03 October 2013

Richard Payton

8P-AR

U.S. Environmental Protection Agency, Region VIII

1595 Wynkoop Street

Denver, CO 80202-1129

Dear Richard:

Enclosed is the Exceptional Event report for the high wind/blowing dust episode that occurred on April 16, 

2013 in Telluride, Colorado. Other areas in Colorado were also affected by this event, and documentation will 

be provided for those areas at a later date. Data for this event are flagged on AQS, as required. This report, and 

the analysis and data contained within it, clearly shows that this exceptional event passed the four required tests 

under 40 CFR 50.14 (3)(iv).

This report was made available for public comment on our website from August 30 through September 30, 

2013, and was also distributed to potentially interested parties. No external comments were received. Some 

non-substantiative and formatting changes were made to the report by the Air Pollution Control Division.

We respectfully request a review of this exceptional event report and concurrence by EPA on this natural high 

wind/blowing dust event.

Please let me know if you have any questions.

Sincerely,

Gordon E. Pierce

Program Manager

Technical Services Program

Air Pollution Control Division

cc. Deirdre Rothery, EPA

Lisa Clarke, APCD

Kaitlin Stabrava, APCD

Terry Furuli, APCD
Technical Support Document

for the April 16, 2013,

Telluride Exceptional Event

Prepared by the Technical Services Program

Air Pollution Control Division

Colorado Department of Public Health and 

Environment

October 1, 2013
1

Executive Summary

In 2005, Congress identified a need to account for 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 On May 2, 2011, in an attempt to clarify this rule, EPA released draft guidance documents on the 

implementation of the EER to State, tribal and local air agencies for review. 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 

demonstration submitted by the flagging agency.

Due to the semi-arid nature of parts of the state, Colorado is highly 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 24-hour PM10 NAAQS. This document contains 

detailed information about the large regional windblown dust event that occurred on April 16, 2013. The 

Colorado Department of Public Health and Environment (CDPHE) Air Pollution Control Division

(APCD) has prepared this report for the U.S. Environmental Protection Agency (EPA) to demonstrate that 

the elevated PM10 concentrations were caused by a natural event. 

On April 16, 2013, a powerful spring storm system caused multiple exceedances of the twenty-four hour 

PM10 NAAQS in west-central and southwest Colorado. These PM10 sample values include Telluride (265

μg/m3), Durango (419 μg/m3), Pagosa Springs (295 μg/m3), Alamosa Adams State College (237 μg/m3), 

and Mt. Crested Butte (187 μg/m3). For this report, the focus was on Telluride (08-113-0004). A report 

will be developed at a later date for other locations.

All of the noted April 16, 2013, twenty-four-hour PM10 concentrations were above the 99

th percentile 

concentrations for their locations. The statistical and meteorological data clearly shows that but for this 

regional high wind blowing dust event, Telluride would not have exceeded the 24-hour NAAQS on April 

16, 2013. 

Specifically, the high value in Telluride on April 16, 2013, was the consequence of strong southwesterly 

prefrontal winds in combination with dry conditions, which caused significant blowing dust across much 

of Arizona, northwest New Mexico, southeast Utah and southwest Colorado. Widespread restrictions to 

visibility occurred in southwest Colorado on that day.

EPA‘s June 2012 Draft Guidance on the Preparation of Demonstrations in Support of Requests to 

Exclude Ambient Air Quality Data Affected by High Winds under the Exceptional Events Rule states “the 

EPA will accept a threshold of a sustained wind of 25 mph for areas in the west provided the agencies 

support this as the level at which they expect stable surfaces (i.e., controlled anthropogenic and 

undisturbed natural surfaces) to be overwhelmed...” In addition, in both eastern and western Colorado it 

has been shown that wind speeds of 30 mph or greater and gusts of 40 mph or greater can cause blowing 

dust (see reference for the Technical Support Document for the January 19, 2009 Lamar Exceptional 

Event and Appendix A - Grand Junction, Colorado, Blowing Dust Climatology at the end of this 

document). For this blowing dust event, hourly wind speeds of 50 mph and gust to 66 mph were recorded 

in the area.

The Albuquerque, Flagstaff, and Grand Junction NWS Forecast Offices issue weather warnings and 

advisories for northeast Arizona, most of New Mexico, eastern Utah, and western and southwestern 

Colorado. The APCD also issued blowing dust advisories for April 16, 2013.
2

The blowing dust climatology for the Four Corners area indicates that the area can be susceptible to 

blowing dust when winds are high. Landform imagery shows that northeastern Arizona and southeastern 

Utah in particular have experienced a long-term pattern of wind erosion and blowing dust when winds 

have been southwesterly and blowing into western and southern Colorado. Forecast products from the 

Navy Aerosol Analysis and Prediction System model provide evidence for a widespread blowing dust 

event in the Four Corners states, suggesting that significant source regions for dust in Colorado are

located in arid regions of Arizona, New Mexico and Utah. NOAA HYSPLIT forward and backward 

trajectories provide clear supporting evidence that dust from desert regions of Arizona, northwest New 

Mexico and southeast Utah caused the PM10 exceedances measured across portions of west-central and 

southwest Colorado on April 16, 2013. 

MODIS and GOES satellite imagery show that the Painted Desert and Four Corners area in general were 

source regions for the blowing dust on April 16, 2013. This is consistent with the climatology for many 

dust storms in Colorado as described in the Grand Junction, Colorado, Blowing Dust Climatology report. 

The Drought Monitor map of the western U.S. for April 16, 2013, shows that soils across northeastern 

Arizona, most of Utah, and parts of western Colorado had below normal soil moisture. The observations

of winds above blowing dust thresholds and restricted visibilities in the areas of concern demonstrate that 

this is a natural event that cannot be reasonably controlled or prevented.

The Center for Snow and Avalanche Studies has been studying the effects of wind-blown desert dust from 

Arizona, New Mexico, and Utah on snowpack albedo and snowmelt in the San Juan Mountains of 

Colorado. The Center for Snow and Avalanche Studies lists April 16, 2013, as a Dust-on-Snow event for 

the 2012/2013 water year. In addition, the snow depth analysis illustrates that the mountains surrounding 

Telluride had 16 to 100 inches of snow cover in the hours before the dust storm of April 16, 2013. These 

data provide strong evidence that a widespread, regional, blowing dust event caused exceedances at these 

locations rather than local sources.

Friction velocities provide a measure of the near-surface meteorological conditions necessary to cause 

blowing dust. Friction velocities were high enough to sustain blowing dust over undisturbed soils in 

northern Arizona, northwest New Mexico, southeast Utah, and west-central and southwest Colorado

during this event.

The PM10 exceedance in Telluride on April 16, 2013, would not have occurred if not for the following: (a) 

dry soil conditions over northeast Arizona, northwest New Mexico, most of Utah, and parts of western 

Colorado with 30-day precipitation totals below the threshold identified as a precondition for blowing 

dust in northeastern Arizona; (b) a surface low pressure system and cold front that were associated with a 

strong upper-level trough that caused strong prefrontal surface winds over the area of concern; and (c) 

friction velocities over regions of northern Arizona, northwest New Mexico, and southeast Utah that were 

high enough to allow entrainment of dust from natural sources with subsequent transport of the dust to 

Colorado in strong winds. The PM10 exceedances at Telluride and other locations were due to an 

exceptional event associated with regional windstorm-caused emissions from erodible soil sources over a 

large area of northeast Arizona, northwest New Mexico, most of Utah, and parts of western Colorado. 

These sources are not reasonably controllable during a significant windstorm under abnormally dry or 

moderate drought conditions.

APCD is requesting concurrence on exclusion of the 265 μg/m3 PM10 value from Telluride (08-113-

0004) on April 16, 2013. (APCD will request concurrence on exclusion of other PM10 values taken 

on the same day at a later date.)
3

Table of Contents

1.0 Exceptional Events Rule Requirements............................................................................................................6

1.1 Procedural Criteria .......................................................................................................................................6

1.2 Documentation Requirements......................................................................................................................7

2.0 Meteorological analysis of the April 16, 2013, blowing dust event and PM10 exceedance – Conceptual 

Model and Wind Statistics................................................................................................................................8

3.0 Evidence-Ambient Air Monitoring Data and Statistics...................................................................................52

3.1 Event Summary..........................................................................................................................................52

3.2 Clear Causal Relationship ..........................................................................................................................56

3.4 No Exceedance But For the Event .............................................................................................................58

4.0 News and Credible Evidence ..........................................................................................................................60

5.0 Not Reasonably Controllable or Preventable: Local Particulate Matter Control Measures ............................74

6.0 Summary and Conclusions..............................................................................................................................79

7.0 References.......................................................................................................................................................81
4

Figures

Figure 1: 24-hour PM10 concentrations for April 16, 2013...........................................................................................9

Figure 2: Surface Analysis for 00Z April 16, 2013, or 5 PM MST April 15, 2013 ....................................................10

Figure 3: Surface Analysis for 12Z April 16, 2013, or 5 AM MST April 16, 2013 ...................................................10

Figure 4: Surface Analysis for 00Z April 17, 2013, or 5 PM MST April 16, 2013 ....................................................11

Figure 5: 700 mb 5 PM MST April 15, 2013 .............................................................................................................12

Figure 6: 700 mb 5 AM MST April 16, 2013.............................................................................................................12

Figure 7: 500 mb 5 PM MST April 15, 2013 .............................................................................................................13

Figure 8: 500 mb 5 AM MST April 16, 2013.............................................................................................................13

Figure 9: NARR analysis for April 15, 2013, showing wind speeds in knots ............................................................14

Figure 10: NARR analysis for April 16, 2013, showing wind speeds in knots. .........................................................15

Figure 11: NARR analysis for April 16, 2013, showing wind speeds in knots ..........................................................15

Figure 12: NARR analysis for April 16, 2013, showing wind speeds in knots. .........................................................16

Figure 13: Height of the mixed layer above mean sea level from the NARR at 11 PM MST April 15, 2013 ...........17

