the Sa lt River Area and the Maricopa Association of

Governments (MAG) 2007 Five Percent Plan for PM10 for the Maricopa County Nonattainment Area to

reduce PM10 emissions throughout the county. Thr ee major areas that contributed to increased

compliance were an increase in departmental staffing (especially inspectors), a robust training program,

and regulatory changes that broa dened and strengthened control measures under Rules 310, 310.01, and

316.

Source compliance rates were re-assessed for FY 2009 (July 2008–June 2009), a period that allowed time

for the new and revised regulations to take effect. The results showed significant increases in compliance

compared with the earlier period : to 90% (from 76%) for Rule 310 sources, to 95% compliance (from

85%) for Rule 310.01 sources, and to 65% (from 40 %) for Rule 316 sources. These improvements

continued into calendar year 2010 with compliance rates of 94% fo r Rule 310 sources, 96% for Rule

310.01, and 73% for Rule 316 sources. The timeline pr ovided in Figure 4-1 illustrates the improvements

in RE over the last several years, and also points out signifi cant revisions to previ ous rules, as well as

newly adopted rules and ordinances.

-21-0 1 / 27

/ 2 01

0

Rules 3 1 0 &

3 10.

0 1

R ev i s ed 0 1 / 1 2/

2 011

O rdinances

P ‐ 27

&

P

‐ 28

Revised 06/01/2005

06/08/20 0 5

Rule 3 1 6 Rev

is ed

04/

0 7/2004

R u le

3 10

Revised

0 2 /1

7 / 2 005

Rul

e 31

0 .01

Revised

0 3/26/200 8

R u les

31

0 &

3 10

.0 1 Revised

M arc h 20 08 S e p tem b er 200 6

0 2/

2 0/20 08

O rdina n ces

P ‐ 25,

P

‐ 27

&

P ‐ 2 8

Adopted

0 3/12/20 0 8

R u le

3 16

Revised



### Figure 4-1. Timeline of Maricopa County Fugitive Dust Rules and Ordinances.

Compliance and Enforcement Activities

MCAQD is proactively prepared to respond to high wind events and to protect human health and wellbeing. MCAQD’s approach consists of two primary components: routine proactive inspections and

surveillance inspections, conducted both during and after signifi cant events. MCAQD proactively

inspects dust control-permitted sites, and increases the frequency for larger sites of 10 acres or more.

Rule 316 sources are also proactively inspected mu ltiple times every year. Maricopa County also

responds to the majority of complaints within 24 hours.

Maricopa County monitors the ADEQ Five-Day Dust Control Forecast to iden tify the potential for

elevated PM10 pollution levels due to high winds or stagnant c onditions. When a High Pollution

Advisory (HPA) is issued for Maricopa County, MC AQD conducts additional surveillance before, during,

and after the forecast event(s). MCAQD also conduc ts event surveillance a nd post-event activities on

exceedance days that had not been forecast (i.e., thos e instances in which an HPA had not been issued).

Pre-event surveillance consists of surveying high-risk areas for any dust-generating activ ities; educating

sources of the impending HPA event; a nd issuing violations for failure to comply with local, state, or

federal regulations. During the event, MCAQD inspector s survey high-risk areas to confirm that control

measures are in place, document any violations, and contact other regulatory agen cies if necessary. Postevent activities include continued surv eys of high-risk areas, re-inspect ion of sources that had received

violations within two business days, and an internal MCAQD debriefing of event activities.

Recently, a total of 12 MCAQD air monitoring sites have been updated with new equipment that allows

the monitoring sites to report automatically monitored re adings at five-minute intervals, where previously

only hourly data were available. The real-time monitoring data progr amming includes threshold triggers

that cause the system to send al erts to MCAQD staff that the PM concentrations are elevated. The system

allows MC AQD responders to review concentrations at the monitor and to cons ult the National Weather

Service website to check for weathe r event activity. This capability allows the responder to identify

regional events and monitor specifi c issues. If necessary, the MC AQD responders can inform nearby

stakeholders and local governments of the elevated PM10 concentrations.

-22-

### For July 18, 2011, a Maricopa County Dust Control Foreca st was issued indicating a moderate risk level

for unhealthy PM 10 

### . The Dust Control Forecast also indicated a potential for strong and gusty winds, and

a potential for dense blowing and transported dus t generated by outflow from thunderstorms.

An evaluation of inspection reports and comp liance records indicate no evidence of unusual

anthropogenic-based PM 10 

### emissions. During the time period of July 15 through July 21, 2011, MCAQD

inspectors conducted a total of 165 inspections of perm itted facilities, of which 147 were at fugitive dust

sources. Additionally, MCAQD conducted 91 inspecti ons on vacant lots and unpaved parking lots.

During this 7-day period, a total of 16 vi olations were issued county-wide for PM 10 

### and non-PM 10 

### -related

violations. Two violations were issued for PM 10 

### emissions within a 4-mile radius of an exceeding

monitor; West Phoenix and Central Phoenix.

On July 15, 2011, a violation was issued to an owner of a vacant lot for failure to stabilize surface areas

that had been disturbed by horse-rid ing activity. The vacant lot is loca ted 3.2 miles southwest of the West

Phoenix monitor, and the total disturbed surface area was 0.11 acres. No horse-riding activity was

observed during the inspection. The violation was the result of a co mplaint MCAQD received on July 15.

The owner was issued a 60-day letter informing them of the stability issue. The owner stabilized the area,

installed “No Trespassing” signs, and provided the City of Phoeni x with the authority to arrest any

trespassers on the property.

Additionally on July 15, 2011, a violation was issued to an owner of a re sidence for parking vehicles on a

dirt surface that did not meet the control measur es requirements of Rule 310.01 Section 302.6(b). The

residence is located 2.4 miles north of the Central Phoenix monitor. The violation was the result of a

complaint MCAQD received on July 14, 2011. Though the unpaved parking area did not meet the control

measure requirements of Rule 310.01, Section 302.6(b), the inspector did not obs erve unstabilized areas

during the inspection. The owner of the residence was issued a 60-day le tter informing him of the control

measure requirements. No compliance issues were observed on subsequent inspections.

MCAQD was prepared for any complaints received due to the high wind event. During the 7 day period

from July 15 through July 21, 2011, MCAQD received 36 complaints, of which 30 were windblown dustrelated. Each complaint was assigned to and inve stigated by a MCAQD inspect or. A review of all

records during this period reveals th at MCAQD inspectors only observed two PM 10 

### violations of local,

state, or federal regulations within a 4- mile radius of the exceeding monitors.

In addition to MCAQD’s efforts in pre-event surveillance and proact ive inspections, ADEQ’s

Agricultural Best Management Practice Program (Ag BMP) inspector monitors the ADEQ Five-Day Dust

Control Forecast and the MCAQD air monitoring sites that include real-time data. The ADEQ Ag BMP

inspector uses specific knowledge of seasonal activities and associa tions with the local growers and

dairymen to communicate the importance of limiting dust-generating activities, especially during highwind events. Additional outreach is conducted with facility representati ves prior to for ecasted high-wind

alert days. Should the PM10 readings at a MCAQD ai r monitoring site show notable increases, the

ADEQ Ag BMP inspector is dispatched to contact the owners and operators of ag riculture fields in the

area to discern if their activities ar e causing negative impacts. The Ag BMP inspector is prepared to

respond to most agriculture complaints within 24 hours.

Based on a review of the inspection reports and site visit documentation, there is no evidence to suggest

that agricultural activit ies produced unusual PM10 emissions. From July 19 through July 22, 2011, the

ADEQ Ag BMP inspector received three complaints and performed site visi ts at one agricultural

-23-

### operation. The agriculture fields vi sited had established crops of cor n, which would not have contributed

to PM10 emissions.

Conclusions

The thunderstorm outflow event of July 18, 2011, pr oduced strong gusts and turbulent wakes that

transported dust and PM10 into the Phoenix PM10 nona ttainment area. The sour ce region of the outflows

that caused the exceedances was largely located in areas outside the Phoenix PM10 nonattainment area,

primarily the deserts of Pinal, Pima, and southern Maricopa County. The Phoenix area is designated as a

serious nonattainment area for PM10 and is required to have BACM for all sign ificant sources of PM10.

BACM-approved control measures on significant anthropogenic sources were in place and enforced

during the events, and pro-active tr acking and response to the events by regulatory agencies and local

governments confirmed the uncontrollabl e nature of the dust emissions; th erefore, these pr e-existing/prior

approved required controls are adequate for meeting th e requirements of an ex ceptional event and should

be considered “reasonable” for these purposes.

Despite the deployment of comprehensive control m easures and sophisticated response programs and a

few localized, low-impact violati ons of the dust control rules, hi gh wind conditions associated with

thunderstorms and thunderstorm outflows brought high concentrations of PM10 emissions into, and also

overwhelmed controls within, the Phoenix PM10 nonattainment area. Strong thunderstorm outflows with

sustained winds typically ranging from 20-30 mph, and even greater ne arest the source regions, were

enough to overwhelm all available efforts to limit PM10 concentrations from the events. The fact that

these were natural events involvi ng strong thunderstorm outflow winds that transported PM10 emissions

into Maricopa County, with a majority of the PM10 emissions recorded by Maricopa County area

monitors coming from sources outside of the Phoenix PM10 nonattainment area, provides strong evidence

that the events and exceedances of July 18, 2011, r ecorded within the Phoenix PM10 nonattainment area,

were not reasonably controll able or preventable.

-24-

## V. CLEAR CAUSAL RELATIONSHIP

Introduction

A demonstration of the clear causa l connection between uncontrollable natural events or uncontrollable

emissions associated with thunderstorm outflows and PM10 exceedances on July 18, 2011, is presented in

the following time series graphs, infrared satellit e imagery, and National Weather Service (NWS) data

tables for selected, representative airports. These various pieces of information contain data on sustained

wind speed, wind speed gusts, PM10 c oncentrations, visibility, weathe r observations, and thunderstorm

development areas and provide the causal connection between the uncont rollable emissions associated

with thunderstorm outflows and elevated PM10 concentrations. For reference, Appendix D provides

additional NWS text products issued preceding and on July 18 containing forecasts and warnings of

blowing dust due to thun derstorms outflows. A summary of the event day is provided below.

Event – July 18, 2011

On July 18, 2011, the Phoenix region experienced typical summertime weather conditions with a

maximum temperature of 111°F, relative humidity of 10-30%, winds at 5-12 miles per hour (mph) from

various directions, and visibility at 10 miles all day, as reported at the Phoenix Sky Harbor Airport.

Despite a spike in PM10 concentrations at most of the PM10 monitoring sites in the region late on July 17

due to windblown dust caused by moderate thunderst orm outflow winds, PM10 concentrations on July 18

were generally very low all day (20-50 μg/m 3 

### range). Between 3 p.m. Mountain Standard Time (MST)

and 5 p.m. MST on July 18, severe thunderstorms devel oped over portions of Arizona to the southeast of

the Phoenix region (as shown in Fi gure 5-1) and by 4 p.m., outflows from the thunderstorms entrained

dust from desert areas of Pinal County and generate d a “haboob” that progre ssed northwestward into

Maricopa County, transporting larg e amounts of PM10. As shown in Figure 5-2, the “haboob” had the

following impacts in the Phoenix area: southeasterly winds increased to 21-25 mph, with gusts up to 37

mph; visibility dropped from 10 miles to 1 mile ; weather conditions were reported as “haze” and

“blowing dust”; and hourly PM10 concentr ations increased to nearly 3000 μg/m 3 

### at the South Phoenix

monitoring site and exceeded 1500 μg/m 3 

### at six sites. Once the winds su bsided, visibility remained below

10 miles and PM10 concentrations remained high fo r several hours, resulti ng in 24-hour average

concentrations above 200 μg/m 3 

### at five monitoring sites on July 18. In total, eight monitoring sites in the

region exceeded the PM10 NAAQS and, as was mentioned in the Historical Fluctu ation section, most of

those eight PM10 monitoring sites saw one of thei r 10 highest 24-hour averag e PM10 concentrations

measured in the past five years. Without the ex istence of the emissions generated by the thunderstorm

outflows, there would not have been any exceedances of the 24-hour PM10 standard in the Phoenix PM10

nonattainment area.

-25-

### 11:00 a.m

. 2:00 p.m. 4:00 p.m. 6:00 p.m.

1800z Jul 18 2100z Jul 18 2300z Jul 18 0100z Jul 19

8:00 p.m. 10:00 p.m. 12:00 a.m. 2:00 a.m.

0300z Jul 19 0500z Jul 19 0700z Jul 19 0900z Jul 19

Figure 5-1. Satellite imagery showing strong storms developing and dissipating over Pinal County and

areas to the southeast of Phoenix. These storms are believed to have b een responsible for the

thunderstorm outflow boundary that caused PM10 exceed ances in Maricopa and Pinal counties on July

18.

Figure 5-2 depicts the dust event th at occurred in Maricopa County im pacting the Phoenix area on July

18. Hourly averaged PM10 concentrations at m onitors throughout Maricopa County are shown along

with visibility readings (blue di amonds) and wind speeds reported at the Phoenix Sky Harbor Airport.

Measurements at Sky Harbor were used due to its central location amongst most of the monitors that

experienced exceedances on July 18. As can be seen in the graph, visibility was reduced down to 1 mile

at the Sky Harbor Airport during th e windblown dust event, and this visi bility reduction coincided with

rapidly increasing PM10 concentrations and sustained wind speeds up to 25 mph in the Phoenix area.

The NWS data tables after Figure 5-3 also show re ports of haze and blowing dust during the 6 p.m. ho

when PM10 concentrations were the highest. ur,

A review of the 5-minute wind and PM 10 data at several of the Maric opa County monitoring sites showed

that within 15 minutes, rapid wind speed increases a nd significant wind direction changes associated with

the arrival of the haboob produced very rapid spikes in PM10 concentrations. For example, the

Greenwood site, near the intersectio n of highways I10 and I17, had 5-mi nute average winds at 8 mph out

of the east-southeast and a PM10 concentration of 68 μg/m 3 

### at 5:40 p.m. By 5:55 p.m., the 5-minute wind

speed average had increased to over 18 mph out of the south and PM10 concentrations reached 4704

μg/m 3 

### . Similarly, as the haboob raced to the northwest, the Dysart monitoring site had 5-minute average

winds at 2 mph out of the southwest and a PM10 concentration of 20 μg/m 3 

### at 6:00 p.m.; however, by

6:15 p.m., the 5-minute average winds had exceeded 26 mph out of the southeast and PM10

concentrations reached 2964 μg/m 3 

### . It was clearly evident that a thunderstorm outflow boundary had

passed through the Phoenix region a nd the direction of flow caused the greatest increases in PM10

concentrations in the central and western portions of the Phoenix PM10 nonattainment area.

-26-

### As shown in Figure 5-3, several m onitoring sites in the upwind, dust source region of Pinal County

measured 24-hour average PM10 exceedances, with the peak site—Cowtow n—having a 24-hour average

of 1,638 μg/m 3 

### and an extremely high maximum 1-hour average during the 5 p.m. hour of 24,976 μg/m 3



### . Two other monitoring sites also measured concentrations of nearly 10,000 μg/m 3 

### . These spikes preceded

the PM10 concentration spikes at the monitoring s ites in Maricopa by one to two hours, which is

consistent with wind speeds and directions observed at the Phoenix Sky Harbor Airport in Maricopa

County and the Casa Grande Airport in Pinal Count y for the propagation of th e haboob across the region.