Figure 14: Height of the mixed layer above mean sea level from the NARR at 5 AM MST April 16, 2013.............18

Figure 15: Height of the mixed layer above mean sea level from the NARR at 11 AM MST April 16, 2013...........18

Figure 16: NCAR RAP Real-Time Weather Data sector surface analysis for 10:43 AM MST April 16, 2013.........20

Figure 17: NCAR RAP Real-Time Weather Data sector surface analysis for 1:43 PM MST April 16, 2013 ...........21

Figure 18: NCAR RAP Real-Time Weather Data sector surface analysis for 3:43 PM MST April 16, 2013 ...........22

Figure 19: NCAR RAP Real-Time Weather Data sector surface analysis for 5:43 PM MST April 16, 2013 ...........23

Figure 20: Weather observation stations for April 16, 2013, meteorological analysis...............................................24

Figure 21: NOAA HYSPLIT 12-hour forward trajectories for Arizona and New Mexico .......................................34

Figure 22: NOAA HYSPLIT 12-hour back trajectories for Telluride, CO . ..............................................................35

Figure 23: NAAPS forecasted dust concentrations for 11 AM MST April 16 (18Z April 16), 2013.........................37

Figure 24: Southwest Colorado snow depth for 5 PM MST April 15, 2013. .............................................................39

Figure 25: NOHRSC observing stations for April 16, 2013, meteorological analysis. ..............................................40

Figure 26: Telluride Ski Resort snow depth, 11 PM MST April 14, 2013 - 11 PM MST April 15, 2013..................41

Figure 27: El Diente Peak snow depth, 11 PM MST April 14, 2013 - 11 PM MST April 15, 2013. .........................41

Figure 28: Lizard Head Pass snow depth, 11 PM MST April 14, 2013 - 11 PM MST April 15, 2013. .....................42

Figure 29: Dust-on-Snow Deposition Events Log in study area at Red Mountain Pass, Colorado. ...........................43

Figure 30: MODIS Aqua satellite afternoon image of the Four Corners region on April 16, 2013. ..........................44

Figure 31: GOES visible satellite image for 2:45 PM MST (2145Z), April 16, 2013................................................45

Figure 32: AIRS Dust Score for April 16, 2013. ........................................................................................................46

Figure 33: Total precipitation in inches for March 2013. ...........................................................................................47

Figure 34: Total precipitation in inches for April 1- April 15, 2013. .........................................................................48

Figure 35: Drought conditions for the western United States at 5 AM MST April 16, 2013. ....................................49

Figure 36: 12km NAM friction velocities in meters/second at 11 AM MST April 16 (18Z April 16), 2013.............50

Figure 37: 12km NAM friction velocities in meters/second at 5 PM MST April 16 (00Z April 17), 2013. ..............51

Figure 38: Telluride PM10 Time Series........................................................................................................................54

Figure 39: Telluride PM10 Histogram.........................................................................................................................55

Figure 40: Telluride PM10 Box-whisper Plot..............................................................................................................55

Figure 41: Telluride PM10 Box-whisper Plot, Reduced Scale ....................................................................................56

Figure 42: Wind Speed (mph) Various Stations, 04/08/2013 – 04/23/2013...............................................................57

Figure 43: PM10 Concentrations, Affected Sites, 04/08/2013 – 04/23/2013...............................................................58

Figure 44: Monthly PM10 Percentile Plots..................................................................................................................59

Figure 45: June 2005 and August 2011 Google Earth views of Telluride Village ......................................................78
5

Tables

Table 1: Weather observations for Telluride, Colorado on April 16, 2013. ...............................................................25

Table 2: Weather observations for Cortez, Colorado on April 16, 2013. ...................................................................26

Table 3: Weather observations for Durango, Colorado on April 16, 2013. ................................................................27

Table 4: Weather observations for Kykotsmovi (Hopi), Arizona on April 16, 2013..................................................28

Table 5: Weather observations for Window Rock, Arizona on April 16, 2013..........................................................29

Table 6: Weather observations for Winslow, Arizona on April 16, 2013. .................................................................30

Table 7: Weather observations for Farmington, New Mexico on April 16, 2013. .....................................................31

Table 8: Weather observations for Gallup, New Mexico on April 16, 2013. .............................................................32

Table 9: April 16, 2013, Event Data Summary. ..........................................................................................................52

Table 10: April 16, 2013, Site Percentile (All Affected Sites). ..................................................................................53

Table 11: April 16, 2013, PM10 Evaluation by Month and Year. ................................................................................53

Table 12: Estimated Maximum Event PM10 Contribution – Telluride. ......................................................................59

Table 13: State Regulations Regulating Particulate Matter Emissions........................................................................74

List of Appendices

Appendix A- Grand Junction, Colorado, Blowing Dust Climatology January 24, 2012

Appendix B - Weather Warnings and Blowing Dust Advisories for April 16, 2013
6

1.0 Exceptional Events Rule Requirements

In addition to the technical requirements that are contained within the EER, procedural requirements must 

also be met in order for EPA to concur with the flagged air quality monitoring data. This section of the 

report lays out the requirements of the EER and discusses how the APCD addressed those requirements. 

1.1 Procedural Criteria

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

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

fulfills them. 

The Federal EER requirements include public notification that an event was occurring, the placement of 

informational flags on data in EPA’s Air Quality System (AQS), submission of initial event description, 

the documentation that the public comment process was followed, and the submittal of a demonstration 

supporting the exceptional events flag. ACPD has addressed all of these procedural and documentation 

requirements. 

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

APCD issued Blowing Dust Advisories for Western and South Central Colorado advising citizens of the 

potential for high wind/dust events on April 16, 2013. This area includes: Telluride, Alamosa, Durango, 

Pagosa Springs and Crested Butte. The advisories that were issued on April 16, 2013, can be viewed at: 

http://www.colorado.gov/airquality/forecast_archive.aspx?seeddate=04%2f16%2f2013 and are included 

in Appendix B. 

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

APCD and other applicable agencies in Colorado submit data into EPA’s AQS. Data from both filterbased and continuous monitors operated in Colorado are submitted to AQS. 

When APCD and/or another agency operating monitors in Colorado suspects that data may be influenced 

by an exceptional event, APCD and/or the other operating agency expedites analysis of the filters 

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

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

monitors into AQS after quality assurance is complete. 

If APCD and/or the applicable operating agency have determined a potential exists that the sample value 

has been influenced by an exceptional event, a preliminary flag is submitted for the measurement when 

the data is uploaded to AQS. The data are not official until they are certified by May 1st of the year 

following the calendar 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 initial event description by July 1 of calendar year 

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

In early 2011, APCD and EPA Region 8 staff agreed that the notification of the intent to flag data as an 

exceptional event would be done by submitting data to AQS with the proper flags and the initial event 

descriptions. This was deemed acceptable, since Region 8 staff routinely pull the data to review for 

completeness and other analyses.

On April 16, 2013, PM10 sample values greater than 150 μg/m3 were taken at multiple sites across 

southwestern Colorado during the high wind event that occurred that day. In addition to the monitor 

located in Telluride, these monitors included Durango, Pagosa Springs, Alamosa (at Adams State 
7

College), Crested Butte and Mt. Crested Butte. All of these monitors are operated by APCD in 

partnership with local operators.

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

50.14(c)(3)(iv)) 

APCD posted this report on the Air Pollution Control Division’s webpage for public review. APCD 

opened a 30-day public comment period on August 30, 2013. Email notification was also provided to 

local officials. Any comments received will be submitted to EPA, consistent with the requirements of 40 

CFR 50.14(c)(3)(iv).

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

At the close of the comment period, and after APCD has had the opportunity to consider any comments 

submitted on this document, APCD will submit this document, along with any comments received (if 

applicable), and APCD’s responses to those comments, to EPA Region VIII headquarters in Denver, 

Colorado. The deadline for the submittal of this demonstration package is June 30, 2016. 

1.2 Documentation Requirements

Section 50.14(c)(3)(iv) of the EER states that in order to justify excluding air quality monitoring data, 

evidence must be provided for the following elements: 

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

(1) the event affected air quality, 

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

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

natural event;

b. There is a clear causal relationship between the measurement under consideration and the 

event; 

c. The event is associated with a measured concentration in excess of normal historical 

fluctuations; and 

d. There would have been no exceedance or violation but for the event. 
8

2.0 Meteorological analysis of the April 16, 2013, blowing 

dust event and PM10 exceedance – Conceptual Model 

and Wind Statistics

On April 16 of 2013, a powerful spring storm system caused an exceedance of the twenty-four hour PM10

standard at multiple monitors in south-central and southwest Colorado, including Telluride which 

reported a concentration of 265 μg/m

3

. This high reading and other PM10 concentrations across Colorado 

are plotted on the map for April 16, 2013, in Figure 1. The exceedances were the consequence of high 

winds from an intense area of surface low pressure system combined with a vigorous cold front. These 

surface features were associated with a deep upper-level trough that was moving across the western 

United States. The surface winds were predominantly out of a south to southwesterly direction and 

moved over dry soils in northeast Arizona and northwest New Mexico producing significant blowing 

dust. This single storm system caused blowing dust during various time intervals on April 16, 2013, but 

was most prolific during the late morning and afternoon hours.

EPA’s June 2012, draft Guidance on the Preparation of Demonstrations in Support of Requests to 

Exclude Ambient Air Quality Data Affected by High Winds under the Exceptional Events Rule states “the 

EPA will accept a threshold of a sustained wind of 25 mph for areas in the west provided the agencies 

support this as the level at which they expect stable surfaces (i.e., controlled anthropogenic and 

undisturbed natural surfaces) to be overwhelmed...”. In addition, in both eastern and western Colorado 

it has been shown that wind speeds of 30 mph or greater and gusts of 40 mph or greater can cause 

blowing dust (see reference for the Technical Support Document for the January 19, 2009 Lamar 

Exceptional Event and Appendix A – Grand Junction, Colorado, Blowing Dust Climatology at the end of 

this document). For this blowing dust event, it has been assumed that sustained winds of 30 mph and 

higher or wind gusts of 40 mph and higher can cause blowing dust in northeast Arizona, northwest New 

Mexico and southwest Colorado.
9

Figure 1: 24-hour PM10 concentrations for April 16, 2013.

The surface weather associated with the storm system of April 16, 2013, is presented in Figure 2, Figure 

3 and Figure 4 - the surface analyses for 5 PM MST April 15, 2013, and 5 AM and 5 PM MST April 16, 

2013 respectively. Significant surface features during this period of time included a stationary front 

draped across southwest Colorado and southern sections of Utah and Nevada. Surface low pressure along 

this front strengthened and moved northeastward into central Colorado. A cold front also developed in 

the southwestern United States which eventually moved into southwest Colorado by the afternoon of 

April 16, 2013. 

The upper level trough associated with this storm system is shown in Figure 5 through Figure 8. Figure 

5 and Figure 6 show the 700-mb height analysis maps for 5 PM MST April 15, 2013, and 5 AM MST 

April 16, 2013, respectively, while Figure 7 and Figure 8 display the 500 mb height analysis maps for 

the same time period. The 700 mb level is roughly 3 kilometers above mean sea level (MSL) and the 500 

mb level is generally located approximately 6 kilometers above MSL. These four charts show that a deep 

trough of low pressure was present in the upper levels of the atmosphere preceding the blowing dust event 

of April 16, 2013, and that it was moving into the southwestern United States.
10

Figure 2: Surface Analysis for 00Z April 16, 2013, or 5 PM MST April 15, 2013.

(source: http://nomads.ncdc.noaa.gov/ncep/NCEP)

Figure 3: Surface Analysis for 12Z April 16, 2013, or 5 AM MST April 16, 2013.

(source: http://nomads.ncdc.noaa.gov/ncep/NCEP)
11

Figure 4: Surface Analysis for 00Z April 17, 2013, or 5 PM MST April 16, 2013.

(source: http://nomads.ncdc.noaa.gov/ncep/NCEP)
12

Figure 5: 700 mb (about 3 kilometers above mean sea level) analysis for 00Z April 16, 2013, or 5 PM 

MST April 15, 2013. 

(source: http://nomads.ncdc.noaa.gov/ncep/NCEP)

Figure 6: 700 mb (about 3 kilometers above mean sea level) analysis for 12Z April 16, 2013, or 5 AM 

MST April 16, 2013.

(source: http://nomads.ncdc.noaa.gov/ncep/NCEP)
13

Figure 7: 500 mb (about 6 kilometers above mean sea level) analysis for 00Z April 16, 2013, or 5 PM 

MST April 15, 2013.

(source: http://nomads.ncdc.noaa.gov/ncep/NCEP)

Figure 8: 500 mb (about 6 kilometers above mean sea level) analysis for 12Z April 16, 2013, or 5 AM 

MST April 16, 2013.

(source: http://nomads.ncdc.noaa.gov/ncep/NCEP)
14

Figure 9, Figure 10 and Figure 11 show the NARR (North American Regional Reanalysis) jet stream 

maximum winds rotating around the base of the 700 mb trough at 11pm MST April 15, 2013, and 5am 

and 11am MST April 16, 2013, respectively. At the 700 mb level, peak winds stretched from southern 

California northeastward into western New Mexico. This jet streak included a broad area of 40-60 knot 

winds located over the arid Four Corners region of Arizona, New Mexico, Utah and Colorado with the 

most intense wind bands over the Painted Desert of northeast Arizona. Figure 12 shows the 500 mb 

trough and corresponding wind speeds at 11am MST April 16, 2013. A very strong band of 500 mb 

winds near the base of the trough can once again be found over the Four Corners, ranging anywhere from 

60 to 100 knots.

Figure 9: NARR 700 mb analysis for 06Z April 16, 2013, or 11 PM MST April 15, 2013, showing wind 

speeds in knots.

(data source: http://nomads.ncdc.noaa.gov/data.php?name=access#hires_weather_datasets)
15

Figure 10: NARR 700 mb analysis for 12Z April 16, 2013, or 5 AM MST April 16, 2013, showing wind 

speeds in knots.

(data source: http://nomads.ncdc.noaa.gov/data.php?name=access#hires_weather_datasets)

Figure 11: NARR 700 mb analysis for 18Z April 16, 2013, or 11 AM MST April 16, 2013, showing 

wind speeds in knots.

(data source: http://nomads.ncdc.noaa.gov/data.php?name=access#hires_weather_datasets)
16

Figure 12: NARR 500 mb analysis for 18Z April 16, 2013, or 11 AM MST April 16, 2013, showing 

wind speeds in knots.

(data source: http://nomads.ncdc.noaa.gov/data.php?name=access#hires_weather_datasets)

The upper level trough (observed at both the 700 and 500 mb level) affected winds near the surface in two 

ways. First, it intensified a surface low-pressure system (shown in Figure 2 through Figure 4) with tight

pressure gradients which produced strong winds at the surface. Second, momentum associated with the 

strong winds aloft at the base of the trough was transferred to the surface because of deep vertical mixing 

in the area of the strong winds aloft. Figure 13, Figure 14 and Figure 15 show the height of the top of 

the mixed layer in kilometers above MSL at 11 PM MST on April 15, 2013, and 5 AM and 11 AM MST 

on April 16, 2013, respectively. In Figure 13 and Figure 14, mixing of 3 to 6 kilometers above MSL is 

located over the Four Corners. Mixing to this degree would have been sufficient to transfer momentum to 

the surface from the zone of strong winds at 700 mb located over the Four Corners during the same time 

frame (Figure 9 and Figure 10). By 11 AM MST on April 16, 2013, (Figure 15), mixing had increased 

significantly over the region to 5 to 7 kilometers above MSL. This magnitude of deep mixing would have 

allowed the transport of not only the strong 700 mb winds over the Four Corners shown in Figure 11, but 

also the very intense 500 mb winds shown in Figure 12 down to the surface. 

The combination of strong winds aloft, deep mixing and the tight pressure gradients associated with the 

surface low pressure system caused surface winds of up to 50 mph across the region with gusts to 66

mph. Winds of this strength can easily cause blowing dust if soils are dry. Recall that wind speeds of 30 

mph or greater and/or gusts of 40 mph or higher have been shown to cause blowing dust in Colorado (see 

reference for the Technical Support Document for the January 19, 2009, Lamar Exceptional Event and 

Appendix A - Grand Junction, Colorado, Blowing Dust Climatology at the end of this document). When 

blowing dust occurs with strong winds at the surface and aloft combined with deep mixing as was 

observed during the April 16, 2013, event, dust can be suspended for many hours and transported long 

distances. These conditions are the hallmarks of a regional dust transport event. 
17

The synoptic weather conditions on April 16, 2013, (illustrated in Figure 3 through Figure 15) show 

that the conditions necessary for widespread strong gusty winds and transport of blowing dust were in 

place over the area of concern.

Figure 13: Height of the mixed layer in kilometers above mean sea level from the NARR at 06Z April 

16, 2013, or 11 PM MST April 15, 2013.

(data source: http://nomads.ncdc.noaa.gov/data.php?name=access#hires_weather_datasets)
18

Figure 14: Height of the mixed layer in kilometers above mean sea level from the NARR at 12Z April 

16, 2013, or 5 AM MST April 16, 2013.

(data source: http://nomads.ncdc.noaa.gov/data.php?name=access#hires_weather_datasets)

Figure 15: Height of the mixed layer in kilometers above mean sea level from the NARR at 18Z April 

16, 2013, or 11 AM MST April 16, 2013.

(data source: http://nomads.ncdc.noaa.gov/data.php?name=access#hires_weather_datasets)
19

Figure 16 through Figure 19 present synoptic-scale weather maps centered over Denver, CO which include 

individual surface observations for 10:43 AM, 1:43 PM, 3:43 PM and 5:43 PM MST April 16, 2013, 

respectively. These maps cover Colorado and the areas of Arizona, Utah, and New Mexico that were 

upwind of the portions of Colorado that experienced exceedances of the PM10 standard. These surface 

analyses illustrate that winds above 30mph with gusts above 40 mph occurred in many areas both near the 

surface low pressure complex and south of the cold front shown in Figure 2 through Figure 4. 

On the map in Figure 16, the station observation for Farmington, NM (FMN) approximately 20 miles 

south of the Colorado state line in northwestern New Mexico shows a dollar sign ($). The dollar sign is 

the weather symbol for dust or sand raised by wind at the time of the observation. Within three hours 

(1:43 PM MST, Figure 17), several station plots in south-central and southwest Colorado indicated 

reduced visibilities and displayed the weather symbol of infinity (∞). The infinity sign is the weather 

symbol for haze. Haze is often reported during dust storms, and in dry and windy conditions, haze 

typically refers to blowing dust (see the following link for the description of haze published by the 

National Oceanic and Atmospheric Administration (NOAA): 

http://www.crh.noaa.gov/lmk/?n=general_glossary ). 

At 3:43 PM MST (Figure 18), Telluride (TEX) reported haze and a visibility of 5 statute miles (SM). 

Observations of haze continued for several hours in Telluride with the visibility hitting a low of 3 SM 

between 4:55 PM MST and 6:55 PM MST, including the observation displayed in Figure 19 (5:43 PM 

MST). Additional surface weather maps not included here show that haze and blowing dust were also 

reported in other parts of Arizona, New Mexico and Colorado on April 16, 2013. 

Surface weather maps show evidence of widespread blowing dust and winds above the threshold speeds 

for blowing dust on April 16, 2013.
20

Figure 16: NCAR RAP Real-Time Weather Data website DEN sector surface analysis for 1743Z April 

16, 2013, or 10:43 AM MST April 16, 2013.