Only monitoring sites in Maricopa and Pinal counties exceeded the NAAQS due to thunderstorm

outflows on this day, but the broad range of site s and the extreme hourly- and daily-averaged PM10

concentrations reflect the magnitude of the “haboob.” Additionally, the NWS airport meteorological data

tables for the Phoenix Sky Harbor and Casa Grande airp orts show that the stronge st winds associated with

the haboob were out of the southeast. These winds, co mbined with the high PM10 concentrations in Pinal

County, indicate that PM10 was alr eady entrained in the atmosphere outside of the Phoenix PM10

nonattainment area and then transporte d into the region by the strong winds.

A visualization of this dust event wa s created using Phoenix visibility camera images that can be viewed

as an animation here:

Looking south toward Phoenix, with South Mountain in the distance:

www.phoenixvis.net/videos/ m peg4/SOMT_07182011.mp4

The video clearly shows the wall of dust blowing across the Phoenix re gion in the late afternoon/early

evening of July 18, 2011. The snapshot on the cover of this report was taken fr om the 5:50 p.m. mark of

the video and coincides exactly with the PM10 concentration spikes seen in the 5-minute data from the

PM10 monitoring sites in the central Phoenix area. Videos showing other views across the Valley on this

date are also available (see Visibility Cameras section).

-27-

### Figure 5-2. Phoenix nonattainm ent area PM10 monitor read ings and Sky Harbor wind speed and

visibility for July 18, 2011.

-28-

### Figure 5-3. Pinal County PM10 m onitor readin gs and Casa Grande wind speed and visibility for July 18,

2011.

-29--30-U.S. Department of CommerceNational Oceanic & Atmospheric AdministrationQUALITY CONTROLLED LOCALCLIMATOLOGICAL DATA (final)HOURLY OBSERVATIONS TABLEPHOENIX SKY HARBOR INTL AIRPORT(23183) PHOENIX, AZ (07/2011)National Climatic Data CenterFederal Building151 Patton AvenueAsheville, North Carolina 28801Elevation: 1107 ft. above sea levelLatitude: 33.427Longitude: -112.003Data Version: VER3DryBulbTempWetBulbTempDewPointTempDateTime(LST)StationTypeSkyConditionsVisibility(SM)WeatherType(F)(C)(F)(C)(F)(C)RelHumd%WindSpeed(MPH)WindDirWindGusts(MPH)StationPressure(in. hg)PressTendNet3-hrChg(mb)SeaLevelPressure(in. hg)ReportTypePrecip.Total(in)Altimeter(in. hg)123456789101112131415161718192021222318181818181818181818181818181818181818181818181818181818181818005101510251035104510551065107510851095110511151125113511451155116511739175118161830183118511901192219512014205121512251235111111111111111111111111111111111111111111111111111111111111111SCT150 BKN200SCT150 BKN200SCT150 BKN200SCT150 BKN200SCT150 BKN200SCT150 SCT200FEW180 BKN210FEW180 SCT210FEW180 SCT210FEW180 SCT210FEW095 SCT180 SCT210FEW100 SCT210 SCT250FEW110 SCT210 SCT250FEW120 SCT210 SCT250FEW120 SCT210 SCT250FEW120 SCT210 SCT250FEW120 SCT210 BKN250FEW006 SCT120 SCT190SCT009 SCT029 SCT120BKN022 BKN120 BKN180BKN022 BKN120 BKN250BKN022 BKN120 BKN250BKN020 BKN120 OVC250BKN030 BKN120 BKN250BKN030 BKN120 BKN250SCT030 BKN120 BKN160SCT045 BKN120 BKN160SCT090 BKN140 BKN230SCT090 BKN140 BKN230SCT090 BKN140 BKN230SCT090 BKN140 BKN23010.0010.0010.0010.0010.0010.0010.0010.0010.0010.0010.0010.0010.0010.0010.0010.0010.0010.006.005.002.001.001.001.002.002.003.003.0010.0010.0010.00HZ BLDUHZ BLDUHZ BLDUHZ BLDUHZ BLDUHZ95939392919092949599100104106107108111108108103100999997979595959595949335.033.933.933.332.832.233.334.435.037.237.840.041.141.742.243.942.242.039.438.037.037.036.136.035.035.035.035.035.034.433.97071717070707171717272727272717273727272717171717070707170707121.321.521.821.321.221.021.621.621.822.122.022.422.222.321.822.122.522.022.022.021.921.921.621.621.321.321.321.521.321.121.55759605959596059595857565454515054525557575757575757575857575913.915.015.615.015.015.015.615.015.014.413.913.312.212.210.610.012.211.012.814.014.014.013.914.014.013.914.014.413.913.915.0283233333435343130262420181715131716202425252626282828292829328106776883868100510132125231616131315138111198150140120160160160140150150100VR16010000017019012013014019018019021017016014015011011011013016172030373028281828.6528.6528.6528.6528.6628.6628.6828.6928.6928.6928.6828.6628.6428.6128.5928.5828.5728.5728.5828.6228.6428.6528.6628.6628.6628.6528.6428.6528.6628.6828.690318860300400101200302401502701029.7529.7529.7529.7529.7529.7729.7829.7929.7929.7929.7829.7729.7429.7129.6929.6829.66M29.68MMM29.76MM29.75M29.7629.7729.7829.79AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAASPAASPSPSPAASPSPAASPAAAAAAAA29.8229.8229.8229.8229.8329.8429.8529.8629.8629.8629.8529.8429.8129.7829.7629.7529.7429.7429.7529.7929.8129.8229.8329.8329.8329.8229.8129.8229.8429.8529.86Dynamically generated Wed Oct 31 17:28:33 EDT 2012 viahttp://cdo.ncdc.noaa.gov/qclcd/QCLCD-31-U.S. Department of CommerceNational Oceanic & Atmospheric AdministrationQUALITY CONTROLLED LOCALCLIMATOLOGICAL DATA (final)HOURLY OBSERVATIONS TABLECASA GRANDE MUNICIPAL ARPT (03914)CASA GRANDE, AZ (07/2011)National Climatic Data CenterFederal Building151 Patton AvenueAsheville, North Carolina 28801Elevation: 1462 ft. above sea levelLatitude: 32.95Longitude: -111.766Data Version: VER2DryBulbTempWetBulbTempDewPointTempDateTime(LST)StationTypeSkyConditionsVisibility(SM)WeatherType(F)(C)(F)(C)(F)(C)RelHumd%WindSpeed(MPH)WindDirWindGusts(MPH)StationPressure(in. hg)PressTendNet3-hrChg(mb)SeaLevelPressure(in. hg)ReportTypePrecip.Total(in)Altimeter(in. hg)1234567891011121314151617181920212223181818181818181818181818181818181818181818181818181818181818181818181818001500350055011501350155021502350255031503350355041504350455051505350555061506350655071507350755081508350855091509350955101510351055111511351155000000000000000000000000000000000000CLRCLRCLRCLRCLRCLRCLRCLRCLRCLRCLRCLRCLRCLRCLRCLRCLRCLRCLRCLRCLRCLRCLRCLRCLRCLRCLRCLRCLRCLRCLRCLRCLRCLRCLRCLR10.0010.0010.0010.0010.0010.0010.0010.0010.0010.0010.0010.0010.0010.0010.0010.0010.0010.0010.0010.0010.0010.0010.0010.0010.0010.0010.0010.0010.0010.0010.0010.0010.0010.0010.0010.0091919191909090909088888888888686868488889090909091919395959799979910010210033.033.033.033.032.032.032.032.032.031.031.031.031.031.030.030.030.029.031.031.032.032.032.032.033.033.034.035.035.036.037.036.037.038.039.038.069696869697070696968696969686969696769697070707171717171717171727172727220.620.620.020.620.421.021.020.420.420.120.620.620.620.120.320.320.319.420.620.621.021.021.021.521.721.721.421.821.821.521.822.121.822.022.322.057575557575959575757595959575959595759595959596161615959595757595757575714.014.013.014.014.015.015.014.014.014.015.015.015.014.015.015.015.014.015.015.015.015.015.016.016.016.015.015.015.014.014.015.014.014.014.014.0323230323335353333353838383540404040383835353538373732303026252825242324111413899506000000065779810666711857307031101001101301301201200001100000000000000000000000500700500800901001101001101001201201001301700700001000001502228.3428.3428.3228.3228.3228.3228.3128.3028.3128.3228.3228.3228.3228.3228.3228.3328.3228.3328.3428.3428.3428.3528.3528.3528.3528.3528.3528.3528.3528.3528.3528.3528.3428.3428.3428.33247003000003MMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA29.8929.8929.8729.8729.8729.8729.8629.8529.8629.8729.8729.8729.8729.8729.8729.8829.8729.8829.8929.8929.8929.9029.9029.9029.9029.9029.9029.9029.9029.9029.9029.9029.8929.8929.8929.88-32-DryBulbTempWetBulbTempDewPointTempDateTime(LST)StationTypeSkyConditionsVisibility(SM)WeatherType(F) (C) (F) (C) (F) (C)RelHumd%WindSpeed(MPH)WindDirWindGusts(MPH)StationPressure(in. hg)PressTendNet3-hrChg(mb)SeaLevelPressure(in. hg)ReportTypePrecip.Total(in)Altimeter(in. hg)12345678910 11 12 13141516171819 20212223181818181818181818181818181818181818181818181818181818181818181818181818121512351255131513351355141514351455151515351555161516351655171517351755181518351855191519351955201520352055211521352155221522352255231523352355000000000000000000000000000000000000CLRCLRCLRCLRCLRCLRCLRCLRCLRCLRBKN011FEW011CLRCLRBKN006 BKN011CLRCLRCLRCLRCLRCLRCLRCLRCLRCLRCLRCLRCLRCLRCLRCLRCLRCLRCLRCLRCLR10.0010.0010.0010.0010.0010.0010.0010.0010.0010.001.508.0010.004.001.009.005.0010.0010.003.002.505.007.0010.0010.0010.0010.0010.0010.0010.0010.0010.0010.0010.0010.0010.00VCTSVCTS1021021021021041061041061081081061021061049597939195919193919191919191909090888886868439.039.039.039.040.041.040.041.042.042.041.039.041.040.035.036.034.033.035.033.033.034.033.033.033.033.033.033.032.032.032.031.031.030.030.029.072727172737272727373737273737271707069706969706969696969696969697070706922.322.321.822.322.622.422.122.422.722.722.822.322.822.622.321.520.921.120.721.120.620.421.120.620.620.620.620.620.420.420.420.621.220.920.920.557575557575555555555575757576157575955595755595757575757575757596161616114.014.013.014.014.013.013.013.013.013.014.014.014.014.016.014.014.015.013.015.014.013.015.014.014.014.014.014.014.014.014.015.016.016.016.016.02323212321192019171720232021322630342634322834323232323233333338404343465963050811630s21202629282928181816139100855100675650110060110100000070000190140290070060080110120120150150150170160160210170000150150090100000110130130120140000183433263438373729252128.3228.3228.3128.2928.2828.2728.2728.2728.2728.2528.2528.2528.2528.2728.2828.2728.2828.2828.2828.2828.2828.2828.3028.3028.3228.3228.3228.3328.3328.3428.3428.3428.3528.3528.3628.36722024003007MMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA29.8729.8729.8629.8429.8329.8229.8229.8129.8129.8029.8029.8029.8029.8229.8329.8129.8329.8329.8329.8329.8329.8329.8529.8529.8729.8729.8729.8829.8829.8929.8929.8929.9029.9029.9129.91Dynamically generated Wed Oct 31 15:26:23 EDT 2012 viahttp://cdo.ncdc.noaa.gov/qclcd/QCLCD

### Visibility Cameras

Visibility camera images were compiled into tim e lapse photography videos in order to visually

show the dust impacts on portions of Maricopa County on July 18. The animations are available

online for each event and for each of the visibi lity camera sites in Maricopa County. These

views can be accessed using the camera site co des SOMT (South Mountain), CAME (Camelback

Mountains), SUPM (Superstiti on Mountains), ESMO (Estrella Mountains), and WHTM (White

Tank Mountains). It should be noted that thes e time lapse photography videos may require the

installation of a mp4 viewer.

The video files can be accessed as follows:

http://www.phoenixvis.net/videos/mpeg4/xxxx_mmddyyyy.mp4

xxxx = 4-character site code (ie. SOMT)

mm = 2-character month (ie. 07)

dd = 2-character day (ie. 18)

yyyy = 4-character year (ie. 2011)

Conclusion

The information presented within this section has adequately demonstrated a clear causal

relationship between the emissions generate d by uncontrollable natu ral events and the

exceedances measured at the monitors. The sa tellite images, time series graphs, and

meteorological data tables provided in this se ction show the temporal progression of the dust

events from the development of th e thunderstorms, to the increase in wind speeds, and to the rise

in PM10 concentrations. The combination of the PM10 and wind data from Maricopa and Pinal

counties shows the transport of pa rticulate matter from the south through Pinal County and into

the Phoenix PM10 nonattainment area. This inform ation supports the conclu sion that the events

were primarily drawing from emission sources outside of Maricopa County and were being

transported into the Phoenix area.

-33-

## VI. “BUT FOR” ANALYSIS

Section 50.14(c)(3)(iv)(D) in 40 CFR part 50 re quires that an exceptional event demonstration

must satisfy that “[t]here would have been no exceedance or violation but for the event.” The

prior sections of this submittal have provided detailed information that the exceedances on July

18, 2011, were not reasonably contro llable or preventable and there is a clear causal relationship

between transported PM10 from thunderstorm outflow s originating in the desert areas outside of

the Phoenix PM10 nonattainment area and the m easured exceedances within the nonattainment

area. The weight of evidence in these sections demonstrates that but for the existence of

emissions generated by these thunderstorm outfl ows and associated transported PM10, there

would have been no exceedances of the 24-hour PM10 standard.

As detailed in Section IV, all reasonable control measures were in place and actively enforced

before, during, and after the exceedances of Ju ly 18, 2011. Inspection and compliance data of

local fugitive dust sources duri ng this time period revealed that PM10 from anthropogenic

activities was well controlled and constant. Loca l regulatory agencies, industry, and the general

public were alerted to the possi bility of dust storms due to thunderstorm activ ity through daily

forecasts and media reports. Heightened, real -time surveillance of PM10 monitoring stations

during the events established a clear link between rapidly risi ng PM10 concentrations and the

arrival of the thunderstorm outfl ows. On-the-ground observations recorded during the events

consistently identify transported or re-entrained PM10 as the cause of the elevated concentrations

near the exceeding monitors.

As shown in Section V, detailed, time series data establish a clear causal relationship between

the arrival of emissions generated by thundersto rm outflows and elevated PM10 concentrations

at the monitors. Multiple, independent meas urements of wind speed, wind direction, and

visibility all point to the pr esence of thunderstorm outflows as the delivery vehicle for

transported PM10 into the nonattainment area. Any local PM10 emissions generated during the

arrival of the thunderstorm outfl ows are linked to the turbulent and gusty outflow front of the

storm and pale in comparison to the amount of transported PM10 originating outside the

nonattainment area. The source regions for the thunderstorm outflows and transported PM10 are

clearly identified as the de sert areas outside of the P hoenix PM10 nonattainment area.