(source: http://www.rap.ucar.edu/weather/)
21

Figure 17: NCAR RAP Real-Time Weather Data website DEN sector surface analysis for 2043Z April

16, 2013, or 1:43 PM MST April 16, 2013.

(source: http://www.rap.ucar.edu/weather/)
22

Figure 18: NCAR RAP Real-Time Weather Data website DEN sector surface analysis for 2243Z April 

16, 2013, or 3:43 PM MST April 16, 2013.

(source: http://www.rap.ucar.edu/weather/)
23

Figure 19: NCAR RAP Real-Time Weather Data website DEN sector surface analysis for 0043Z April 

17, 2013, or 5:43 PM MST April 16, 2013.

(source: http://www.rap.ucar.edu/weather/)

To build on the data from these synoptic maps, hourly surface weather observations were gathered from 

several reporting stations located in Colorado, New Mexico and Arizona for April 16, 2013. Figure 20

provides a reference map containing the locations of all the stations utilized for this analysis. Telluride is 

denoted in bold and caps.

Table 1 lists observations for the PM10 exceedance location of Telluride. Observations that are 

climatologically consistent with blowing dust conditions are highlighted in yellow. Table 2 through 

Table 8 contain the surface observations from sites that are in close vicinity to Telluride, or are in or near 

areas in northeast Arizona and northwest New Mexico that are known sources for blowing dust (see 

reference for Appendix A – Grand Junction, Colorado, Blowing Dust Climatology at the end of this 
24

document). At these locations sustained wind speeds were as high as 50 mph with wind gusts up to 66 

mph. Both of these values are well above the blowing dust thresholds already identified. 

Collectively these weather observation sites experienced many hours of reduced visibility along with 

sustained wind speeds and gusts at or above the thresholds for blowing dust. 

Observations of sustained wind speeds and gust speeds above the blowing dust thresholds and reduced 

visibilities on April 16, 2013, at weather stations in northeast Arizona, northwest New Mexico and 

southwest Colorado show that a regional dust storm event occurred under south to southwesterly flow

prior to a cold front passage. The observations contribute to the body of evidence that shows that a 

regional dust storm caused the PM10 exceedances at the monitoring sites in question.

Figure 20: Weather observation stations for April 16, 2013, meteorological analysis.
25

Table 1: Weather observations for Telluride, Colorado on April 16, 2013.

(source: http://www.met.utah.edu/mesowest/) 

Time 

MST 

April 16

Temperature 

Degrees F

Relative 

Humidity 

in %

Wind 

Speed 

in 

mph

Wind 

Gust in 

mph

Wind 

Direction 

in 

Degrees Weather

Visibility 

in miles

0:55 41 38 13 39 200 10

1:55 39 41 17 24 170 10

2:55 39 41 18 31 180 7

3:55 37 48 7 100 7

4:55 37 44 20 31 180 haze 5

5:55 37 38 25 35 170 7

6:55 37 38 24 38 170 10

7:55 41 36 12 38 210 10

8:55 43 31 17 43 150 7

9:55 45 33 13 37 180 7

10:55 46 34 9 30 130 10

11:55 48 29 23 38 180 10

12:55 50 23 29 53 180 10

13:55 52 22 22 38 210 7

14:55 52 22 24 47 180 7

15:55 52 17 15 41 180 haze 4

16:55 52 17 12 25 200 haze 3

17:55 50 18 14 21 200 haze 3

18:55 46 25 14 23 210 haze 3

19:55 45 26 9 20 210 haze 4

20:55 43 31 9 18 210 haze 5

21:55 41 41 15 28 190 7

22:55 41 36 20 36 200 10

23:55 39 41 10 32 150 10
26

Table 2: Weather observations for Cortez, Colorado on April 16, 2013.

(source: http://www.met.utah.edu/mesowest/) 

Time 

MST 

April 16

Temperature 

Degrees F

Relative 

Humidity 

in %

Wind 

Speed 

in mph

Wind 

Gust in 

mph

Wind 

Direction 

in 

Degrees Weather

Visibility 

in miles

6:53 50 34 4 10

7:53 55 26 22 28 190 10

8:53 59 22 27 36 190 10

9:17 61 20 28 37 200 haze 6

9:53 60 20 22 36 9

10:53 64 18 30 37 8

11:13 64 16 35 43 200 haze 2

11:17 64 16 33 43 190 haze 3

11:19 64 16 32 43 210 haze 2

11:24 64 18 22 40 210 haze 3

11:32 66 15 29 45 210 haze 2

11:41 64 16 28 38 200 haze 3

11:53 65 16 21 37 240 haze 6

12:48 68 13 35 44 200 haze 1.25

12:53 69 13 30 44 200 haze 1

12:58 70 13 25 39 210 haze 2

13:03 68 14 23 37 230 haze 3

13:14 70 12 31 38 210 haze 1.75

13:22 70 11 31 41 230 haze 1.25

13:24 68 11 27 41 230 haze 2

13:26 68 11 30 41 230 haze 3

13:53 68 11 21 41 220 haze 3

14:38 66 11 29 41 230 haze 2.5

14:53 68 11 29 41 230 haze 2.5

15:03 66 11 24 44 240 haze 2

15:10 66 12 28 37 240 haze 2

15:53 66 11 29 39 230 haze 2

16:06 64 12 30 40 230 haze 2

16:13 64 12 24 40 230 haze 2

16:28 64 12 24 38 230 haze 2

16:36 64 12 29 40 230 haze 2

16:53 64 12 30 43 230 haze 2.5

17:13 64 12 30 41 220 haze 2.5

17:21 64 12 29 40 230 haze 3

17:53 62 15 28 38 220 haze 4
27

Table 3: Weather observations for Durango, Colorado on April 16, 2013.

(source: http://www.met.utah.edu/mesowest/) 

Time 

MST 

April 16

Temperature 

Degrees F

Relative 

Humidity 

in %

Wind 

Speed 

in mph

Wind 

Gust in 

mph

Wind 

Direction 

in 

Degrees Weather

Visibility 

in miles

0:53 41 46 0 10

1:53 40 53 4 40 9

2:53 45 45 4 170 10

3:53 45 45 12 200 8

4:53 45 43 12 200 8

5:53 44 45 4 haze 6

6:53 46 43 6 150 8

7:53 51 39 17 23 190 10

8:53 54 34 18 35 210 10

9:53 57 30 17 28 190 8

10:53 59 25 22 33 220 haze 5

11:11 61 22 22 33 200 haze 5

11:53 63 19 21 36 200 haze 6

12:33 64 16 17 33 240 7

12:53 66 15 20 35 230 haze 5

13:25 66 13 23 40 240 haze 4

13:53 67 12 28 38 230 haze 5

14:00 66 12 31 41 210 haze 5

14:28 66 13 25 48 250

haze; 

squalls 6

14:36 66 12 24 43 220 haze 5

14:53 67 12 31 44 220 haze 5

15:25 66 11 27 47 230 haze 6

15:38 66 11 29 45 220 haze 6

15:53 66 11 23 37 240 haze 6

16:53 64 12 28 39 220 haze 6

17:53 62 12 18 39 240 haze 4

18:53 58 16 21 29 250 haze 3

19:53 54 22 16 22 250 haze 5

20:53 51 27 10 270 haze 6

21:53 50 29 10 260 haze 6

22:53 48 32 9 250 9

23:53 45 38 6 190 10
28

Table 4: Weather observations for Kykotsmovi (Hopi), Arizona on April 16, 2013.

(source: http://www.met.utah.edu/mesowest/) 

Time 

MST 

April 16

Temperature 

Degrees F

Relative 

Humidity 

in %

Wind 

Speed in 

mph

Wind 

Gust in 

mph

Wind 

Direction 

in 

Degrees Weather

Visibility 

in miles

0:13 53 39 27 36 199

1:13 51 36 28 44 202

2:13 50 42 27 41 199

3:13 50 46 23 41 217

4:13 49 41 21 33 214

5:13 48 41 23 31 199

6:13 48 42 27 40 199

7:13 50 40 21 40 214

8:13 53 36 26 34 199

9:13 57 30 26 37 204

10:13 59 24 32 41 222

11:13 60 23 25 43 226

12:13 62 21 22 35 234

13:13 64 20 27 39 224

14:13 64 19 30 46 232

15:13 64 18 29 43 227

16:13 62 15 29 44 237

17:13 60 18 29 42 235

18:13 58 21 24 39 239

19:13 53 21 22 36 232

20:13 50 20 18 29 222

21:13 47 27 13 23 261

22:13 44 31 11 19 273

23:13 41 40 11 16 336
29

Table 5: Weather observations for Window Rock, Arizona on April 16, 2013.

(source: http://www.met.utah.edu/mesowest/) 

Time 

MST 

April 16

Temperature 

Degrees F

Relative 

Humidity 

in %

Wind 

Speed 

in 

mph

Wind 

Gust in 

mph

Wind 

Direction 

in 

Degrees Weather

Visibility 

in miles

0:53 47 40 17 28 210 10

1:53 45 42 12 17 210 10

2:53 44 41 12 18 210 10

3:53 42 43 4 210 10

4:53 44 47 20 32 210 10

6:53 46 51 22 39 210 10

7:53 50 41 31 41 220 10

8:53 54 30 28 44 200 10

9:53 59 21 35 48 200 10

10:53 61 16 37 52 200 10

11:53 64 12 31 48 230 10

12:53 65 11 31 50 220 9

13:53 65 9 40 56 210 haze 6

14:53 66 9 32 47 230 10

15:53 64 10 30 48 230 10

16:53 62 13 32 47 220 10

17:53 59 16 28 41 220 10

18:53 54 20 16 32 210 10

19:53 51 21 18 38 210 10

20:53 50 24 25 39 230 10

21:53 47 42 13 240 10

22:53 45 49 16 22 250 10

23:53 43 45 7 260 10
30

Table 6: Weather observations for Winslow, Arizona on April 16, 2013.