The body of evidence presented in this submitta l provides no alternativ e that could tie the

exceedances of July 18, 2011, to any other causal source but transported and re-entrained PM10

generated from thunderstorm outflows, confirming that there would have been no exceedances

but for the presence of thes e uncontrollable natural events.

-34-

## VII. CONCLUSIONS

The exceedances that occurred on July 18, 2011, satisfy the following criteria of 40 CFR 50.1(j)

and meet the definition of an exceptional event:

 The event affects air quality;

 The event is not reasonably cont rollable or preventable; and

 The event is unlikely to reoccur at a partic ular location or [is] a natural event.

Affects Air Quality

As stated in the preamble to the Exceptional Even ts Rule, the event in question is considered to

have affected air quality if it can be shown that there is a cl ear causal relationship between the

monitored exceedance and the event, and that the event is associated with a measured

concentration in excess of normal historical fl uctuations. Given the information presented in

Sections 2, 3, 4, and 5, we can reasonably conclude that the event in question affected air quality.

Not Reasonably Controllable or Preventable

Section 50.1(j) of Title 40 CFR Part 50 require s that an event must be “not reasonably

controllable or preventable” in orde r to be defined as an exceptiona l event. This requirement is

met by demonstrating that, despite reasonable cont rol measures in place w ithin Maricopa County

and the Phoenix PM10 nonattainment area, high wind conditions overwhelmed all reasonably

available controls. Despite the deployment of comprehensive cont rol measures and sophisticated

response programs, high wind conditions associ ated with thunderstorms and thunderstorm

outflows brought high concentrations of PM10 emi ssions into, and also overwhelmed controls

within, the Phoenix PM10 nonattainment area. The event discussed in this document that caused

the exceedances in this request (see Sections II and V) were caused by thunderstorm-driven

outflow winds that transported dust into Maricopa County from areas largely outside of the

Phoenix PM10 nonattainment area. The fact that these were natural events involving strong

thunderstorm outflow winds that transported PM10 emissions into Maricopa County, with a

majority of the PM10 emissions recorded by Maricopa County area monitors coming from

sources outside of the Phoenix PM10 nonattainment area, provides strong evidence that the event

and exceedances of July 18, 2011 recorded within the nonattainment area were not reasonably

controllable or preventable.

Natural Event

As discussed above, the events shown to cause these exceedances were emissions of PM10

driven by high winds caused by thunderstorm ac tivity and related outflow boundaries on July 18,

2011. The events therefore qualify as natural events.

-35-

### -36- Summary

In summary, the exceedances of the federal 24-hour PM10 standard on July 18, 2011, would not

have occurred but for the monsoonal thunderstorm-driven high winds and windblown dust

transport from areas largely outside the Phoe nix PM10 nonattainment area, based on the weight

of evidence summarized below.

 Graphs of PM10 at various Phoenix area monitors in Section V and the tables containing

meteorological data for representative NWS air port sites show that the timing of elevated

PM10 events was consistent with decreased visi bility and high winds at the NWS sites.

 Visibility camera imagery discussed in Sec tion V indicates that la rge quantities of PM10

were transported into the Phoe nix Metro area during the July 18 th 

### event. The timing of

the dust storms depicted in the visibility camera imagery is consistent with the PM10

concentration measurements, elevated winds, and reduced visibility reported during the

event.

 Historical Fluctuation analyses and graphs in Section III and Appendix A showing five

years of 24-hour average data for each of the Phoenix PM10 nonattainment area monitors

depict numerous atypically high PM10 concentrations during the third quarter of 2011,

including the day of July 18. The sudden in crease in the frequency of elevated PM10

concentrations during this time period was ex ceptional from an hist orical perspective.

 Each of the exceedances of the PM10 standard recorded on July 18 is tied to

thunderstorm activity and thunderstorm generate d outflow winds, as can be seen in data

and analyses in Section V.

 Figures and tables in Section V show that the timing of thunderstorm-generated outflow

boundary passage and increases in wind speeds at monitoring locations and National

Weather Service stations during each of the events during this period is consistent with

the timing of elevated PM10 concentrations recorded at th e monitoring locations in the

Phoenix PM10 nonattainment area.

 Wind directions, thunderstorm-generat ed outflow boundary propagation, and

concentration patterns showing elevated levels of PM10 in Pinal County prior to levels

increasing in Maricopa County, a ll depicted in Section V, help show that a vast majority

of the dust that impacted Phoenix PM10 nonattainment area monitors originated in Pinal

County and other areas located gene rally south of the Phoenix PM10 nonattainment area.

 Section IV discusses rules that are in place in the Phoenix PM10 nonattainment area as

well as inspections that were conducted in th e area to verify compliance with those rules

in order to show that the events are not reasonably controllable or preventable.

Additionally, the visibility webcam time laps e photography videos referenced in Section

II help illustrate the magnitude and scale of these events, which supports the claim that

the exceedances recorded during this peri od were not reasonably controllable or

preventable.

## APPENDIX A

5

- YEAR HISTORICAL FLUCTUATION GRAPHS FOR

THE PHOENIX PM10 NONATTAINMENT AREA MONITORING SITES050100150200250300350400450500

PM 10 Concentration (μg/m

3 )DateBuckeye 5-Year Historical Fluctuation - 24 Hour Averages050100150200250300350400450500

PM 10 Concentration (μg/m

3 )DateCentral Phoenix 5-Year Historical Fluctuation - 24 Hour Averages050100150200250300350400450500

PM 10 Concentration (μg/m

3 )DateWest Phoenix 5-Year Historical Fluctuation - 24 Hour Averages050100150200250300350400450500

PM 10 Concentration (μg/m

3 )DateGreenwood 5-Year Historical Fluctuation - 24 Hour Averages050100150200250300350400450500550

PM 10 Concentration (μg/m

3 )DateJLG Supersite 5-Year Historical Fluctuation - 24 Hour Averages050100150200250300350400450500

PM 10 Concentration (μg/m

3 )DateWest 43rd 5-Year Historical Fluctuation - 24 Hour Averages050100150200250300350400450500

PM 10 Concentration (μg/m

3 )DateSouth Phoenix 5-Year Historical Fluctuation - 24 Hour Averages050100150200250300350400450500

PM 10 Concentration (μg/m

3 )DateDurango 5-Year Historical Fluctuation - 24 Hour Averages050100150200250300350400450500

PM 10 Concentration (μg/m

3 )DateWest Chandler 5-Year Historical Fluctuation - 24 Hour Averages050100150200250300350400450500

PM 10 Concentration (μg/m

3 )DateHigley 5-Year Historical Fluctuation - 24 Hour Averages050100150200250300350400450500

PM 10 Concentration (μg/m

3 )DateGlendale 5-Year Historical Fluctuation - 24 Hour Averages050100150200250300350400450500

PM 10 Concentration (μg/m

3 )DateDysart 5-Year Historical Fluctuation - 24 Hour Averages050100150200250300350400450500

PM 10 Concentration (μg/m

3 )DateZuni Hills 5-Year Historical Fluctuation - 24 Hour Averages050100150200250300350400450500

PM 10 Concentration (μg/m

3 )DateApache Junction 5-Year Historical Fluctuation - 24 Hour Averages

## APPENDIX B

ADEQ F ORECAST PRODUCTS FOR PHOENIX

, MARICOPA COUNTY, AND PINAL COUNTY

## MARICOPA COUNTY DUST CONTROL FORECAST

ISSUED SUNDAY, JULY 17, 2011

Five-day weather outlook:

DURING ACTIVE SUMMER MONSOON EPISODES STRONG GUSTY WINDS AND DENSE BLOWING DUST ARE

POSSIBLE EVEN FROM DISTANT THUNDERSTORMS

The summer monsoon circulation pattern has resumed and for the Phoenix metro area this means a slight chance for thunderstorms

each day thru this forecast period. Gradient winds will be relatively light. Since la st week’s rainfall has reduced but not e liminated

the risk for periods of dense blowing and/ or transported dust generated by outflow boundaries, there will be a moderate risk fo r

unhealthy PM-10 levels.

RISK FACTORS

WINDS STAGNATION UNHEALTHY PM-10

RISK LEVEL

Day 1: Mon 07/18/2011 No significant winds

expected except strong

and gusty due to

outflow from

thunderstorms. + No significant

stagnation expected. = MODERATE

Day 2: Tue 07/19/2011 No significant winds

expected except strong

and gusty due to

outflow from

thunderstorms. + No significant

stagnation expected. = MODERATE

Day 3: Wed 07/20/2011 No significant winds

expected except strong

and gusty due to

outflow from

thunderstorms. + No significant

stagnation expected. = MODERATE

EXTENDED OUTLOOK

Day 4: Thu 07/21/2011 No significant winds

expected except strong

and gusty due to

outflow from

thunderstorms. + No significant

stagnation expected. = MODERATE

Day 5: Fri 07/22/2011 No significant winds

expected except strong

and gusty due to

outflow from

thunderstorms. + No significant

stagnation expected. = MODERATE

The Maricopa County Dust Control Action Forecast is issued to assist in the planning of work activities to

help reduce dust pollution. A recorded message of this forecast can be accessed at 602-771-2368 . To review

the complete air quality forecast for the Phoenix metropolitan area, as well as the health impacts and

reduction methods for different air pollutants, call 602-771-2367 for recorded forecast information or click on

ADEQ's Air Quality Forecast at http://www.azdeq.gov/environ/air/oz one/ensemble.pdf

. CKR 04/28/2011VERY UNHEALTHY (201-300)

UNHEALTHY (151-200)

UNHEALTHY FOR SENSITIVE GROUPS (101-150)

MODERATE (51-100)

GOOD (0-50)

For more information visit:

http://www.airnow.gov/index.cfm?action=aqibasics.aqi

NEW!!! CLICK HERE FOR UPDATED OZONE SEASON STATS NEW!!!



### AIR QUALITY FORECAST FO R MONDAY, JULY 18, 2011

This report is updated by 1:00 p.m. Sunday thru Friday and is valid

for areas within and bordering Maricopa County in Arizona

* O3 = Ozone CO = Carbon Monoxide PM-10 = Particles 10 microns & smaller PM-2.5 = Particles smaller than 2.5 micro ns

*“ Ozone Health Watch ” means that the highest concentration of OZONE may approach the federal health standard.

“ PM-10 or PM-2.5 Health Watch ” means that the highest concentration of PM-10 or PM-2.5 may approach the federal health standard.

“ High Pollution Advisory ” means that the highest concentrati on of OZONE, PM-10, or PM-2.5 may exceed the federal health standard.

“ DUST ” means that short periods of high PM-10 concentrati ons caused by outflow from thunderstorms are possible. FORECAST

DATE

NOTICES

(*SEE BELOW

FOR DETAILS)

AIR POLLUTANT YESTERDAY

SAT 07/16/2011

OZONE HEALTH

WATCH

DUST

Highest AQI Reading/Site

(Preliminary data only) TODAY

SUN 07/17/2011

OZONE HEALTH

WATCH

DUST TOMORROW

MON 07/18/2011

OZONE HEALTH

WATCH

DUST EXTENDED

TUE 07/19/2011

OZONE HEALTH

WATCH

LIKELY/

OZONE HIGH

POLLUTION

ADVISORY

POSSIBLE

DUST



### O3* 87

TONTO NATIONAL

MONUMENT 90

MODERATE 97

MODERATE 100

MODERATE



### CO* 09

GREENWOOD 06

GOOD 07

GOOD 08

GOOD



### PM-10* 35

BUCKEYE 70

MODERATE 75

MODERATE 75

MODERATE



### PM-2.5* 30

PHOENIX SUPERSITE 48

GOOD 42

GOOD 44

GOODHealth message for Sunday, July 17: Unusually sensitive people should consider

reducing prolonged or heavy exertion outdoors.

Health message for Monday, July 18: Unusually sensitive people should consider

reducing prolonged or heavy exertion outdoors.

Synopsis and Discussion

OZONE: TODAY’S OZONE HEALTH WATCH HAS BEEN EXTENDED THRU MONDAY JULY 18

The synoptic weather pattern for today th ru Tuesday will feature a strong upper level high situated to the northeast of

Arizona. This location often yields a low-le vel easterly wind flow that tends to inhibit local ozone dispersion. At the

same time, afternoon high temperatures near 110 degrees F – forecasted to occur under mostly sunny skies – will

contribute to very efficient ozone producti on. Thus, ozone concentrations near or at unhealthy levels are expected the

next few days and as a result the Ozone Health Watch currently in effect has been extended thru at least Monday.

PARTICLES: The summer monsoon circulation pattern has resume d and for the Phoenix metro area this means a

slight chance for thunderstorms each day thru this forecast period. Gradient winds will be relatively light. Since last

week’s rainfall has reduced but not eliminated the risk fo r periods of dense blowing and/or transported dust generated

by outflow boundaries, there will be a mode rate risk for unhealthy PM-10 levels.

MONITORING SITE MAPS: STATIC MAP

- http://www.azdeq.gov/environ/air/monitoring/images/map.jpg

INTERACTIVE MAPS - http://aqwww.maricopa.gov/AirM onit oring/SitePollutionMap.aspx

http://www.airnow.gov /

POLLUTION MONITOR READINGS FOR SATURDAY, JULY 16, 2011



### O3 (OZONE)

Info on current 8-hour ozone standard: http://www.epa.gov/air/ozonepo llut ion/pdfs/2008_03_aqi_changes.pdf

For archived AQI maps go to: http://www.airnow.gov/index.cfm?action=airnow.maps

SITE NAME MAX 8-HR VALUE (PPB) MAX AQI AQI COLOR CODE

Alamo Lake (La Paz County) 53 45

Apache Junction (Pinal County) 65 67

Blue Point 63 61

Buckeye 48 41

Casa Grande (Pinal County) 55 47

Cave Creek 60 51

Central Phoenix 62 58

Dysart 51 43

Falcon Field 64 64

Fountain Hills 63 61

Glendale 59 50

Humboldt Mountain 57 48

North Phoenix 66 71

Phoenix Supersite 65 67

Pinal Air Park (Pinal County) 54 46

Pinnacle Peak 57 48

Queen Valley (Pinal County) 64 64

Rio Verde 59 50

South Phoenix 61 54

South Scottsdale 66 71

Tempe 60 51

Tonto Nat’l Mon. (Gila County) 71 87

West Chandler 62 58

West Phoenix 62 58

Yuma (Yuma County) 53 45

### CO (CARBON MONOXIDE)

SITE NAME MAX 8-HR VALUE (PPM) MAX AQI AQI COLOR CODE

Central Phoenix 0.7 08

Greenwood 0.8 09

Phoenix Supersite NOT AVBL NOT AVBL NOT AVBL

West Phoenix 0.4 05



### PM-10 (PARTICLES)

SITE NAME MAX 24-HR VALUE (ug/m3) MAX AQI AQI COLOR CODE

Buckeye 38 35

Central Phoenix 26 24

Combs School(Pinal County NOT AVBL NOT AVBL NOT AVBL

Durango 26 24

Dysart 18 17

Glendale 21 19

Greenwood 28 26

Higley 33 31

Maricopa (Pinal County) NOT AVBL NOT AVBL NOT AVBL

Phoenix Supersite 25 23

South Phoenix 35 32

West Chandler 27 25

West Forty Third 38 35

West Phoenix 34 31

Zuni Hills 18 17



### PM-2.5 (PARTICLES)

(Some data derived from light-scattering equipment)

For maps go to: http://www.airnow.gov /

SITE NAME MAX 24-HR VALUE (ug/m3) MAX AQI AQI COLOR CODE

Durango 7.0 23

Dysart 3.1 10

Estrella Mountain Park 5.4 18

Glendale 4.6 15

Phoenix Supersite 9.3 30

South Phoenix 4.6 15

Vehicle Emissions Lab 3.7 12

West Phoenix 5.3 17

### LOCAL AIR POLLUTANTS IN DETAIL

O3 (OZONE) :

Description – This is a secondary pollutant that is formed by the reaction of other primary

pollutants (precursors) such as VOCs (v olatile o rganic c ompounds) and NOx (N itrogen Ox ides)

in the presence of heat and sunlight.