(source: http://www.met.utah.edu/mesowest/) 

Time 

MST 

April 

16

Temperature 

Degrees F

Relative 

Humidity 

in %

Wind 

Speed 

in mph

Wind 

Gust in 

mph

Wind 

Direction 

in 

Degrees Weather

Visibility 

in miles

0:56 56 34 31 43 210 7

1:56 55 37 35 45 220 10

2:56 55 32 31 43 210 10

3:56 55 30 33 44 210 10

4:56 54 32 36 47 200 10

5:56 53 35 40 53 200 10

6:56 54 35 40 52 200 10

7:56 58 29 47 60 200 haze 5

8:56 62 22 47 61 200 haze 5

9:56 63 22 45 60 200 haze 3

10:56 65 17 50 62 210 haze 5

11:56 68 13 47 66 210 8

12:56 71 11 43 58 220 8

13:56 71 11 43 59 220 haze 5

14:56 70 13 43 60 220 9

15:56 70 13 45 59 200 10

16:56 69 17 37 52 190 10

17:56 67 19 43 51 210 10

18:56 63 23 33 46 220 10

19:56 59 29 29 40 210 10

20:56 56 35 16 220 10

21:56 53 41 10 220 10

22:56 51 42 10 270 10

23:56 48 47 6 250 10
31

Table 7: Weather observations for Farmington, New Mexico on April 16, 2013.

(source: http://www.met.utah.edu/mesowest/) 

Time 

MST 

April 

16

Temperature 

Degrees F

Relative 

Humidity 

in %

Wind 

Speed 

in mph

Wind 

Gust in 

mph

Wind 

Direction 

in Degrees Weather

Visibility 

in miles

7:53 56 34 24 31 190 9

8:53 60 28 17 28 190 9

9:03 61 27 16 24 190 8

9:53 65 21 22 28 220

haze; 

blowing dust 4

10:06 66 19 18 28 210

haze; 

blowing dust 6

10:13 66 18 23 31 210

haze; 

blowing dust 6

10:53 69 12 28 36 220

haze; 

blowing dust 4

11:53 73 8 30 39 240

haze; 

blowing dust 5

12:53 74 8 36 44 240

haze; 

blowing dust 3

13:53 75 8 29 41 220

haze; 

blowing dust 5

14:53 74 7 33 41 230 blowing dust 7

15:53 72 8 28 40 240

haze; 

blowing dust 6

16:17 72 7 30 37 230 blowing dust 7

16:53 70 6 28 39 240

haze; 

blowing dust 5

17:53 67 8 24 35 240 blowing dust 7

18:51 63 14 22 29 250

haze; 

blowing dust 4

18:53 63 13 18 29 250

haze; 

blowing dust 5

19:53 59 18 18 260 blowing dust 10

20:07 57 19 16 23 270 blowing dust 7

20:53 57 22 20 27 270

haze; 

blowing dust 6

21:53 54 28 17 25 270 blowing dust 8

22:19 54 28 17 24 270 blowing dust 9

22:53 53 32 17 270 blowing dust 10

23:53 49 34 7 240 blowing dust 10
32

Table 8: Weather observations for Gallup, New Mexico on April 16, 2013.

(source: http://www.met.utah.edu/mesowest/) 

Time 

MST 

April 16

Temperature 

Degrees F

Relative 

Humidity 

in %

Wind 

Speed 

in 

mph

Wind 

Gust in 

mph

Wind 

Direction 

in 

Degrees Weather

Visibility 

in miles

0:53 49 36 14 210 10

1:53 48 39 21 27 210 10

2:53 48 35 25 38 200 10

3:53 48 37 21 37 200 10

4:53 46 43 10 21 210 10

5:53 44 51 12 190 10

6:53 48 46 10 17 210 10

7:53 54 34 30 37 210 10

8:53 58 27 31 48 220 10

9:53 61 20 38 54 220 9

10:53 66 15 33 46 220 10

11:53 67 13 30 45 210 10

12:53 69 10 30 48 230 10

13:53 70 10 29 45 220 10

14:53 70 10 30 43 220 10

15:53 67 11 33 47 210 10

16:53 67 11 31 47 220 10

17:53 63 15 28 47 220 10

18:53 58 18 25 35 230 10

19:53 54 22 20 32 230 10

20:53 51 26 13 230 10

21:53 48 30 9 220 10

22:53 48 35 13 240 10

23:53 46 47 10 230 10

The Albuquerque, Flagstaff and Grand Junction National Weather Service (NWS) forecast offices issue 

weather warnings and advisories for northeast Arizona, most of New Mexico, eastern Utah and western 

and southwest Colorado. The weather warnings and advisories issued by theses offices for April 16, 

2013, are presented in Appendix B. Additionally, the Colorado Department of Public Health and 

Environment (CDPHE) issued a Blowing Dust Advisory on the morning of April 16, 2013, for a large 

portion of western and south-central Colorado, including Telluride. This advisory can also be found in 

Appendix B. 

Warnings and advisories issued by the NWS and CDPHE show that strong winds and areas of blowing 

dust were expected across this region on April 16, 2013.

Figure 21 shows the NOAA HYSPLIT 12-hour forward matrix trajectories (Draxler and Rolph, 2012) for 

northeast Arizona and northwest New Mexico starting at 5 AM MST April 16, 2013, (see the following 

link for more information on HYSPLIT from the NOAA Air Resources Laboratory: 

http://ready.arl.noaa.gov/HYSPLIT.php ). This analysis clearly shows the transport of air from these 

areas into southwest Colorado on April 16, 2013. HYSPLIT 12-hour back trajectories for 2 PM MST 

April 16, 2013, in Telluride (approximately when visibility started to deteriorate – see Table 1) are 
33

presented in Figure 22. This figure also visibly illustrates that Arizona and portions of northwest New 

Mexico were source regions for air transported into Telluride on April 16, 2013. 

NOAA HYSPLIT forward and backward trajectories provide clear supporting evidence that dust from 

arid regions of Arizona and northwest New Mexico caused the PM10 exceedances measured in 

Telluride, Colorado, on April 16, 2013.
34

Figure 21: NOAA HYSPLIT 12-hour forward trajectories for northeast Arizona and northwest New 

Mexico for 5 AM MST April 16 (12Z April 16), 2013, to 5 PM MST April 16, 2013.

(source: http://ready.arl.noaa.gov/HYSPLIT.php)
35

Figure 22: NOAA HYSPLIT 12-hour back trajectories for Telluride, CO for each hour from 2 AM MST 

April 16, 2013, to 2 PM MST April 16 (21Z April 16), 2013.

(source: http://ready.arl.noaa.gov/HYSPLIT.php)
36

Figure 23 shows the output for blowing dust from the Navy Aerosol Analysis and Prediction System 

(NAAPS) Global Aerosol Model for 11 AM April 16 (18Z April 16), 2013. The NAAPS system models 

blowing dust emissions and transport based on soil moisture content, soil erodibility factors and a variety 

of meteorological factors known to be conducive to blowing dust (for a description of NAAPS see: 

http://www.nrlmry.navy.mil/aerosol_web/Docs/globaer_model.html). 

The forecast panel in the lower left of Figure 23 shows an area of highly elevated surface dust 

concentrations over much of northeast Arizona, northwest New Mexico, southeast Utah and southwest 

Colorado. This model output suggests that the Four Corners region was a major source region for 

blowing dust on April 16, 2013. 

Forecast products from the Navy Aerosol Analysis and Prediction System model provide evidence for a 

widespread blowing dust event, suggesting that significant source regions for dust in Colorado were 

located in the arid Four Corners area.
37

Figure 23: NAAPS forecasted dust concentrations for 11 AM MST April 16 (18Z April 16), 2013.

(source: http://www.nrlmry.navy.mil/aerosolbin/aerosol/display_directory_all?DIR=/web/aerosol/public_html/globaer/ops_01/wus/)
38

The winter snow pack in the mountainous areas of southwest Colorado is often near its seasonal peak in 

April. The snow covers and moistens the soil which greatly reduces the potential for windblown dust 

from local sources. Figure 24 shows the snow depth analysis for southwest Colorado on April 15, 2013, 

at 5:00 PM MST. The snow depth analysis illustrates that the mountains surrounding Telluride had 16 to 

100 inches of snow cover in the hours before the dust storm of April 16, 2013. 

Individual station observations provide further evidence to the extent and depth of snow cover across the 

region. NOHRSC (National Operational Hydrologic Remote Sensing Center) observation stations were 

selected based on the prevailing wind direction in Telluride on April 16, 2013. With the wind 

predominantly out of a south to southwest direction during the dust event, stations located to the south 

and southwest of Telluride were analyzed including the Telluride Ski Resort, El Diente Peak and Lizard 

Head Pass. The precise locations of these stations and their proximity to the Telluride monitoring station 

are provided on the map in Figure 25. 

Figure 26 through Figure 28 present the snow cover measurements at Telluride Ski Resort, El Diente 

Peak and Lizard Head Pass respectively, for the time period of 11 PM MST April 14, 2013 – 11 PM MST 

April 15, 2013. Telluride Ski Resort which is located at 12,224 ft. above MSL and just a few miles to the 

south-southwest of the Telluride monitoring station reported 60-65 inches of snow cover. Meanwhile El 

Diente Peak and Lizard Head Pass are both located roughly 15-25 miles to the southwest of the Telluride 

monitor. Measurements at those locations show a snowfall depth in the 35-40 inch range. 

Snowpack and snow cover data for the mountains in southwest Colorado that were upwind from 

Telluride on April 16, 2013, demonstrate that blowing dust and elevated PM10 observed in Telluride 

were not likely to have been from local sources as the ground was covered in deep snow. Snow cover 

data provides strong evidence that a widespread, regional blowing dust event caused the exceedance at 

Telluride rather than local sources.
39

Figure 24: Southwest Colorado snow depth for 5 PM MST April 15, 2013.