Sources – VOCs are emitted from motor vehicles, chemical plants, refineries, factories, and

other industrial sources. NOx is emitted from motor vehicles, power plants, and other sources of

combustion.

Potential health impacts – Exposure to ozone can make people more susceptible to respiratory

infection, result in lung inflammation, and aggr avate pre-existing respiratory diseases such as

asthma. Other effects include decrease in lung fu nction, chest pain, and cough.

Unit of measurement – Parts per billion (ppb).

Averaging interval – Highest eight-hour period within a 24-hour period (midnight to midnight).

Reduction tips – Curtail daytime driving, refuel cars an d use gasoline-powered equipment as late

in the day as possible.

CO (CARBON MONOXIDE) :

Description – A colorless, odorless, poisonous gas formed when carbon in fuels is not burned

completely.

Sources – In cities, as much as 95 percent of all CO emissions emanate from automobile exhaust.

Other sources include industrial processes, non-transportation fuel combustion, and natural

sources such as wildfires. Pe ak concentrations occur in colder winter months.

Potential health impacts – Reduces oxygen delivery to the body’s organs and tissues. The health

threat is most serious for those who suff er from cardiovascular disease.

Unit of measurement – Parts per million (ppm).

Averaging interval – Highest eight-hour period within a 24-hour period (midnight to midnight)

Reduction tips – Keep motor vehicle tuned properly and minimize nighttime driving.

PM-10 & PM-2.5 (PARTICLES) :

Description – The term “particulate matter” (PM) includes both solid particles and liquid droplets

found in air. Many manmade and natural sources emit PM directly or emit other pollutants that

react in the atmosphere to form PM. Particles le ss than 10 micrometers in diameter tend to pose

the greatest health concern because they can be inhaled into and accumulate in the respiratory

system. Particles less than 2.5 micrometers in diameter are referred to as “fine” particles and are

responsible for many visibility degradations such as the “Valley Brown Cloud” (see

http://www.phoenixvis.net/ ). Particles with diameters between 2.5 and 10 micrometers are referred

to as “coarse”.

Sources – Fine = All types of combustion (motor vehicles, power plants, wood burning, etc.) and

some industrial processes. Coarse = crushing or grinding operations and dust from paved or

unpaved roads.

Potential health impacts – PM can increase susceptibility to respiratory infections and can

aggravate existing respiratory diseases, such as asthma and chronic bronchitis.

Units of measurement – Micrograms per cubic meter (ug/m3)

Averaging interval – 24 hours (midnight to midnight).

Reduction tips – Stabilize loose soils, slow down on dirt roads, carpool, and us e public transit.

{ Updated 03/23/2010 }

## APPENDIX C

NOTICE OF PUBLIC COMMENT PERIOD

### Request for Public Comments on Exception al Events in the Greater Phoenix Area

In 2005, Congress identified a need to account fo r events that result in exceedances of the

National Ambient Air Quality Standards (NAAQS) that are exceptional in nature (e.g., not

expected to reoccur or caused by acts of nature beyond man-made controls.) In response, EPA

promulgated the Exceptional Events Rule (EER) to address exceptional events in 40 CFR Parts

50 and 51 on March 22, 2007 (72 FR 13560). On May 2, 2011, EPA released draft guidance

documents on the implementation of the EER to Stat e, tribal and local air agencies for review.

The EER allows for states and tribes to “flag” air quality monitoring data as an exceptional

event. If flagged, these data can be excluded from consideration in air quality planning if EPA

concurs with the demonstration submitted by the flagging agency documenting that all

procedural and technical re quirements have been met.

Pursuant to 40 CFR 50.14(c)(3)(i) , the Arizona Department of E nvironmental Quality (ADEQ) is

soliciting comments on its final demonstrations of events that have caused elevated

concentrations of PM 10 

### in the Greater Phoenix area on February 19; July 18; August 3; August

18; August 25 through 28; September 2; Octobe r 4; November 4, 2011; January 21 – 22 and

February 27, 2012. ADEQ has decided to flag thes e episodes based on these analyses. Copies of

the demonstrations are available for review beginning Monday, December 3, 2012, on the ADEQ

website at www.azdeq.gov/environ/air/plan/ . Interested parties can submit written comments

throughout the comment period which will end at 5:00 p.m. on Tuesday, January 1, 2013. Any

comments received will be responded to and forwar ded to EPA with the final demonstrations.

Written comments should be addressed, faxed, or e-mailed to:

Andra Juniel, Air Assessment Section, Arizona Department of Environmental Quality, 1110 W.

Washington Street, 3415-A, Phoenix, AZ 85007, PHONE: (602) 771-4417; FAX: (602) 771-

2366, E-mail: juniel.andra@azdeq.gov.

In addition to being available on-line, copies of the analyses are available for review, Monday

through Friday, 8:30 a.m. to 4:30 p.m., at the ADEQ Records Center , 1110 W. Washington St.,

Phoenix, AZ, 85007, Attn: David Olivo, (602) 771-4380, email: olivo.david@azdeq.gov.

Persons with a disability may request reasonabl e accommodations by contacting Linda Morrison

at (602) 771-4793 or 1-800-234-5677 ext. 771-4793. Th is document is available in alternative

formats by contacting ADEQ TDD phone number at (602) 771-4829.

## A PPENDIX D

NATIONAL WEATHER SERVICE FORECASTS,

WARNINGS, AND ALERTS378

CDUS45 KPSR 190712

CLIPHX

CLIMATE REPORT

NATIONAL WEAT HER SERVICE PHOENIX AZ

1211 AM MST TUE JUL 19 2011

...................................

...THE PHOENIX AZ CLIMATE SUMMARY FOR JULY 18 2011...

CLIMATE NORMAL PERIOD 1971 TO 2000

CLIMATE RECORD PERIOD 1895 TO 2011

WEATHER ITEM OBSERVED TIME RECORD YEAR NORMAL DEPARTURE LAST

VALUE (LST) VALUE VALUE FROM YEAR

NORMAL

..................................................................

TE MPERATURE (F)

YESTERDAY

MAXIMUM 112 301 PM 115 1989 107 5 109

MINIMUM 90 627 AM 68 1946 84 6 89

1908

1899

AVERAGE 10 1 95 6

PRECIPITATION (IN)

YESTERDAY 0.00 1.04 1946 0.03

- 0.03 T

MONTH TO DATE 0.58 0.48 0.10 T

SINCE OCT 1 3.36 6.09

- 2.73 5.40

SINCE JAN 1 1.62 3.65

- 2.03 4.92

SNOWFALL (IN)

YESTERDAY 0.0

MONTH TO DATE 0.0

SINCE JAN 1 0.0

SINCE JUL 1 0.0

SNOW DEPTH 0

DEGREE DAYS

HEATING

YESTERDAY 0 0 0 0

MONTH TO DATE 0 0 0 0

SINCE JUN 1 0 0 0 0

SINCE JUL 1 0 0 0 0

COOLING

YESTERDAY 36 30 6 34

MONTH TO DATE 540 524 16 611

SINCE JUN 1 1323 1269 54 1405

SINCE JAN 1 2187 2064 123 2057

.... ..............................................................WIND (MPH)

HIGHEST WIND SPEED 31 HIGHEST WIND DIRECTION SE (140)

HIGHEST GUST SPEED 39 HIGHEST GUST DIRECTION SE (140)

AVERAGE WIND SPEED 8.9

SKY COVER

POSSIBLE SUNSHINE MM

AVERAGE SKY COVER 0.6

WEATHER CONDITIONS

THE FOLLOWING WEATHER WAS RECORDED YESTERDAY.

HAZE

SANDSTORM

RELATIVE HUMIDITY (PERCENT)

HIGHEST 37 600 AM

LOWEST 14 400 PM

AVERAGE 26

..........................................................

THE PHOENIX AZ CLIMATE NORMALS FOR TODAY

NORMAL RECORD YEAR

MAXIMUM TEMPERATURE (F) 107 116 1989

MINIMUM TEMPERATURE (F) 84 68 1913

1899

SUNRISE AND SUNSET

JULY 19 2011..........SUNRISE 532 AM MST SUNSET 737 PM MST

JULY 20 2011..........SUNRISE 532 AM MST SUNSET 736 PM MST

- INDICATES NEGATIVE NUMBERS.

R INDICATES RECORD WAS SE T OR TIED.

MM INDICATES DATA IS MISSING.

T INDICATES TRACE AMOUNT.

&&

.....................................................................

DEW POINT

HIGHEST DEW POINT MM

LOWEST DEW POINT MM

AVERAGE DEW POINT MM

.....................................................................

$$

855

FXUS65 KPSR 180200

AFDPSRAREA FORECAST DISCUSSION

NATIONAL WEATHER SERVICE PHOENIX AZ

700 PM MST SUN JUL 17 2011

.SYNOPSIS...

A FLOW ALOFT FROM THE SOUTHEAST IN THE CLOCKWIS E FLOW OF AIR AROUND

STRONG HIGH PRESSURE ALOFT OVER THE CENTRAL UNITED STATES WILL BRING

SOMEWHAT HIGHER HUMIDITY TO OUR AREA TONIGHT AND MONDAY. THIS MEANS

POSSIBLE DESERT BLOWING DUST AND A SLIGHT CHANCE OF THUNDERSTORMS IN

SOUTH

- CENTRAL AND SOUTHWE ST ARIZONA MAINLY IN THE LATE AFTERNOON AND

NIGHTTIME HOURS THROUGH TUESDAY. TEMPORARY DRYING IS EXPECTED FOR

MOST OF THE AREA LATE WEDNESDAY THROUGH THURSDAY INTO FRIDAY...

FOLLOWED BY MORE MOISTURE AND AN INCREASING CHANCE OF SHOWERS AND

THUNDERSTORM S NEXT WEEKEND.

&&

.DISCUSSION...

UPDATED THE HIGH AND LOW RESOLUTION FORECAST PRODUCTS TO BETTER

REFLECT THE EXPECTED WEATHER DURING THE REMAINDER OF THIS EVENING

AND THROUGH THE OVERNIGHT HOURS. 18.00Z KPSR SOUNDING IS VERY

STABLE...EVIDENT FROM THE AREA OF CONVECTION CROSSING PINAL COUNTY

THAT SEEMED TO HIT A BRICK WALL AS NEARED CASA GRANDE. SCATTERED

CONVECTION CONTINUES ACROSS FAR EASTERN ARIZONA...AND LOOKS TO HAVE

INCREASED A BIT IN COVERAGE THE PAST TWO HOURS. THIS IS BEING FORCED

BY TWO MID

- LEVEL LOWS /LARGER ONE OVER SONORA MX WITH ANOTHER NEAR

THE WHITE MOUNTAINS/. EXPECTING THE SONORA LOW TO LIFT NNW THROUGH

THE OVERNIGHT HOURS...WITH THE POSITIVE VORTICITY ADVECTION AND

MOISTURE ADVECTION AROUND 500 MB WE SH OULD SEE SOME

ISOLATED/SCATTERED CONVECTION DEVELOP AND MOVE THROUGH OUR CWA

THROUGH THE EARLY MORNING HOURS ON MONDAY.

PREVIOUS DISCUSSION...

ALTHOUGH MOST RAINFALL AMOUNTS ARE EXPECTED TO BE LESS THAN A

QUARTER OF AN INCH TONIGHT...SOME AMOUNTS OVER A QUARTER OF AN INCH

ARE EXPECTED IN SOUTH

- CENTRAL ARIZONA WITH THE BEST CHANCE

SOUTHEAST...EAST AND NORTHEAST OF PHOENIX. THERE IS ALSO A SLIGHT

CHANCE OF SHOWERS AND THUNDERSTORMS ACROSS SOUTHWEST ARIZONA TONIGHT

THROUGH MONDAY NIGHT...AND IN SOUTHEA ST CALIFORNIA MAINLY LATE

TONIGHT AND MONDAY MORNING.

DRIER AIR FROM THE SOUTHWEST IS EXPECTED TO TEMPORARILY MOVE OVER

MOST OF THE AREA INCLUDING THE GREATER PHOENIX AREA LATE WEDNESDAY

THROUGH THURSDAY INTO FRIDAY. THIS IS EXPECTED TO HAPPEN AS THE W EST

COAST LOW PRESSURE SYSTEM MOVES INLAND. THUS...HAVE CONFINED THE

POSSIBILITY OF ANY SHOWERS AND THUNDERSTORMS TO THE HIGHER TERRAIN

EAST OF THE GREATER PHOENIX AREA WEDNESDAY THROUGH DAYTIME FRIDAY.

IT IS STILL TOO EARLY TO TELL YET HOW CLOSE A TROPICAL STORM OR

POSSIBLY STRONGER WILL GET TO THE SOUTHERN TIP OF BAJA CALIFORNIA

LATE THIS COMING WEEK...FRIDAY OR SATURDAY. THIS SYSTEM BEARS

WATCHING IN TERMS OF THE AMOUNT OF MOISTURE THAT MAY MOVE INT O THE

SOUTHWESTERN UNITED STATES INCLUDING OUR AREA NEXT WEEKEND FOR A

SIGNIFICANT INCREASE IN SHOWERS AND THUNDERSTORMS.

FOR THE TIME BEING...HAVE BROUGHT BACK THE POSSIBILITY OF SHOWERSAND THUNDERSTORMS TO ALL OF SOUTH

- CENTRAL ARIZONA FRIDAY NIGHT.. .THEN

SPREAD THAT POSSIBILITY FROM SOUTH

- CENTRAL ARIZONA WEST TO THE LOWER

COLORADO RIVER VALLEY BY SATURDAY NIGHT...AND THE ENTIRE AREA FROM

SOUTH

- CENTRAL ARIZONA ACROSS SOUTHWEST ARIZONA AND SOUTHEAST

CALIFORNIA SUNDAY. AS WE GET CLOSER TO NEXT WEEKEN D AND EARLY NEXT

WEEK...WE WILL MOST LIKELY HAVE TO INCREASE THE CHANCE OF SHOWERS

AND THUNDERSTORMS FOR AT LEAST ONE OF THE LATE AFTERNOON AND

NIGHTTIME PERIODS...DURING THE WEEKEND AND EARLY NEXT WEEK.

&&

.AVIATION...

SOUTH

- CENTRAL ARIZONA INCLUDING KPHX AND KIWA...