(source: http://www.nohrsc.noaa.gov/interactive/html/map.html)
40

Figure 25: NOHRSC observing stations for April 16, 2013, meteorological analysis. 
41

Figure 26: Telluride Ski Resort snow depth, 11 PM MST April 14, 2013 - 11 PM MST April 15, 2013.

(source: http://www.nohrsc.noaa.gov/interactive/html/map.html)

Figure 27: El Diente Peak snow depth, 11 PM MST April 14, 2013 - 11 PM MST April 15, 2013.

(source: http://www.nohrsc.noaa.gov/interactive/html/map.html)
42

Figure 28: Lizard Head Pass snow depth, 11 PM MST April 14, 2013 - 11 PM MST April 15, 2013.

(source: http://www.nohrsc.noaa.gov/interactive/html/map.html)

The Center for Snow and Avalanche Studies has been studying the effects of wind-blown desert dust from 

Arizona, New Mexico and Utah on snowpack albedo and snowmelt in the San Juan Mountains of 

southwest Colorado for over 10 years. Figure 29 is the Center’s log of events that are associated with 

deposits or layers of wind-blown dust on or within the snowpack at the Senator Beck Basin Study area at 

Red Mountain Pass, which is approximately 6 miles to the southeast of Telluride. 

The Center for Snow and Avalanche Studies lists April 15-17, 2013 (highlighted in Figure 29) as a 

Dust-on-Snow event for a location in very close proximity to Telluride during the 2012/2013 water 

year. This provides clear supporting evidence that a regional blowing dust event with long-range 

transport caused the PM10 exceedance in Telluride, Colorado on April 16, 2013.
43

Figure 29: Dust-on-Snow Deposition Events Log at the Senator Beck Basin Study Area at Red Mountain 

Pass, Colorado.

(source: http://www.snowstudies.org/dust/SBBSA/summary_2013.html)

Figure 30 shows the MODIS Aqua satellite image for the Four Corners region of Arizona, New Mexico,

Utah and Colorado at approximately 12:50 PM MST (1950Z) April 16, 2013. Plumes of blowing dust are 

clearly visible originating in northwest New Mexico and the Painted Desert region of northeast Arizona. 

Those plumes extend to the northeast spreading dust into southwest Colorado and southeast Utah. Figure 

31 shows the GOES visible satellite imagery for the same general area at 2:45 PM MST (2145Z). This 

image illustrates the vast geographic extent of blowing dust in the region and the transport of this dust 

well into southwest Colorado.
44

Satellite-generated data products also indicate that a regional dust storm caused the PM10 exceedance in 

Telluride. Figure 32 displays the AIRS (Atmospheric Infrared Sounder) Dust Score for the Four Corners 

region on April 16, 2013 (see the following link for more information on Dust Score and other AIRS 

variables: http://disc.sci.gsfc.nasa.gov/nrt/data-holdings/airs-nrt-products/airs-nrt-products#WMS ). The 

tan to reddish brown colored pixels represent dust scores greater than 360, which is indicative of dust 

particles. Notice that much of the southwest corner of Colorado recorded a dust score in excess of 400. 

The interior non-shaded area over the San Juan Mountains (which includes at least part of Telluride 

proper) can be explained by cloud cover interference with the dust score algorithms. Figure 30 and 

Figure 31 both show cloud cover in the same general area as the zone of lower or missing dust scores in 

southwest Colorado. 

MODIS and GOES satellite imagery and derived products show that the Painted Desert and Four 

Corners area in general were source regions for blowing dust in southwest Colorado on April 16, 2013. 

This is consistent with the climatology for many dust storms in Colorado as described in the Grand 

Junction, Colorado, Blowing Dust Climatology report contained in Appendix A at the end of this 

document.

Figure 30: MODIS Aqua satellite afternoon image of the Four Corners region on April 16, 2013.

(source: http://ge.ssec.wisc.edu/modis-today/index.php)
45

Figure 31: GOES visible satellite image for 2:45 PM MST (2145Z), April 16, 2013.

(source: http://www.rap.ucar.edu/weather/satellite)
46

Figure 32: AIRS Dust Score for April 16, 2013.

(source: http://www.earthdata.nasa.gov/labs/worldview)

The Smoke Text Product from the National Oceanic and Atmospheric Administration (NOAA) Satellite 

Services Division - Descriptive Text Narrative for Smoke/Dust Observed in Satellite Imagery through 

1545Z April 16, 2013 (8:45 AM MST April 16, 2013) 

(http://www.ssd.noaa.gov/PS/FIRE/DATA/SMOKE/2013D161604.html) describes widespread dust 

across the Four Corners region on April 16, 2013:

“Very strong Swly winds are kicking up a large area of moderate dust/sand with numerous appox. 

1Km wide parallel bands with very dense conditions...particularly in AZ along the flats/canyon 

rim SW and NE of the Little Colorado River, from around Tuba City to Winslow; also in the 

Chinle Valley (particularly SW sources); and in NM along US-491 from Shiprock to Gallup. 

This dust and sand then covers all of SE Utah and SW Colorado, moving NNE and more N 

toward the frontal zone across N UT/SW WY, but becomes thinner the further from the sources.”

NOAA scientists with expertise in the analysis of dust storms have indicated that a regional dust storm 

in Arizona and New Mexico transported dust into southwest Colorado on April 16, 2013. 
47

Figure 33 shows the total precipitation in inches for the southwestern United States for March 2013. It 

shows that a large portion of northeast Arizona and northwest New Mexico received less than 0.5 inches 

of precipitation during March 2013. Additionally, it should be noted that precipitation of less than 0.5 

inches was reported in this region during the first half of April leading up to the April 16, 2013 dust event 

as evidenced in Figure 34. Combining the data from Figure 33 and Figure 34, we can extrapolate that a 

large portion of northeast Arizona and northwest New Mexico received 0.5 inches of precipitation or less 

during the March 1-April 15, 2013 time frame. This is an approximate precipitation threshold, below 

which, blowing dust can occur in the Painted Desert area when winds are above the blowing dust 

thresholds. This precipitation threshold is reported in Appendix A which shows that blowing dust can 

occur in northeastern Arizona source regions when soils are dry (typically less than 0.5 inches in a 30-day 

period at Hopi, Arizona) and winds are strong. 

Furthermore, the Drought Monitor report for the western United States as of 5:00 AM MST April 16, 

2013 (Figure 35) reveals that drought conditions in most of northeast Arizona and northwest New Mexico 

were categorized in the “Moderate” to “Extreme” range. Soils in the Four Corners area of northeast 

Arizona, northwest New Mexico and southeast Utah were dry enough to produce blowing dust when 

winds were above the thresholds for blowing dust.

Figure 33: Total precipitation in inches for March 2013.

(source: 

http://www.hprcc.unl.edu/maps/current/index.php?action=update_region®ion=WRCC).
48

Figure 34: Total precipitation in inches for April 1- April 15, 2013.

(source: 

http://www.hprcc.unl.edu/maps/current/index.php?action=update_region®ion=WRCC). 
49

Figure 35: Drought conditions for the western United States at 5 AM MST April 16, 2013.

(source: http://droughtmonitor.unl.edu/archive.html)

In a 1997 paper, “Factors controlling threshold friction velocity in semiarid and arid areas of the United 

States” (Marticorena et al., 1997), the authors characterized the erodibility of both disturbed and 

undisturbed desert soil types. The threshold friction velocity, which is described in detail in this paper, is 

a measure for conditions necessary for blowing dust and is higher for undisturbed soils and lower for 

disturbed soils. 

Friction velocities have been calculated for 11 AM MST April 16, 2013, and 5 PM MST April 16, 2013, 

using the 12km NAM (North American Mesoscale Model). These friction velocities are presented in 

Figure 36 and Figure 37, respectively. According to Marticorena and coauthors (1997), even undisturbed 

desert soils normally resistant to wind erosion will be susceptible to emission of blowing dust when 

threshold friction velocities are greater than about 1.0 to 2.0 meters per second. These figures show that a 

wide area of northern Arizona, western New Mexico and southwest Colorado had friction velocities 

above 1.0 meters per second during the late morning and afternoon hours of April 16, 2013. 

During the late morning of April 16, 2013, high friction velocity values were present in northwest New 

Mexico and within the Little Colorado River Valley and Painted Desert region of northeast Arizona 

(Figure 36). This is the same area where MODIS and GOES imagery clearly shows blowing dust

originating during the early afternoon hours (Figure 30 and Figure 31, respectively) and also where 30-

day precipitation totals were near or below 0.5 inches (Figure 33 and Figure 34). Note that blowing dust 

will typically only occur where friction velocities are high and the soils are dry and not protected by 

vegetation, forest cover, boulders, rocks, etc. This would tend to discount the possibility of dust from 
50

local sources in and near Telluride, but would reinforce the case that blowing dust originated in the desert 

and more arid sections of northeast Arizona and northwest New Mexico on April 16, 2013.

The elevated friction velocities shown in Figure 36 and Figure 37, the data on soil moisture conditions 

presented elsewhere in this report and the prevalence of winds above blowing dust thresholds (all 

occurring in traditional source regions in northeast Arizona and northwest New Mexico) prove that 

this dust storm was a natural event that was not reasonably controllable or preventable.

Figure 36: 12km NAM friction velocities in meters/second at 11 AM MST April 16 (18Z April 16), 

2013.

(data source: http://nomads.ncdc.noaa.gov/data.php?name=access#hires_weather_datasets)
51

Figure 37: 12km NAM friction velocities in meters/second at 5 PM MST April 16 (00Z April 17), 2013.

(data source: http://nomads.ncdc.noaa.gov/data.php?name=access#hires_weather_datasets)
52

3.0 Evidence-Ambient Air Monitoring Data and Statistics

3.1 Event Summary

On April 16, 2013, a strong upper atmospheric trough combined with an intensifying surface low pressure 

system and strong cold front moved across Colorado. During this interval PM10 sample values greater 

than 150 g/m3 were taken at multiple sites across southwestern Colorado, including Telluride (265

μg/m3), Durango (419 μg/m3), Pagosa Springs (295 μg/m3), Alamosa Adams State College (237 μg/m3), 

and Mt. Crested Butte (187 μg/m3). The high values were the consequence of strong southwesterly 

prefrontal winds beginning early on April 16, 2013, and extending through much of the day in 

combination with dry conditions which caused significant blowing dust across much of Arizona, 

northwest New Mexico, and southwest Colorado. The focus of this exceptional event document is for 

Telluride (08-113-0004). Additional documentation will be provided at a later date for other sites.

3.2 Historical Fluctuations of PM10 Concentrations in Telluride

This evaluation of PM10 monitoring data for sites affected by the April 16, 2013, event was made using 

valid samples from PM10 samplers from 2008 through available samples in 2013. APCD has been 

monitoring PM10 concentrations in these areas since 1985. Data in this analysis for sites affected by the 

event are from January 2008 through (generally) June of 2013. The overall data summary for the affected

sites is presented in Table 9, all data values are presented in g/m3:

Table 9: April 16, 2013, Event Data Summary.

Evaluation Alamosa ASC Pagosa Springs Crested Butte Mt. Crested Butte Durango Telluride

4/16/2013 237 295 140 187 419 265

Mean 24.1 23.7 24.6 16.5 21.5 18.3

Median 19 20 21 14 17 14

Mode 17 16 10 9 18 11

St. Dev. 27.1 21.2 17.3 12.3 26.2 22.5

Variance 735.9 450.6 299.7 150.8 688.4 508.1

Minimum 1 2 5 1 3 1

Maximum 440 349 174 187 419 354

Count 1775 1846 650 1926 632 626

As this table demonstrates the spatial scope of this event, addressed elsewhere in this document, was 

broad and had an impact on PM10 concentrations at multiple sites covering an extensive geographical 

area. Since this document will address only the sample in Telluride sample only that data set will be 

discussed in detail; APCD will submit additional documentation addressing samples affecting attainment 

status in Alamosa, Pagosa Springs, Mt. Crested Butte, and Durango at a later date. A snapshot summary 

of data from all those sites affected by the event is presented in Table 10, along with the approximate 

percentile value that data point represents for each site for their unique historical data sets, for the month 

of the event (every sample in any April), and for the year of the event. All percentile calculations 

presented in this section were made using the entire dataset, including known high wind events. There is 

no difference between the two datasets (with and without high wind events) in regards to percentile 

calculations. Percentile calculations for all sites affected by the event are presented in Table 10, only the 

sample in Telluride will be discussed in detail.
53

Table 10: April 16, 2013, Site Percentile (All Affected Sites).

Evaluation

Alamosa 

ASC

Pagosa 

Springs

Crested 

Butte

Mt. Crested 

Butte Durango Telluride

4/16/2013 237 295 140 187 419 265

Overall 99.6% 99.9% 99.8% Max Value Max Value 99.8%

All April 98.3% 99.4% 98.2% Max Value Max Value 98.2%

2013 Max Value Max Value Max Value Max Value Max Value Max Value

The Telluride sample of 265 g/m3is the largest sample in 2013 (through June), the second highest in any 

April and the second highest in the dataset. Additionally, the samples at Alamosa ASC, Pagosa Springs, 

Mt. Crested Butte and Durango are exceptional within their own datasets for any evaluation criteria. 

The overall magnitude and broad geographical extent of affected sites suggests that there was a 

common contribution to each sample from other than local sources.

Those data sets for sites with samples for which exclusion is being requested are further summarized by 

month. As with previous submittals these summaries the data presents no obvious ‘season’; PM10 levels 

at any particular site in Colorado do not necessarily fluctuate by season. Of greater importance affecting 

day-to-day, typical PM10 concentrations are local sources, e.g. road sanding and sweeping, local burning 

from agriculture and residential heating, vehicle contributions via road dust, unpaved lots or roads, etc. 

While the historic monthly mean values for the affected sites can be higher during the winter and spring 

months there is little month-to-month variation. Additionally, some of the sites exhibit monthly medians 

over these periods (winter and early spring) that are generally lower than other months of the year. This 

time frame (winter and early spring) is that which is most likely to experience the regional meteorological 

and dry soil conditions necessary for this type of event and are discussed elsewhere in this document. 

Although the maximum values for these months (winter and early spring) are the highest in the data set 

the ‘typical’ data (i.e. day-to-day, reflective of local conditions) are similar or lower than the same 

‘typical’ data for the rest of the year. The summary data for the month of April (all samples in any April 

from 2008 - 2013) and for 2013 for all affected sites are presented in Table 11:

Table 11: April 16, 2013, PM10 Evaluation by Month and Year.

Alamosa 

ASC

Pagosa 

Springs

Crested 

Butte

Mt. Crested 

Butte Durango Telluride

April 2013 April 2013 April 2013 April 2013 April 2013 April 2013

Mean 34.1 30.2 34.8 27.9 30.8 21.7 21.3 16 42 25.6 21.5 21.4

Median 19 21 23 21 23 18 16 13 18.5 18 18.5 15

Mode 16 10 23 13 12 7 12 12 13 18 14 11

St. Dev. 51.0 36.2 46.2 36.6 30.7 20.5 23.6 15.6 74.5 56.0 57.1 36.0

Variance 2599 1309 2133 1337 942 419 559 242 5548 3132 3262 1299

Minimum 1 4 2 3 6 6 1 4 6 5 3 3

Maximum 389 237 349 295 174 140 187 187 419 419 354 265

Count 174 141 169 157 57 51 168 155 58 52 58 51

The PM10 sample on April 16, 2013, at Telluride of 265 g/m3is the second largest sample recorded 

among all April samples, is the maximum value for all 2013 data, and is the second largest sample value
54

for the entire dataset. The one sample greater, 354 g/m3on April 05, 2010, is also associated with a high 

wind event. There are 2214 samples in this dataset. 

The sample of April 16, 2013, clearly exceeds the typical samples for this site.

The following plots graphically characterize the Telluride PM10 data and demonstrate the extent to which 

the event sample is exceptional. The first, Figure 38, is a simple time series; both samples in this dataset 

(2008 – 2013) greater than 150 g/m3is identified. Note the overwhelming number of samples 

occupying the lower end of the graph; an interested reader can count the number of samples greater than

100 g/m3. Of the 626 samples in this data set, less than 1% are greater than 100 g/m3.

Figure 38: Telluride PM10 Time Series.

Figure 39 is a simple histogram, demonstrating the overwhelming weight of samples on the low end of 

the curve. This range of data can be considered typical, representing contributions from local sources. 

Nearly 75% of the samples in this data set are less than 20 g/m3. Even in the highly variable months of 

winter and early spring over 90% of the samples are less than 50 g/m3. 

Clearly the sample of April 16, 2013, exceeds what is typical for this site.

354, 05 Apr 2010

265, 16 April 2013

0

50

100

150

200

250

300

350

400

29-Nov-07 28-Nov-08 28-Nov-09 28-Nov-10 28-Nov-11 27-Nov-12

Conce ntration (



g/m

3

)

Sample Date

Telluride PM10
55

Figure 39: Telluride PM10 Histogram.

The monthly box-whisker plot in Figure 40 highlights the consistency of the majority of data from month 

to month. Note the greater variability (wider inner-quartile range) and greater range of the data through 

the winter and early spring months that’s accompanied by typically greater monthly maxima. Recall, this 

time period experiences a greater number of days with meteorological conditions similar to those 

experienced on April 16, 2013. Although these high values affect the variability and central tendency 

(average) of the dataset they aren’t representative of what is typical at the site. 

Figure 40: Telluride PM10 Box-whisper Plot.

0.00%

10.00%

20.00%

30.00%

40.00%

50.00%

60.00%

70.00%

80.00%

90.00%

100.00%

0

5 0

100

150

200

250

300

Frequency

Concentration (g/m3)

Telluride PM10 Histogram

Frequency

Cumulative %

354, 05 Apr 2010

265, 16 Apr 2013

0

5 0

100

150

200

250

300

350

400

Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Concentration (g/m3

)

Month
56

The box-whisper plots graphically represent the overall distribution of each data set including the mean 

( ), the inner quartile range ( IQR, defined to be the distance between the 75th% and 25th%), the 

median (represented by the horizontal black line) and two types of outliers identifed in these plots: 

outliers greater than 75th% +1.5*IQR ( )and outliers greater than 75th% + 3*IQR ( ). The outliers 

that satisfy the last criteria and are greater than 150 g/m3are labeled with sample value and sample date. 

Each of these outliers is associated with a known high-wind event.

The presence of the extreme values distorts the graph, losing definition and distorting information 

presented across the range where the majority of data resides. The same plot graphed to 100 g/m3, 

which includes almost 99% of all the data, is presented in Figure 41. 

Figure 41: Telluride PM10 Box-whisper Plot, Reduced Scale.

Note the degree to which the data in early spring spring, including April, are skewed. The April mean 

(32.4 g/m3) is greater than the April 75th percentile value (29.5 g/m3). This is due to the presence of 

two extreme values and can create the perception that those months experiencing these high wind events 

are somehow ‘dirtier’ than other months of the year

The sample of April 16, 2013, clearly exceeds the typical data at this site.

3.2 Clear Causal Relationship

Wind speeds around the region (Southwest Colorado, Northeast Arizona, Northwest New Mexico) 

increased early in the morning of April 16, 2013, and stayed elevated through early morning of April 17,

2013, gusting to speeds in excess of 50 mph. The charts in Figure 42 display wind speed (mph) as a 

function of date from four widely dispersed stations throughout the region. Every one of these stations, 

despite being in completely disparate locations, exhibits nearly the same behavior in regards to the 

sustained high winds on April 16, 2013.

0

1 0

2 0

3 0

4 0

5 0

6 0

7 0

8 0

9 0

100

Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Concentration (g/m3

)

Month
57

Figure 42: Wind Speed (mph) Various Stations, 04/08/2013 – 04/23/2013.