DRY/STABLE ENVIRONMENT OVER PHOENIX THIS EVENING WHICH IS CRUSHING

CONVECTION AS IT APPROACHES FROM THE SOUTHEAST. OUTFLOW FROM THE SE

IS WASHING OUT RIGHT NOW...LIKELY NOT TO MAKE IT TO KPHX. BETTER

CONVECTION FURTHER EAST SHOULD HOLD SOMEWHAT CAUSING AN INCREASE IN

CLOUDS AND SOME

- SHRA DURING THE LATE EVENING THROUGH EARLY MORNING

HOURS. COULD SEE BETTER COVERAGE OF /WEAK/ CONVECTION ON MONDAY.

SOUTHEAST CALIFORNIA INCLUDING KIPL AND KBLH...

GENERALLY LIGHT WINDS WITH INCREASING MID/HIGH CLOUDS HEADING INTO

MONDAY MORNING. A STRAY SHOWER MAY WANDER TOWARD KBLH EARLY MONDAY

MORNING.

AVIATION DISCUSSION NOT UPDATED FOR AMENDED TAFS.

&&

.FIRE WEATHER...

WEDNESDAY THROUGH SUNDAY...

HIGH PRE SSURE CENTERED OVER THE CENTRAL UNITED STATES WILL SKIRT

FURTHER EAST IN RESPONSE TO AN UPPER LEVEL TROUGH APPROACHING THE

PACIFIC COAST. THIS WILL HELP TO SET UP A RETURN FLOW OF MONSOONAL

MOISTURE FROM THE GULF OF CALIFORNIA INTO ARIZONA...INCREASING THE

PROBABILITY OF MAINLY AFTERNOON AND EVENING SHOWERS. THE GREATEST

THREAT FOR STORMS LOOKS TO BE ON FRIDAY AND SATURDAY...WITH THE

BIGGEST THREATS BEING HEAVY RAINFALL...GUSTY SURFACE WINDS...AND

BLOWING DUST.

&&

.PSR WATCHES/WARNINGS/ADVISORIES..

.

AZ...NONE.

CA...NONE.

&&

$$

NATIONAL WEATHER SERVICE PHOENIX IS ON THE INTERNET AT

WEATHER.GOV/PHOENIX

DISCUSSION...INIGUEZ/ELLISAVIATION...INIGUEZ

FIRE WEATHER...MEYERS/MCLANE

339

FXUS65 KPSR 181003

AFDPSR

AREA FORECAST DISCUSSION

NATIONAL WEATHER SERVICE PHOENIX AZ

300 AM MST MON JUL 18 2011

.SYNOPSIS...

MEXICAN MONSOON MOISTURE HAS STARTED TO MOVE DEEPER INTO CENTRAL AND

EASTERN ARIZONA. A COUPLE OF WEAK WEATHER DISTURBANCES MOVING INTO

ARIZONA FROM MEXICO WILL INCREASE THE THR EAT FOR AFTERNOON AND

EVENING SHOWERS AND THUNDERSTORMS MAINLY OVER CENTRAL AND EASTERN

ARIZONA TODAY AND TUESDAY. A PACIFIC LOW PRESSURE SYSTEM MOVING

THROUGH THE WESTERN STATES NORTH OF ARIZONA WILL BEGIN TO PUSH THE

MONSOON MOISTURE EAST...INTO EASTERN ARIZONA WHERE MOST OF THE

THUNDERSTORM ACTIVITY WILL DEVELOP WEDNESDAY THROUGH FRIDAY. MONSOON

MOISTURE WILL PUSH BACK DEEPER INTO ARIZONA THIS WEEKEND FOR MORE

WIDESPREAD THUNDERSTORM COVERAGE THIS WEEKEND.

&&

DI SCUSSION...

MONSOON MOISTURE CONTINUED TO INCREASE FROM THE SOUTH...AND HAD

BECOME A LITTLE THICKER OVER SOUTHERN AZ DURING THE PREVIOUS 24

HOURS. AT THE SAME TIME...AN INVERTED TROF LOCATED SOUTHWEST OF EL

PASO TEXAS AT 07Z MON...SEEN THE BEST IN WATER VAPOR IMAGERY...

CONTINUED TO MOVE TOWARD AZ. A VERY NOTICEABLE UPPER LEVEL

DEFORMATION ZONE AHEAD OF THIS FEATURE...AND DEVELOPING OVER SOUTH

CENTRAL AZ...WILL CONTINUE TO PRODUCE A SLIGHT CHANCE OF SHOWERS

INTO THE MORNING HOURS. AT 08Z ONLY SPOTTY LIGHT SHOWERS WERE

DETECTED BY RADAR VICINITY PHOENIX...CASA GRANDE...AND OVER ZONE 24.

NO LIGHTNING. SOUTHEAST CA AND THE COLORADO RIVER VALLEY HAD MOSTLY

CLEAR SKIES.

THERE WAS ABSOLUTELY NO UPPER AIR DATA OVER A LARGE PORTION OF

NORTHWEST MEXICO... I.E. NO CHIHUAHUA NOR GUAYMAS SOUNDINGS LAST

EVENING...AND IS PERHAPS THE REASON WHY MODELS DIDNT INITIALIZE THE

INVERTED TROF SOUTHWEST OF EL PASO VERY WELL. THE EUROPEAN MODEL

CAME CLOSEST AND WE WILL PRETTY MUCH FOLLOW ITS KINEMATIC FLOW

REGIME AT A ND ABOVE 500 MB WITH A SLIGHT MODIFICATION.

THE MEXICAN INVERTED TROF WILL CONTINUE TO MOVE TOWARD THE NORTHWEST

AND INTO SOUTHERN AZ THIS AFTERNOON BUT IN A MUCH WEAKENED STATE.

WEAKNESS ALOFT COMBINED WITH INCREASED MOISTURE...AND FAIRLY STIFF

SOUTHEASTERLY MID LEVEL CONVECTIVE STEERING CURRENTS /10

- 15 KTS/...

CERTAINLY BODE WELL FOR AN ELEVATED THUNDERSTORM THREAT THIS

AFTERNOON AND EVENING. SINCE WE TALK IN PROBABILITY TERMS...THE

ABOVE ATMOSPHERIC PARAMETERS TODAY CONVEY AN ATYPICAL MONSOO N DAY

AND WARRANT THE ELEVATED CONVECTIVE THREAT...REPLETE WITH GUSTY

OUTFLOW WINDS AND A CHANCE OF DENSE BLOWING DUST ON THE DESERTS.

SOUTHEAST CA AND THE FAR SOUTHWEST AZ DESERTS VICINITY THE COLORADORIVER VALLEY WILL REMAIN DRY AND MORE STABLE ALO FT.

TUESDAY...

ANOTHER BUT VERY WEAK UPPER LEVEL PERTURBATION WILL FLOW INTO

CENTRAL AND SOUTHERN AZ FROM THE SOUTHWEST DIRECTION. MID LEVEL

CONVECTIVE STEERING CURRENTS OVER THE CENTRAL AZ DESERTS WILL

DECREASE TO LIGHT AND VARIABLE WINDS...BUT DEEP M ONSOON MOISTURE

REMAINS. IT APPEARS MOST CONVECTION TUESDAY AFTERNOON/EVENING WILL

DEVELOP OVER THE MOUNTAINS EAST OF PHOENIX AND IN SOUTHEAST AZ...

HOWEVER SINCE THERE IS SOME WEAKNESS ALOFT...CONVECTIVE OUTFLOW

BOUNDARIES AND POSSIBLE BOUNDARY COLLISI ONS COULD GENERATE EVENING

CONVECTION ON THE CENTRAL DESERTS BETWEEN CASA GRANDE AND PHOENIX.

AGAIN...SOUTHEAST CA AND THE FAR SOUTHWEST AZ DESERTS VICINITY THE

COLORADO RIVER VALLEY WILL REMAIN DRIER AND MORE DYNAMICALLY STABLE

ALOFT.

WEDNESDAY THROU GH FRIDAY...

A PACIFIC TROF PASSING THROUGH THE WESTERN STATES NORTH OF AZ WILL

BEGIN TO TREND THE WINDS ALOFT TO A MORE STABLE AND DRIER WEST AND

SOUTHWESTERLY DIRECTION. ONLY A SLIGHT CHANCE OF AFTERNOON AND

EVENING SHOWERS WILL EXIST EAST OF PHOENIX...BUT CONCENTRATED OVER

EASTERN AZ.

SATURDAY THROUGH MONDAY...

A COUPLE OF WELL DEFINED INVERTED TROFS IN THE MEXICAN EASTERLIES...

WILL BRUSH SOUTHEAST AZ THIS PERIOD. THIS WILL ENABLE MONSOON

MOISTURE TO PU SH BACK INTO AZ FOR AN ELEVATED CHANCE OF AFTERNOON

AND EVENING THUNDERSTORMS OVER CENTRAL AND EASTERN AZ.

&&

.AVIATION...

SOUTH

- CENTRAL ARIZONA INCLUDING KPHX AND KIWA...

DRY/STABLE ENVIRONMENT OVER PHOENIX THIS EVENING WHICH IS CRUSHING

CONVECTION AS IT APPROACHES FROM THE SOUTHEAST. OUTFLOW FROM THE SE

IS WASHING OUT RIGHT NOW...LIKELY NOT TO MAKE IT TO KPHX. BETTER

CONVECTION FURTHER EAST SHOULD HOLD SOMEWHAT CAUSING AN INCREASE IN

CLOUDS AND SOME

- SHRA DURING THE LATE EVENING THROUGH EARLY MORNI NG

HOURS. COULD SEE BETTER COVERAGE OF /WEAK/ CONVECTION ON MONDAY.

SOUTHEAST CALIFORNIA INCLUDING KIPL AND KBLH...

GENERALLY LIGHT WINDS WITH INCREASING MID/HIGH CLOUDS HEADING INTO

MONDAY MORNING. A STRAY SHOWER MAY WANDER TOWARD KBLH EARLY MONDAY

MO RNING.

AVIATION DISCUSSION NOT UPDATED FOR AMENDED TAFS.

&&

.FIRE WEATHER...

WEDNESDAY THROUGH SUNDAY...

HIGH PRESSURE CENTERED OVER THE CENTRAL UNITED STATES WILL SKIRT

FURTHER EAST IN RESPONSE TO AN UPPER LEVEL TROUGH APPROACHING THE

PACIFIC COAST. THIS WILL HELP TO SET UP A RETURN FLOW OF MONSOONAL

MOISTURE FROM THE GULF OF CALIFORNIA INTO ARIZONA...INCREASING THE

PROBABILITY OF MAINLY AFTERNOON AND EVENING SHOWERS. THE GREATESTTHREAT FOR STORMS LOOKS TO BE ON FRIDAY AND SATURDAY. ..WITH THE

BIGGEST THREATS BEING HEAVY RAINFALL...GUSTY SURFACE WINDS...AND

BLOWING DUST.

&&

.PSR WATCHES/WARNINGS/ADVISORIES...

AZ...NONE.

CA...NONE.

&&

$$

NATIONAL WEATHER SERVICE PHOENIX IS ON THE INTERNET AT

WEATHER.GOV/PHOENIX

DISCUSSION... VASQUEZ

AVIATION...INIGUEZ

FIRE WEATHER...MEYERS/MCLANE

176

FXUS65 KPSR 182252

AFDPSR

AREA FORECAST DISCUSSION

NATIONAL WEATHER SERVICE PHOENIX AZ

340 PM MST MON JUL 18 2011

.SYNOPSIS...

A FLOW ALOFT FROM THE SOUTHEAST IN THE CLOCKWISE FLOW OF AIR AROUND

STRONG HIGH PRESSURE ALOFT CENTERED OVER THE NATIONS MIDSECTION IS

BRINGING SOMEWHAT HIGHER HUMIDITY TO OUR AREA. THIS MEANS POSSIBLE

DESERT BLOWING DUST AND AT LEAST A SLIGHT CHANCE OF THUNDERSTORMS IN

SOUTH

- CENTRAL AND SOUTHWEST ARIZONA MAINLY IN THE LATE AFTERNOONS AND

EVENINGS THROUGH WEDNESDAY. TEMPORARY DRYING IS EXPECTED FOR MOST OF

THE AREA BY THURSDAY INTO FRIDAY...FOLLOWED BY A RETURN OF SOME

HUMIDITY AND AT LEAST A SLIGHT C HANCE OF THUNDERSTORMS MAINLY IN THE

LATE AFTERNOON AND NIGHTTIME HOURS THIS COMING WEEKEND AND EARLY NEXT

WEEK.

&&

.DISCUSSION...

A LINE OF THUNDERSTORMS WAS MOVING FROM SOUTHERN GILA COUNTY WEST

OVER NORTH

- CENTRAL PINAL COUNTY AND NORTHEAST MARICOPA COUNTY AT MID

AFTERNOON TODAY. IT WAS MOSTLY SUNNY WITH SOME CLOUDS WEST OF THERE

ACROSS THE REST OF SOUTH

- CENTRAL AND SOUTHWEST ARIZONA...AND SUNNY

OVER SOUTHEAST CALIFORNIA.

TEMPERATURES WERE GENERALLY CLOSE TO THE SAME TO A FEW DEGREE WARMER

TODAY COMPARED WITH THE SAME TIME YESTERDAY. IT WAS MORE HUMID TODAY

WITH DEW POINT TEMPERATURES GENERALLY 10 TO 20 DEGREES HIGHER EARLYTHIS AFTERNOON COMPARED WITH THE SAME TIME YESTERDAY. WIND WAS

GENERALLY FROM THE SOUTH AND SOUTHWEST 10 TO 20 MPH.. .EXCEPT STRONG

GUSTY AND VARIABLE NEAR THE THUNDERSTORMS.

THE CENTER OF VERY STRONG HIGH PRESSURE ALOFT CONTINUED OVER THE

NATIONS MIDSECTION TODAY. THE SOUTHWEST EXTENSION OF THIS HIGH

PRESSURE SYSTEM RESULTED IN ANOTHER HOT DAY IN OUR AREA TODAY WITH A

HIGH OF 112 DEGREES AT SKY HARBOR IN PHOENIX AS OF 301 PM MST. THIS

HIGH PRESSURE CENTER IS EXPECTED TO WEAKEN SOMEWHAT AND MOVE TO THE

SOUTHEASTERN UNITED STATES BY THURSDAY THROUGH SATURDAY.

A FLOW ALOFT FROM THE SOUTHEAST IN THE CLOCKWISE FLOW OF AIR AROUND

THE HIGH PRESSURE SYSTEM IS BRINGING SOMEWHAT HIGHER HUMIDITY MAINLY

TO SOUTH

- CENTRAL ARIZONA. LOW PRESSURE SYSTEMS IN THIS FLOW MEAN

POSSIBLE DESERT BLOWING DUST AND AT LEAST A SLIGHT CHANCE OF

THUNDERSTORMS IN SOUTH

- CENTRAL AND SOUTHWEST ARIZONA IN THE LATE

AFTERNOON AND EVENING HOURS AT LEAST THROUGH TUESDAY INTO WEDNESDAY.

ONE SUCH HIGH LEVEL LOW PRESSURE SYSTEM WAS CENTERED OVER FAR

SOUTHEAST ARIZONA AND MOVING NORTH NEAR THE NEW MEXICO BORDER TODAY.

HOWEVER...THERE ARE OTHER LESS D ISCERNIBLE SYSTEMS IN THE FLOW.

MOST OF WHAT THUNDERSTORMS ARE ABLE TO MOVE FROM THE HIGHER TERRAIN

INTO THE LOWER DESERT OF SOUTH

- CENTRAL ARIZONA THIS EVENING ARE

EXPECTED TO BE SOUTHEAST AND EAST OF PHOENIX. OTHERWISE...SOME GUSTY

OUTFLOW WINDS AND BLOWING DUST ARE EXPECTED TO BE THE MAIN RESULTS

OF THE THUNDERSTORMS ON THE LOWER SOUTH

- CENTRAL ARIZONA DESERT

INCLUDING THE GREATER PHOENIX AREA INTO THIS EVENING.

ANOTHER LOW PRESSURE SYSTEM CURRENTLY OVER THE SOUTHERN GULF OF

CALI FORNIA IS EXPECTED TO MOVE NORTH OVER SOUTHWEST AND

SOUTH

- CENTRAL ARIZONA TUESDAY NIGHT AND WEDNESDAY. THIS WILL BRING A

BETTER POSSIBILITY OF SHOWERS AND THUNDERSTORMS TO SOUTHWEST ARIZONA

TUESDAY NIGHT AND WEDNESDAY AS WELL AS SOUTH

- CENTRAL ARIZONA.

DRIER AIR FROM THE SOUTHWEST IS EXPECTED TO TEMPORARILY MOVE OVER

MOST OF THE AREA INCLUDING THE GREATER PHOENIX AREA THURSDAY INTO

FRIDAY. THIS IS EXPECTED TO HAPPEN AS A LOW PRESSURE SYSTEM FROM THE

GULF OF ALASKA MOVES INLAND OVER THE WESTERN UNITED STATES. THUS...

THE POSSIBILITY OF ANY SHOWERS AND THUNDERSTORMS IS CONFINED TO THE

HIGHER TERRAIN EAST OF THE GREATER PHOENIX AREA THURSDAY THROUGH

DAYTIME FRIDAY.

A RETURN OF SOME HUMIDITY AND AT LEAST A SLIGHT CHANCE OF

THUNDERSTORMS MAINLY IN THE L ATE AFTERNOON AND NIGHTTIME HOURS IS

EXPECTED THIS COMING WEEKEND AND EARLY NEXT WEEK. THIS IS EXPECTED

TO HAPPEN AS HIGH PRESSURE ALOFT BUILDS NEAR THE 4 CORNERS WITH A

FLOW ALOFT FROM THE SOUTHEAST BRINGING SOME MOISTURE FROM MEXICO

OVER OUR AREA IN THE CLOCKWISE FLOW AROUND THE HIGH PRESSURE SYSTEM.

&&

.AVIATION...

SOUTH

- CENTRAL ARIZONA INCLUDING KPHX AND KIWA...

ISOLATED SHOWERS AND STORMS DEVELOPING THIS AFTERNOON AND EVENING

ACROSS SOUTH

- CENTRAL ARIZONA. MOST ACTIVITY IS EXPECTED TO REMAIN

OVER THE HIGHER TERRAIN NORTH AND EAST OF THE PHOENIX METROPOLITAN

AREA WITH A SOME STORMS MOVING INTO THE LOWER DESERTS. OUTFLOWBOUNDARIES FROM ALL SHOWERS AND STORMS COULD RESULT IN GUSTY SURFACE

WINDS AND BLOWING DUST.

SOUTHEAST CALIFORNIA INCLUDI NG KIPL AND KBLH...

LIGHT WINDS WITH ONLY A FEW CLOUDS WILL EXTEND THROUGH THE PERIOD.

AVIATION DISCUSSION NOT UPDATED FOR AMENDED TAFS.

&&

.FIRE WEATHER...

THURSDAY THROUGH MONDAY...

HIGH PRESSURE MOVING TOWARDS THE EAST WILL ALLOW MONSOON MOISTURE T O

ENTER INTO THE SOUTHWEST...INCREASING THE PROBABILITY OF AFTERNOON

AND EVENING SHOWERS. RESULTING IN GUSTY WINDS...LOCALIZED DUST...AND

EXTENSIVE AREAS OF LIGHTNING.

&&

.PSR WATCHES/WARNINGS/ADVISORIES...

AZ...NONE.

CA...NONE.

&&

$$

NATIONAL WEATHER SERVICE PHOENIX IS ON THE INTERNET AT

WEATHER.GOV/PHOENIX

DISCUSSION...ELLIS

AVIATION...WATERS

FIRE WEATHER...WATERS/MCLANE

694

FXUS65 KPSR 190230

AFDPSR

AREA FORECAST DISCUSSION...UPDATED

NATIONAL WEATHER SERVICE PHOENIX AZ

730 PM MS T MON JUL 18 2011

.SYNOPSIS...

A FLOW ALOFT FROM THE SOUTHEAST IN THE CLOCKWISE FLOW OF AIR AROUND

STRONG HIGH PRESSURE ALOFT CENTERED OVER THE NATIONS MIDSECTION IS

BRINGING SOMEWHAT HIGHER HUMIDITY TO OUR AREA. THIS MEANS POSSIBLE

DESERT BLOWING DUST AND AT LEAST A SLIGHT CHANCE OF THUNDERSTORMS IN

SOUTH

- CENTRAL AND SOUTHWEST ARIZONA MAINLY IN THE LATE AFTERNOONS AND

EVENINGS THROUGH WEDNESDAY. TEMPORARY DRYING IS EXPECTED FOR MOST OF

THE AREA BY THURSDAY INTO FRIDAY...FOLLOWED BY A RETURN OF SOME

HUMIDITY AND AT LEAST A SLIGHT CHANCE OF THUNDERSTORMS MAINLY IN THE

LATE AFTERNOON AND NIGHTTIME HOURS THIS COMING WEEKEND AND EARLY NEXT

WEEK.&&

.DISCUSSION...

A NUMBER OF OUTFLOW BOUNDARIES MOVED THROUGH MARICOPA AND PINAL

COUNTIES THIS EVENING RESULTING IN SEVERAL DUST STORMS. A NUMBER OF

REPORTS WERE RECEIVED WITH VISIBILITY WELL BELOW CRITERIA /QUARTER

MILE OR LESS/. A CLUSTER OF STRONG STORMS DID DEVELOP OVER THE WEST

VALLEY AS A COUPLE OF THE BOUNDARIES COLLIDED...PR ODUCING LOCALIZED

STRONG WINDS AND HEAVY RAINFALL /HIGHEST MEASURED ON FLOOD CONTROL

DISTRICTS NETWORK WAS 0.91 INCHES/. THE VAST MAJORITY OF THE VALLEY

DID NOT GET RAIN THOUGH MOST AREAS DID GET VARYING DEGREES OF DUST.

REDUCED RAIN CHANCES FOR THE RE ST OF THE EVENING AS ACTIVITY IS

DECREASING AND WITHOUT THE OUTFLOW BOUNDARIES/LIFTING MECHANISMS THE

100 J/KG OF CIN WILL NOT BE OVERCOME TO RELEASE THE 300

- 500 J/KG OF

CAPE EVIDENT IN THE 19.00Z KPSR SOUNDING. HRRR MODEL HAS BEEN DOING

WELL SO FAR TO DAY WITH THE CONVECTION AND THE LATEST RUN AGREES WITH

T

- STORM COVERAGE DECREASING WITH SHOWERS STRAGGLING INTO THE EARLY

MORNING HOURS.

PREVIOUS DISCUSSION...

THE CENTER OF VERY STRONG HIGH PRESSURE ALOFT CONTINUED OVER THE

NATIONS MIDSECTION TODAY. T HE SOUTHWEST EXTENSION OF THIS HIGH

PRESSURE SYSTEM RESULTED IN ANOTHER HOT DAY IN OUR AREA TODAY WITH A

HIGH OF 112 DEGREES AT SKY HARBOR IN PHOENIX AS OF 301 PM MST. THIS

HIGH PRESSURE CENTER IS EXPECTED TO WEAKEN SOMEWHAT AND MOVE TO THE

SOUTHEASTERN UNITED STATES BY THURSDAY THROUGH SATURDAY.

ANOTHER LOW PRESSURE SYSTEM CURRENTLY OVER THE SOUTHERN GULF OF

CALIFORNIA IS EXPECTED TO MOVE NORTH OVER SOUTHWEST AND

SOUTH

- CENTRAL ARIZONA TUESDAY NIGHT AND WEDNESDAY. THIS WILL BRING A

BETTER POSSIBILITY OF SHOWERS AND THUNDERSTORMS TO SOUTHWEST ARIZONA

TUESDAY NIGHT AND WEDNESDAY AS WELL AS SOUTH

- CENTRAL ARIZONA.

DRIER AIR FROM THE SOUTHWEST IS EXPECTED TO TEMPORARILY MOVE OVER

MOST OF THE AREA INCLUDING THE GREATER PHOENIX AREA THURSDAY I NTO

FRIDAY. THIS IS EXPECTED TO HAPPEN AS A LOW PRESSURE SYSTEM FROM THE

GULF OF ALASKA MOVES INLAND OVER THE WESTERN UNITED STATES. THUS...

THE POSSIBILITY OF ANY SHOWERS AND THUNDERSTORMS IS CONFINED TO THE

HIGHER TERRAIN EAST OF THE GREATER PHOENIX A REA THURSDAY THROUGH

DAYTIME FRIDAY.

A RETURN OF SOME HUMIDITY AND AT LEAST A SLIGHT CHANCE OF

THUNDERSTORMS MAINLY IN THE LATE AFTERNOON AND NIGHTTIME HOURS IS

EXPECTED THIS COMING WEEKEND AND EARLY NEXT WEEK. THIS IS EXPECTED

TO HAPPEN AS HIGH PRESS URE ALOFT BUILDS NEAR THE 4 CORNERS WITH A

FLOW ALOFT FROM THE SOUTHEAST BRINGING SOME MOISTURE FROM MEXICO

OVER OUR AREA IN THE CLOCKWISE FLOW AROUND THE HIGH PRESSURE SYSTEM.

&&

.AVIATION...

SOUTH

- CENTRAL ARIZONA INCLUDING KPHX AND KIWA...

DUST WILL CONTINUE TO SETTLE AROUND THE PHX AREA DURING THE NEXT TWO

HOURS LEADING TO GRADUAL IMPROVEMENT IN VISIBILITY. TSTM ACTIVITY

FOR THE MOST PART IS OVER FOR THIS EVENING/TONIGHT THOUGH A SHOWEROR TWO WILL BE POSSIBLE OVERNIGHT. SOUTHEAST WINDS WILL GRADUAL

DECAY AND BECOME LIGHT BY 04Z/9 PM MST.

SOUTHEAST CALIFORNIA INCLUDING KIPL AND KBLH...

LIGHT WINDS WITH ONLY A FEW CLOUDS WILL EXTEND THROUGH THE PERIOD.

AVIATION DISCUSSION NOT UPDATED FO R AMENDED TAFS.

&&

.FIRE WEATHER...

THURSDAY THROUGH MONDAY...

HIGH PRESSURE MOVING TOWARDS THE EAST WILL ALLOW MONSOON MOISTURE TO

ENTER INTO THE SOUTHWEST...INCREASING THE PROBABILITY OF AFTERNOON

AND EVENING SHOWERS. RESULTING IN GUSTY WINDS...LOC ALIZED DUST...AND

EXTENSIVE AREAS OF LIGHTNING.

&&

.PSR WATCHES/WARNINGS/ADVISORIES...

AZ...NONE.

CA...NONE.

&&

$$

NATIONAL WEATHER SERVICE PHOENIX IS ON THE INTERNET AT

WEATHER.GOV/PHOENIX

DISCUSSION...INIGUEZ/ELLIS

AVIATION...INIGUEZ

FIRE WEATHER...WATERS/MCLANE

813

FPUS75 KPSR 182143

NOWPSR

SHORT TERM FORECAST

NATIONAL WEATHER SERVICE PHOENIX AZ

243 PM MST MON JUL 18 2011

AZZ023

- 182345

-

GREATER PHOENIX AREA

INCLUDING THE CITIES OF...BUCKEYE...CAREFREE...CAVE CREEK...

CHANDLER...F OUNTAIN HILLS...GILBERT...GLENDALE...MESA...PEORIA...

PHOENIX...SCOTTSDALE...SUN CITY...AND TEMPE

243 PM MST MON JUL 18 2011

.NOW...

STRONG WINDS FROM THUNDERSTORMS OVER PINAL COUNTY WILL ENTER

SOUTHEAST PORTIONS OF THE PHOENIX METRO AREA AFTER 3 PM. WIND S OF

30 TO 40 MPH ALONG WITH BLOWING DUST WILL AFFECT QUEEN CREEK AND EASTMESA. LOCAL VISIBILITIES BELOW 1 MILE CAN BE EXPECTED WITH LARGER AREAS

OF VISIBILITIES BELOW 3 MILES. MOTORISTS ARE ADVISED TO USE CAUTION

DUE TO SUDDENLY REDUCED VISIBILITIES.

$$

NATIONAL WEATHER SERVICE PHOENIX IS ON THE INTERNET AT

WEATHER.GOV/PHOENIX

AJ

805

WUUS55 KPSR 182205

SVRPSR

AZC021

- 182300

-

/O.NEW.KPSR.SV.W.0014.110718T2205Z

- 110718T2300Z/

BULLETIN

- EAS ACTIVATION REQUESTED

SEVERE THUNDERSTORM WARNING

NATIONAL WEA THER SERVICE PHOENIX AZ

305 PM MST MON JUL 18 2011

THE NATIONAL WEATHER SERVICE IN PHOENIX HAS ISSUED A

* SEVERE THUNDERSTORM WARNING FOR...

CENTRAL PINAL COUNTY IN SOUTH CENTRAL ARIZONA...

THIS INCLUDES THE CITY OF FLORENCE...

* UNTIL 400 PM MST

* AT 302 PM MST...NATIONAL WEATHER SERVICE METEOROLOGISTS DETECTED A

SEVERE THUNDERSTORM CAPABLE OF PRODUCING DAMAGING WINDS IN EXCESS

OF 60 MPH. IN ADDITION...DENSE BLOWING DUST MAY ACCOMPANY THIS

SEVERE STORM. THIS STORM WAS LOCATED 7 MILES SOUTH OF FLORENCE...

AND MOVING NORTHWEST AT 15 MPH.

* OTHER LOCATIONS IN THE WARNING INCLUDE BUT ARE NOT LIMITED TO SAN

TAN VALLEY AND MAGMA

LAT...LON 3289 11146 3320 11160 3326 11139 3307 11120

3304 11123

TIME...MOT...LOC 2205Z 149DEG 12KT 3295 11 134

$$

LEINS

280

WUUS55 KPSR 190106

SVRPSR

AZC013

- 190145

-

/O.NEW.KPSR.SV.W.0015.110719T0106Z

- 110719T0145Z/

BULLETIN

- EAS ACTIVATION REQUESTEDSEVERE THUNDERSTORM WARNING

NATIONAL WEATHER SERVICE PHOENIX AZ

606 PM MST MON JUL 18 2011

THE NATIONAL WEATH ER SERVICE IN PHOENIX HAS ISSUED A

* SEVERE THUNDERSTORM WARNING FOR...

CENTRAL MARICOPA COUNTY IN SOUTH CENTRAL ARIZONA...

THIS INCLUDES THE CITIES OF...GLENDALE...YOUNGTOWN...WADDELL...

SURPRISE...SUN CITY WEST...SUN CITY...PEORIA...EL MIRAGE...

* UNTIL 645 PM MST

* AT 605 PM MST...NATIONAL WEATHER SERVICE METEOROLOGISTS DETECTED A

SEVERE THUNDERSTORM CAPABLE OF PRODUCING DAMAGING WINDS IN EXCESS

OF 60 MPH. THIS STORM WAS LOCATED NEAR GLENDALE SPORTS COMPLEX...

OR NEAR YOUNGTOWN...AND MOVI NG NORTH AT 15 MPH.

* THE SEVERE THUNDERSTORM WILL CONTINUE TO MOVE THROUGH THE WEST

SIDE OF THE PHOENIX METRO AREA.

LAT...LON 3365 11247 3373 11215 3350 11214 3348 11230

TIME...MOT...LOC 0106Z 165DEG 13KT 3355 11227

$$

LEINS

891

WWUS55 KPSR 190 112

SVSPSR

SEVERE WEATHER STATEMENT

NATIONAL WEATHER SERVICE PHOENIX AZ

612 PM MST MON JUL 18 2011

AZC013

- 190145

-

/O.CON.KPSR.SV.W.0015.000000T0000Z

- 110719T0145Z/

MARICOPA AZ

612 PM MST MON JUL 18 2011

...A SEVERE THUNDERSTORM WARNING REMAINS IN EFFECT UNTIL 645 PM MST

FOR CENTRAL MARICOPA COUNTY...

AT 611 PM MST...A SEVERE THUNDERSTORM WAS REPORTED CAPABLE OF

PRODUCING DAMAGING WINDS IN EXCESS OF 60 MPH. THIS STORM WAS LOCATED

NEAR YOUNGTOWN...MOVING NORTH AT 15 MPH. SPOTTERS HAVE REPORTED

WINDS OF 50 MPH WITH THIS STORM ALONG WITH MINOR TREE DAMAGE.

OTHER LOCATIONS IN THE WARNING INCLUDE BUT ARE NOT LIMITED TO EL

MIRAGE...WADDELL...SUN CITY...SURPRISE...PEORIA AND SUN CITY WEST

PRECAUTIONARY/PREPA REDNESS ACTIONS...

REPORT SEVERE WEATHER TO THE NEAREST LAW ENFORCEMENT AGENCY. THEY

WILL RELAY YOUR REPORT TO THE NATIONAL WEATHER SERVICE FORECAST

OFFICE.&&

LAT...LON 3365 11247 3373 11215 3350 11214 3348 11230

TIME...MOT...LOC 0112Z 165DEG 13KT 3357 11228

$$

LEINS

792

WWUS55 KPSR 190120

SVSPSR

SEVERE WEATHER STATEMENT

NATIONAL WEATHER SERVICE PHOENIX AZ

620 PM MST MON JUL 18 2011

AZC013

- 190145

-

/O.CON.KPSR.SV.W.0015.000000T0000Z

- 110719T0145Z/

MARICOPA AZ

620 PM MST MON JUL 18 2011

...A SEVERE THUNDERSTORM WARNING REMAINS IN EFFECT UNTIL 645 PM MST

FOR CENTRAL MARICOPA COUNTY...

AT 618 PM MST...A SEVERE THUNDERSTORM WAS REPORTED CAPABLE OF

PRODUCING DAMAGING WINDS IN EXCESS OF 60 MPH. THIS STORM WAS LOCATED

NEAR YOUNGTOWN...MOVING NORTH AT 15 MPH. SPOTTERS CONTINUE TO REPORT

PEA SIZED HAIL AND GUSTY WINDS OVER 50 MPH.

OTHER LOCATIONS IN THE WARNING INCLUDE BUT ARE NOT LIMITED TO EL

MIRAGE...WADDELL...SUN CITY...SURPRISE...PEORIA AND SUN CITY WEST

PRECAUTIONARY/PREPAREDNESS ACTIO NS...

REPORT SEVERE WEATHER TO THE NEAREST LAW ENFORCEMENT AGENCY. THEY

WILL RELAY YOUR REPORT TO THE NATIONAL WEATHER SERVICE FORECAST

OFFICE.

&&

LAT...LON 3365 11247 3373 11215 3350 11214 3348 11230

TIME...MOT...LOC 0119Z 165DEG 13KT 3360 11228

$$

LEINS

710

WWUS55 KPSR 190144

SVSPSR

SEVERE WEATHER STATEMENT

NATIONAL WEATHER SERVICE PHOENIX AZ

644 PM MST MON JUL 18 2011AZC013

- 190154

-

/O.EXP.KPSR.SV.W.0015.000000T0000Z

- 110719T0145Z/

MARICOPA AZ

644 PM MST MON JUL 18 2011

...THE SEVERE THUNDERSTORM WARNING FOR CENTRAL MARICOPA COUNTY WILL

EXPIRE AT 645 PM MST...

THE STORM NEAR YOUNGTOWN WILL CONTINUE TO WEAKEN...HOWEVER GUSTY

WINDS MAY CONTINUE THROUGH 7 PM.

REPORT SEVERE WEATHER TO THE NEAREST LAW ENFORCEMENT AGENCY. TH EY

WILL RELAY YOUR REPORT TO THE NATIONAL WEATHER SERVICE FORECAST

OFFICE.

LAT...LON 3365 11247 3373 11215 3350 11214 3348 11230

TIME...MOT...LOC 0144Z 165DEG 13KT 3369 11231

$$

LEINS

058

WWUS75 KPSR 182129

NPWPSR

URGENT

- WEATHER MESSAGE

NATIONAL WEA THER SERVICE PHOENIX AZ

229 PM MST MON JUL 18 2011

AZZ028

- 182300

-

/O.NEW.KPSR.DS.W.0006.110718T2129Z

- 110718T2300Z/

NORTHWEST AND NORTH CENTRAL PINAL COUNTY

INCLUDING THE CITIES OF...APACHE JUNCTION...CASA GRANDE...

FLORENCE

229 PM MST MON JUL 18 2011

...DUST STORM WARNING IN EFFECT UNTIL 4 PM MST THIS AFTERNOON...

THE NATIONAL WEATHER SERVICE IN PHOENIX HAS ISSUED A DUST STORM

WARNING...WHICH IS IN EFFECT UNTIL 4 PM MST THIS AFTERNOON.

* AFFECTED AREA: NORTHERN PINAL COUNTY.

* LOCATIONS INCLUDE: Q UEEN VALLEY...SAN TAN VALLEY...APACHE

JUNCTION...COOLIDGE...AND FLORENCE.

* TIMING: STRONG WINDS MOVING WESTWARD WILL CREATE DENSE BLOWING DUST

THROUGH AT LEAST 3 PM WITH LINGERING POOR VISIBILITIES UNTIL ABOUT

4 PM.

* WINDS: 35 TO 45 MPH...MOSTLY FROM THE EAST.* VISIBILITY: LOCAL VISIBILITIES AT OR BELOW ONE QUARTER MILE WITH

LARGE AREAS BELOW 1 MILE.

* IMPACTS: POOR VISIBILITIES WILL CREATE HAZARDOUS DRIVING

CONDITIONS. AFFECTED ROADWAYS INCLUDE...BUT ARE NOT LIMITED TO...HIGHWAY

60...HI GHWAY 79...AND HIGHWAY 287.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

IF YOU ENCOUNTER BLOWING DUST OR BLOWING SAND ON THE ROADWAY OR SEE

IT APPROACHING...PULL OFF THE ROAD AS FAR AS POSSIBLE AND PUT YOUR

VEHICLE IN PARK. TURN THE LIGHTS ALL THE WAY OFF AND KEEP YOUR FOOT

OFF THE BRAKE PEDAL.

&&

$$

NATIONAL WEATHER SERVICE PHOENIX IS ON THE INTERNET AT

WEATHER.GOV/PHOENIX

765

WWUS75 KPSR 182339

NPWPSR

URGENT

- WEATHER MESSAGE

NATIONAL WEATHER SER VICE PHOENIX AZ

439 PM MST MON JUL 18 2011

.ANOTHER ROUND OF DENSE BLOWING DUST WILL MOVE ACROSS NORTHERN PINAL

COUNTY AND INTO THE PHOENIX AREA THIS AFTERNOON.

AZZ023

- 028

- 190100

-

/O.NEW.KPSR.DS.W.0007.110718T2339Z

- 110719T0100Z/

GREATER PHOENIX AREA

- NORTHWEST AND NORTH CENTRAL PINAL COUNTY

INCLUDING THE CITIES OF...MESA...PHOENIX...APACHE JUNCTION...

CASA GRANDE...FLORENCE

439 PM MST MON JUL 18 2011

...DUST STORM WARNING IN EFFECT UNTIL 6 PM MST THIS EVENING...

THE NATIONAL WEA THER SERVICE IN PHOENIX HAS ISSUED A DUST STORM

WARNING...WHICH IS IN EFFECT UNTIL 6 PM MST THIS EVENING.

* AFFECTED AREA: NORTHERN PINAL COUNTY AND EASTERN PORTIONS OF THE

PHOENIX METRO AREA.

* LOCATIONS INCLUDE: CASA GRANDE...COOLIDGE...FLORENCE... QUEEN

CREEK...MESA...GILBERT...CHANDLER...TEMPE...INTERSTATE 10...HIGHWAY

79...HUNT HIGHWAY.

* TIMING: BLOWING DUST WILL CONTINUE TO OVERSPREAD NORTHERN PINAL

COUNTY THROUGH 5 PM WITH LINGERING POOR VISIBILITIES UNTIL ABOUT 6PM. FOR THE PHOENIX A REA...DENSE BLOWING DUST WILL ENTER THE

SOUTHEAST VALLEY AT ABOUT 445 PM AND SPREAD OVER MAINLY EASTERN

PORTIONS OF THE METRO AREA UNTIL ABOUT 6 PM.

* WINDS: SOUTHEAST 30 TO 40 MPH.

* VISIBILITY: ONE QUARTER MILE OR LESS.

* IMPACTS: DANGEROUS DRIVING CONDITIONS DUE TO SUDDENLY POOR

VISIBILITIES.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

IF YOU ENCOUNTER BLOWING DUST OR BLOWING SAND ON THE ROADWAY OR SEE

IT APPROACHING...PULL OFF THE ROAD AS FAR AS POSSIBLE AND PUT YOUR

V EHICLE IN PARK. TURN THE LIGHTS ALL THE WAY OFF AND KEEP YOUR FOOT

OFF THE BRAKE PEDAL.

&&

$$

NATIONAL WEATHER SERVICE PHOENIX IS ON THE INTERNET AT

WEATHER.GOV/PHOENIX

360

WWUS75 KPSR 190000

NPWPSR

URGENT

- WEATHER MESSAGE

NATIONAL WEATHER SERVICE P HOENIX AZ

500 PM MST MON JUL 18 2011

.ANOTHER ROUND OF DENSE BLOWING DUST WILL MOVE ACROSS NORTHERN

PINAL COUNTY AND INTO MARICOPA COUNTY...INCLUDING THE PHOENIX AREA...THIS

AFTERNOON.

AZZ027

- 190200

-

/O.EXB.KPSR.DS.W.0007.000000T0000Z

- 110719T0200Z/

SOUTHWEST MARICOPA COUNTY

INCLUDING THE CITY OF...GILA BEND

500 PM MST MON JUL 18 2011

...DUST STORM WARNING IN EFFECT UNTIL 7 PM MST THIS EVENING...

THE NATIONAL WEATHER SERVICE IN PHOENIX HAS ISSUED A DUST STORM

WARNING...WHICH IS IN EFFECT UNTIL 7 PM MST THIS EVENING.

* AFFECTED AREA: SOUTHWEST MARICOPA COUNTY

* LOCATIONS INCLUDE: GILA BEND...INTERSTATE 8...HIGHWAY 85.

* TIMING: BLOWING DUST WILL OVERSPREAD SOUTHWEST MARICOPA COUNTYTHROUGH 630 PM WITH LINGERING POOR VISIBILITIES UNTIL ABOUT 7 PM.

* WINDS: EAST 25 TO 35 MPH.

* VISIBILITY: ONE QUARTER MILE OR LESS.

* IMPACTS: DANGEROUS DRIVING CONDITIONS DUE TO SUDDENLY POOR

VISIBILITIES.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

IF YOU ENCOUNTER BLOWING DUST OR BLOWING SAND ON THE ROADWAY OR

SEE IT APPROACHING...PULL OFF THE ROAD AS FAR AS POSSIBLE AND PUT

YOUR VEHICLE IN PARK. TURN THE LIGHTS ALL THE WAY OFF AND KEEP

YOUR FOOT OFF THE BRAKE PEDAL.

&&

$$

AZZ023

- 028

- 190100

-

/O.C ON.KPSR.DS.W.0007.000000T0000Z

- 110719T0100Z/

GREATER PHOENIX AREA

- NORTHWEST AND NORTH CENTRAL PINAL COUNTY

INCLUDING THE CITIES OF...MESA...PHOENIX...APACHE JUNCTION...

CASA GRANDE...FLORENCE

500 PM MST MON JUL 18 2011

...DUST STORM WARNING REMAINS IN EF FECT UNTIL 6 PM MST THIS

EVENING...

A DUST STORM WARNING REMAINS IN EFFECT UNTIL 6 PM MST THIS

EVENING.

* AFFECTED AREA: NORTHERN PINAL COUNTY AND EASTERN PORTIONS OF

THE PHOENIX METRO AREA.

* LOCATIONS INCLUDE: MESA...PHOENIX...APACHE JUNCTION...C ASA

GRANDE...FLORENCE

* TIMING: BLOWING DUST WILL CONTINUE TO OVERSPREAD NORTHERN PINAL

COUNTY AND THE PHOENIX AREA THROUGH 530 PM WITH LINGERING POOR

VISIBILITIES UNTIL ABOUT 6 PM.

* WINDS: SOUTHEAST 30 TO 40 MPH.

* VISIBILITY: ONE QUARTER MILE OR LESS.

* IMPACTS: DANGEROUS DRIVING CONDITIONS DUE TO SUDDENLY POOR

VISIBILITIES.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

IF YOU ENCOUNTER BLOWING DUST OR BLOWING SAND ON THE ROADWAY OR

SEE IT APPROACHING...PULL OFF THE ROAD AS FAR AS POSSIBLE AND PUT

YOUR VEHICLE IN PARK. TURN THE LIGHTS ALL THE WAY OFF AND KEEP

YOUR FOOT OFF THE BRAKE PEDAL.&&

$$

NATIONAL WEATHER SERVICE PHOENIX IS ON THE INTERNET AT

WEATHER.GOV/PHOENIX

800

WWUS75 KPSR 190100

NPWPSR

URGENT

- WEATHER MESSAGE

NATIONAL WEATHER SERVICE PHOENIX AZ

600 PM MST MON JUL 18 2011

.ANOTHER ROUND OF DENSE BLOWING DUST WILL MOVE ACROSS NORTHERN

PINAL COUNTY AND INTO MARICOPA COUNTY...INCLUDING THE PHOENIX

AREA...THIS AFTERNOON.

AZZ028

- 190200

-

/O. EXP.KPSR.DS.W.0007.000000T0000Z

- 110719T0100Z/

NORTHWEST AND NORTH CENTRAL PINAL COUNTY

INCLUDING THE CITIES OF...APACHE JUNCTION...CASA GRANDE...

FLORENCE

600 PM MST MON JUL 18 2011

...DUST STORM WARNING WILL EXPIRE AT 6 PM MST THIS EVENING...

THE DUST STORM WARNING WILL EXPIRE AT 6 PM MST THIS EVENING FOR

NORTHWEST PINAL COUNTY.

$$

AZZ022

- 190200

-

/O.EXB.KPSR.DS.W.0007.110719T0100Z

- 110719T0200Z/

NORTHWEST MARICOPA COUNTY

INCLUDING THE CITIES OF...BUCKEYE...NEW RIVER...WICKENBURG

600 PM MST MON JUL 18 2011

...DUST STORM WARNING IN EFFECT UNTIL 7 PM MST THIS EVENING...

THE NATIONAL WEATHER SERVICE IN PHOENIX HAS ISSUED A DUST STORM

WARNING...WHICH IS IN EFFECT UNTIL 7 PM MST THIS EVENING.

* AFFECTED AREA: NORTHWEST MARICOPA COUN TY

* LOCATIONS INCLUDE: BUCKEYE...NEW RIVER...WICKENBURG

* TIMING: THROUGH 7 PM.

* WINDS: EAST 25 TO 35 MPH.

* VISIBILITY: ONE QUARTER MILE OR LESS.

* IMPACTS: DANGEROUS DRIVING CONDITIONS DUE TO SUDDENLY POORVISIBILITIES.

PRECAUTIONARY/PREPAREDN ESS ACTIONS...

IF YOU ENCOUNTER BLOWING DUST OR BLOWING SAND ON THE ROADWAY OR

SEE IT APPROACHING...PULL OFF THE ROAD AS FAR AS POSSIBLE AND PUT

YOUR VEHICLE IN PARK. TURN THE LIGHTS ALL THE WAY OFF AND KEEP

YOUR FOOT OFF THE BRAKE PEDAL.

&&

$$

AZZ023

- 190200

-

/O.EXT.KPSR.DS.W.0007.000000T0000Z

- 110719T0200Z/

GREATER PHOENIX AREA

INCLUDING THE CITIES OF...BUCKEYE...MESA...PHOENIX

600 PM MST MON JUL 18 2011

...DUST STORM WARNING NOW IN EFFECT UNTIL 7 PM MST THIS

EVENING...

THE DUST STORM WARNING IS NOW IN EFFECT UNTIL 7 PM MST THIS

EVENING.

* AFFECTED AREA: WESTERN PORTIONS OF THE PHOENIX METRO AREA.

* LOCATIONS INCLUDE: BUCKEYE...MESA...PHOENIX

* TIMING: BLOWING DUST WILL CONTINUE TO OVERSPREAD THE PHOENIX AREA

THROUGH 7 PM.

* WINDS: SOUTH EAST 30 TO 40 MPH.

* VISIBILITY: ONE QUARTER MILE OR LESS.

* IMPACTS: DANGEROUS DRIVING CONDITIONS DUE TO SUDDENLY POOR

VISIBILITIES.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

IF YOU ENCOUNTER BLOWING DUST OR BLOWING SAND ON THE ROADWAY OR

SEE IT APPROACHING...PULL OFF THE ROAD AS FAR AS POSSIBLE AND PUT

YOUR VEHICLE IN PARK. TURN THE LIGHTS ALL THE WAY OFF AND KEEP

YOUR FOOT OFF THE BRAKE PEDAL.

&&

$$

AZZ027

- 190200

-

/O.CON.KPSR.DS.W.0007.000000T0000Z

- 110719T0200Z/

SOUTHWEST MARICOPA COUN TY

INCLUDING THE CITY OF...GILA BEND

600 PM MST MON JUL 18 2011

...DUST STORM WARNING REMAINS IN EFFECT UNTIL 7 PM MST THISEVENING...

A DUST STORM WARNING REMAINS IN EFFECT UNTIL 7 PM MST THIS

EVENING.

* AFFECTED AREA: SOUTHWEST MARICOPA COUNTY

* LO CATIONS INCLUDE: GILA BEND

* TIMING: BLOWING DUST WILL OVERSPREAD SOUTHWEST MARICOPA

COUNTY THROUGH 630 PM WITH LINGERING POOR VISIBILITIES UNTIL

ABOUT 7 PM.

* WINDS: EAST 25 TO 35 MPH.

* VISIBILITY: ONE QUARTER MILE OR LESS.

* IMPACTS: DANGEROUS DRIVING CONDITIONS DUE TO SUDDENLY POOR

VISIBILITIES.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

IF YOU ENCOUNTER BLOWING DUST OR BLOWING SAND ON THE ROADWAY OR

SEE IT APPROACHING...PULL OFF THE ROAD AS FAR AS POSSIBLE AND PUT

YOUR VEH ICLE IN PARK. TURN THE LIGHTS ALL THE WAY OFF AND KEEP

YOUR FOOT OFF THE BRAKE PEDAL.

&&

$$

NATIONAL WEATHER SERVICE PHOENIX IS ON THE INTERNET AT

WEATHER.GOV/PHOENIX

897

WWUS85 KPSR 182138

SPSPSR

SPECIAL WEATHER STATEMENT

NATIONAL WEATHER SERVICE PHOENIX AZ

238 PM MST MON JUL 18 2011

AZZ024

- 028

- 182215

-

PINAL AZ

238 PM MST MON JUL 18 2011

...SIGNIFICANT WEATHER ADVISORY...

THE NATIONAL WEATHER SERVICE IN PHOENIX HAS ISSUED A

SIGNIFICANT WEATHER ADVISORY FOR...

NORTH C ENTRAL PINAL COUNTY IN SOUTH CENTRAL ARIZONA

UNTIL 315 PM MST.AT 234 PM MST...NATIONAL WEATHER SERVICE METEOROLOGISTS DETECTED

STRONG THUNDERSTORMS NEAR FLORENCE JUNCTION AND QUEEN VALLEY. THE

STORMS WERE MOVING SLOWLY WESTWARD.

WIND GUSTS UP TO 55 MPH ARE EXPECTED WITH THIS STORM.

LOCATIONS IMPACTED INCLUDE...

FLORENCE...QUEEN VALLEY...AND RURAL NORTHERN PINAL COUNTY...

IN ADDITION TO VERY STRONG WINDS...DENSE BLOWING DUST IS POSSIBLE

ALONG WITH LOCALIZED BRIEF HEAVY RAINFALL. TAKE SHELTER INSI DE OF A

STURDY BUILDING UNTIL THE STORMS PASS.

LAT...LON 3298 11131 3295 11136 3295 11140 3346 11140

3335 11103 3318 11103

TIME...MOT...LOC 2135Z 180DEG 0KT 3316 11125

$$

AJ

531

WWUS85 KPSR 182212

SPSPSR

SPECIAL WEATHER STATEMENT

NATIONAL WEATHER SERVICE PHOENIX AZ

312 PM MST MON JUL 18 2011

AZZ023

- 024

- 028

- 182300

-

GILA AZ

- MARICOPA AZ

- PINAL AZ

312 PM MST MON JUL 18 2011

...SIGNIFICANT WEATHER ADVISORY...

THE NATIONAL WEATHER SERVICE IN PHOENIX HAS ISSUED A

SIGNIFICANT WEATHER A DVISORY FOR...

WEST CENTRAL GILA COUNTY IN EAST CENTRAL ARIZONA

NORTH CENTRAL PINAL COUNTY IN SOUTH CENTRAL ARIZONA

EAST CENTRAL MARICOPA COUNTY IN SOUTH CENTRAL ARIZONA

UNTIL 400 PM MST

AT 302 PM MST...NATIONAL WEATHER SERVICE METEOROLOGISTS DETECTED A

STRONG THUNDERSTORM 8 MILES NORTH OF QUEEN VALLEY...MOVING WEST AT 20

MPH.

WIND GUSTS UP TO 50 MPH ARE EXPECTED WITH THIS STORM...ALONG WITH

FREQUENT DANGEROUS LIGHTNING.

LOCATIONS IMPACT ED INCLUDE...

KINGS RANCH...

APACHE JUNCTION...

EAST MESA...

HIGLEY...QUEEN CREEK...

SOME UNSECURED OBJECTS WILL BE BLOWN AROUND...TREE LIMBS COULD BE

SNAPPED OFF...AND ISOLATED POWER OUTAGES WILL BE POSSIBLE. SEEK

SHELTER INDOORS UNTIL TH E STORM PASSES.

LOCALLY DENSE BLOWING DUST IS POSSIBLE. IF YOU ENCOUNTER BLOWING DUST

WHILE DRIVING...PULL OVER AS FAR OFF THE ROADWAY AS POSSIBLE AND

PARK. TURN OFF YOUR HEADLIGHTS AND KEEP YOUR FOOT OFF THE BRAKE.

LAT...LON 3335 11175 3385 11142 3347 1 1105 3311 11126

TIME...MOT...LOC 2212Z 111DEG 16KT 3343 11131

$$

WATERS

485

WWUS85 KPSR 182304

SPSPSR

SPECIAL WEATHER STATEMENT

NATIONAL WEATHER SERVICE PHOENIX AZ

404 PM MST MON JUL 18 2011

AZZ022>024

- 028

- 190000

-

GREATER PHOENIX AREA

- NORTHWEST AND NORTH CENTRAL PINAL

COUNTY

- NORTHWEST MARICOPA COUNTY

- SOUTHERN GILA/TONTO NF FOOTHILLS

404 PM MST MON JUL 18 2011

...AREAS OF BLOWING DUST POSSIBLE THROUGH RUSH HOUR...

AT 400 PM MST...NATIONAL WEATHER SERVICE METEOROLO GISTS DETECTED

GUSTY WINDS FROM DISSIPATING THUNDERSTORMS. THESE WINDS WILL RESULT

IN AREAS OF BLOWING DUST

$$

494

WWUS85 KPSR 182306 CCA

SPSPSR

SPECIAL WEATHER STATEMENT...CORRECTED

NATIONAL WEATHER SERVICE PHOENIX AZ

406 PM MST MON JUL 18 2011

AZZ022>024

- 028

- 190000

-

GREATER PHOENIX AREA

- NORTHWEST AND NORTH CENTRAL PINAL

COUNTY

- NORTHWEST MARICOPA COUNTY

- SOUTHERN GILA/TONTO NF FOOTHILLS

406 PM MST MON JUL 18 2011

...AREAS OF BLOWING DUST POSSIBLE THROUGH RUSH HOUR...

AT 400 PM MST...NATIONAL WEATHER SERVICE METEOROLOGISTS DETECTEDGUSTY WINDS FROM DISSIPATING THUNDERSTORMS. THESE WINDS WILL RESULT

IN AREAS OF BLOWING DUST WHICH WILL REDUCE VISIBILITIES TO 2 MILES.

SIGNIFICANT REDUCTIONS IN VISIBILITIES ARE NOT EXP ECTED...BUT USE

CAUTION IF TRAVELING DURING RUSH HOUR AND IF YOU ENCOUNTER BLOWING

DUST.

$$

LEINS

725

WWUS85 KPSR 190022

AWWPHX

AZZ023

- 190130

-

AIRPORT WEATHER WARNING FOR SKY HARBOR AIRPORT

NATIONAL WEATHER SERVICE PHOENIX AZ

522 PM MST MON JUL 18 2011

...AIRPORT WEATHER WARNING FOR SKY HARBOR AIRPORT IN EFFECT UNTIL

630 PM MST...

THE NATIONAL WEATHER SERVICE IN PHOENIX HAS ISSUED AN AIRPORT WEATHER

WARNING FOR SKY HARBOR AIRPORT FOR STRONG GUSTY WINDS.

A DUST STORM IS MOVIN G TOWARD THE AIRPORT...WHICH WILL DROP

VISIBILITY TO A HALF MILE OR LESS AND CAUSE WINDS TO GUST INTO THE 30

TO 40 KNOT RANGE FROM THE SOUTH.

$$

INIGUEZ

129

WWUS85 KPSR 190054

SPSPSR

SPECIAL WEATHER STATEMENT

NATIONAL WEATHER SERVICE PHOENIX AZ

554 PM MST MON JUL 18 2011

AZZ023

- 190145

-

MARICOPA AZ

554 PM MST MON JUL 18 2011

...SIGNIFICANT WEATHER ADVISORY...

THE NATIONAL WEATHER SERVICE IN PHOENIX HAS ISSUED A

SIGNIFICANT WEATHER ADVISORY FOR...

CENTRAL MARICOPA COUNTY IN SOUTH CENTRAL ARI ZONA

UNTIL 645 PM MST

AT 553 PM MST...NATIONAL WEATHER SERVICE METEOROLOGISTS DETECTED A

STRONG THUNDERSTORM NEAR GLENDALE...MOVING NORTH AT 15 MPH.WIND GUSTS UP TO 50 MPH ARE EXPECTED WITH THIS STORM.

LOCATIONS IMPACTED INCLUDE...

LUKE AFB...

YOUNGTOWN...

SUN CITY... EL MIRAGE AND WADDELL...

SURPRISE...

SUN CITY WEST...

LAT...LON 3367 11239 3369 11210 3348 11210 3337 11240

TIME...MOT...LOC 0054Z 165DEG 13KT 3353 11221

$$

LEINS

602

WWUS85 KPSR 190129

SPSPSR

SPECIAL WEATHER STATEMENT

NATIONAL WEATHER SERVICE PHOENIX AZ

629 PM MST MON JUL 18 2011

AZZ022

- 023

- 190215

-

MARICOPA AZ

629 PM MST MON JUL 18 2011

...SIGNIFICANT WEATHER ADVISORY...

THE NATIONAL WEATHER SERVICE IN PHOENIX HAS ISSUED A

SIGNIFICANT WEATHER ADVISORY FOR...

NORTH CENTRAL MARICOPA COUNTY IN SOUTH CENTRAL ARIZONA

UNTIL 715 PM MST

AT 626 PM MST...NATIONAL WEATHER SERVICE METEOROLOGISTS DETECTED A

STRONG THUNDERSTORM 9 MILES NORTH OF PHOENIX. THIS STORM WAS

DISSIPATING A ND PRODUCING GUSTY OUTFLOW WINDS AROUND 40 MPH.

LOCATIONS IMPACTED INCLUDE...

WITTMANN...

ANTHEM...

NEW RIVER...

SOME UNSECURED OBJECTS COULD BE BLOWN AROUND. SEEK SHELTER INDOORS

UNTIL THE STORM PASSES.

LOCALLY DENSE BLOWING DUST IS POSSIBLE. IF YOU ENCOUNTER BLOWING DUST

WHILE DRIVING...PULL OVER AS FAR OFF THE ROADWAY AS POSSIBLE AND

PARK. TURN OFF YOUR HEADLIGHTS AND KEEP YOUR FOOT OFF THE BRAKE.

LAT...LON 3371 11204 3380 11217 3373 11242 3353 11254

3398 11265 3398 11261 3390 11228 3392 112243396 11224 3404 11217 3405 11209

TIME...MOT...LOC 0128Z 180DEG 0KT 3367 11205

$$

LEINS