Figure 43 plots PM10 concentrations from the affected sites in Colorado for the period for seven days prior 

to and following the sample(s) of April 16, 2013.

0

5

10

15

20

25

30

35

04/08/1304/10/1304/12/1304/14/1304/16/1304/18/1304/20/1304/22/1304/24/13

Wind Speed (mph)

Durango, CO (KDRO) Wind Speed, 4/8/13 - 4/23/13

0

5

10

15

20

25

30

35

40

04/08/1304/10/1304/12/1304/14/1304/16/1304/18/1304/20/1304/22/1304/24/13

Wind Speed (mph)

Pagosa Springs, CO (KPSO) Wind Speed, 4/8/13 - 4/23/13

0

10

20

30

40

50

60

04/08/1304/10/1304/12/1304/14/1304/16/1304/18/1304/20/1304/22/1304/24/13

Wind Speed (mph)

Winslow, AZ (KINW) Wind Speed, 4/8/13 - 4/23/13

0

5

10

15

20

25

30

35

40

45

04/08/1304/10/1304/12/1304/14/1304/16/1304/18/1304/20/1304/22/1304/24/13

Wind Speed (mph)

Alamosa, CO (KALS) Wind Speed, 4/8/13 - 4/23/13
58

Figure 43: PM10 Concentrations, Affected Sites, 04/08/2013 – 04/23/2013.

Figure 43 mimics the plots for wind speed, suggesting an association between the regional high winds and 

PM10 concentrations at the affected sites. Although not every sample in the region from April 16 is in 

excess of 150 elevated g/m3the elevated concentrations are clearly associated with the elevated wind 

speeds.

Given the spatial dislocation of the sites (meteorological and PM10) the relationship between the two 

data sets would suggest that the regional high winds had an effect on PM10 samples across a broad 

spatial region in Colorado.

3.4 No Exceedance But For the Event

Monthly percentile plots in Figure 44 demonstrate a high degree of association between monthly median 

values and relatively high monthly percentile values, e.g. the r2value between the Telluride monthly 90th 

percentile value and the Telluride monthly median is 0.82. As the percentile value decreases (i.e. 85%, 

75%, etc) the correlation between those values and the median increases sharply. The Telluride monthly 

percentile plot is presented in Figure 44:

0

5 0

100

150

200

250

300

350

400

450

04/08/1304/10/1304/12/1304/14/1304/16/1304/18/1304/20/1304/22/1304/24/13

Concentration (g/m3

)

PM10 Concentrations, Affected Sites Wind Speed, 4/8/13 - 4/23/13

Pagosa Springs

Crested Butte

Mt. Crested Butte

Durango

Telluride

Alamosa ASC
59

Figure 44: Monthly PM10 Percentile Plots.

It is certainly the case that monthly median values are indicative of typical, day to day concentrations. 

Additionally, there is a range of samples that are a product of normal variation subject to typical, day to 

day local effects. This range may be restricted to percentile values that are well correlated with the 

median. For the data set of concern in this document the percentile value that is reflective of typical, day 

to day variation is the 80th percentile value (r2= 0.92). Nearly all of the variation in the monthly 80th

percentile values of this data set can be explained by the variation in monthly median. In contrast, a 

reasonable estimate of the contribution to the event from local sources for these data sets may be the 

monthly 90th percentile values (r2 = 0.82). The portion of the sample concentration remaining from these 

monthly percentile values would be the sample contribution due to the event. Table 12 identifies various 

percentile values that are representative of the maximum contribution due to local sources from Telluride 

selected from all April data. In Table 12, the range estimate in the ‘Est. PM10 Contribution’ column is 

derived using the difference between the actual sample value and the 85th percentile as the minimum

(reasonable) event contribution estimate and the difference between the actual sample value and the 75th

percentile as the maximum (conservative) event contribution estimate. This column represents the range 

of estimated contribution to the April 16, 2013, Telluride sample from the high wind event. 

Table 12: Estimated Maximum Event PM10 Contribution – Telluride.

Site

Event Day 

Concentration 

(μg/m3)

April 

Median 

(μg/m3)

April 

Average 

(μg/m3)

April 

80th % 

(μg/m3)

April 

90th % 

(μg/m3)

Est. Conc. 

Above 

Typical 

(μg/m3)

Telluride 265 19 32.5 33 40 225 - 232

Clearly, there would have been no exceedance but for the additional contribution to the PM10 samples 

provided by the blowing dust event.

0

5 0

100

150

200

250

300

350

400

Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec

Concentration (g/m3

)

Month

Telluride PM1 0 Monthly Percentile Plot

Max

99th %

95th %

90th %

85th %

75th%

Median
60

4.0 News and Credible Evidence

Southwestern dust found in snow across Colorado

Author: Associated Press

POSTED: 11:30 AM MDT Apr 19, 2013

 Print

 Email



KTVI via CNN

DENVER -

Dust blown in from the Southwest settled on snow through much of Colorado during this week's storm and will eventually 

affect how fast the snowpack melts.

 

Researchers say it fell in Steamboat Springs, Fort Collins, Summit County, and the San Juan mountains. It was also seen in 

the Denver area.

 

Chris Landry of the Center for Snow and Avalanche Studies has been surveying the conditions for water providers. He said 

Friday that if more clean snow keeps falling, the impact of the dust will be delayed. However, he said once this week's snow 

layer and another deeper layer of dust from an April 8 storm are exposed, the snowmelt will accelerate because the dust 

absorbs sunlight.

 

NOAA (NOAH) researcher Jeffrey Deems compares the effect to wearing a dark t-shirt on a sunny day.
61

Contrasting webcam views of Abajo Peak: 

At1.:il;: Pc•,j I, !]h IJ:J..l':l K~JIQ"''JI ~~~.J~t l.dl'ff!O'IOI VIC A!~ tast'SOJt ... e,'!;t We-d U:t lt) 1210 ~J .illll ~urrrot WO.r.t"ef Temp ..'3.':1 •c. 1-i..Undlty: U% 

Sl.:~- r- l)(e ~lcunt,-. co IS ':·S r:Oe-; ScdhN'>t c 00 ~ t; re rr~5 SOJthe-ast S¥1 ).;.an 1-.\:Ult~ (I.) ~9 100 ~to the €.¥-t httemal Cameor 
62

Buena Vista webcam on April 16, 2013:

Montrose webcam on April 16, 2013:
63

Pagosa Springs webcam on April 16, 2013: 
64

CODOS 2013 Updates > Program WY 2013 Summary

COLORADO DUSTON-SNOW 

PROGRAM

WY 2013 

SUMMARY

Summary | Dust Log | Winter 

Storms and 

Wind | Snowpack| Melt 

Rate | Stream Flows | New 

and Ongoing 

Research |Program Funding

S U M M A R Y

Water Year 2013 entered late 

winter with dismal snowpack 

development at ten of eleven 

CODOS dust-on-snow monitoring sites, Willow Creek Pass being the single exception. Through March 2013, snowpack SWE totals at all other 

sites resembled or even fell short of the very dry winter of WY 2012, raising concerns about back-to-back drought seasons. That broadly 

consistent spatial pattern in scant precipitation began to diverge in April, 2013. CODOS sites in the northern Front Range and Colorado River 

headwaters benefitted most from a series of April and May winter storms that augmented snowpacks and eventually resulted in average or

even above average peak SWE levels on average or later-than-average dates. In the southwestern mountains, fewer and/or smaller April/May 

storms failed to offset the dry beginning to WY2013 winter. CODOS sites in the San Juan Mountains experienced, for the second year, 

substantially sub-par peak SWE values, on near-average dates. In between, the Central Mountains, Hoosier Pass, Park, and northern Gore 

ranges came closer to but still fell short of average snowpacks.

At the CSAS Senator Beck Basin Study Area at Red Mountain Pass, the primary CODOS monitoring site, WY2013 produced a total of ten separate 

dust-on-snow events, a lower total count than in the past three seasons. However, the actual mass of dust deposited at Senator Beck Basin in 

WY 2013 was greater than in any prior season, including the “Martian Winter” of WY 2009. Dust season began at Senator Beck Basin in 

November with a single event, February and March delivered four additional events, but the vast majority of dust deposition occurred 

during events D6 on April 8th and the long-duration D8 event of April 15-17. As of late March, dust layers observed at Senator Beck Basin 

were either weak or not present at CODOS sites farther north and east, creating some hope that WY 2013 might be dust-free in parts of the 

state. Then, dust events D6 and D8 spelled the end to that possibility with significant depositions statewide near the top of the snowpack.

http://snowstudies.org/dust/SBBSA/summary_2013.html
65

Good news of deep snow in Colorado foiled by dust that will speed 

melt

By Jason Blevins

The Denver Post

POSTED: 04/18/2013 06:08:40 PM MDT20 COMMENTS| UPDATED: 4 MONTHS AGO

The blessed snow that blanketed the high country and bolstered emaciated snowpacks this week was swirling with dirty trouble.

Little specks of Arizona, New Mexico and Utah rode in on the potentially record-setting 61-hour storm and promise to hasten 

snowmelt.

And then, below that fresh layer of sun-absorbing, snow-melting dust is an uncommonly dense layer from an April 8 dust storm —

the sixth of the season, or "D6" — that will send the snowmelt down in surging torrents, drowning hope for a sustained release deep 

into summer.

"None of the dust events we had last year were comparable to the April 8 event we had this year," said Chris Landry, executive 

director of the Center for Snow and Avalanche Studies in Silverton, who has studied dust events and the impact on snowpack in 

southern Colorado for the last decade.

The state has heralded recent storms that pushed snowpacks in every basin in the state beyond last year's record-low levels, floating 

hope that the still-growing snowpacks could dampen the impact of the sustained drought. But the dust storms — eight so far this 

year and more possibly on the way — will melt this year's snow faster than last year's, thanks to what Landry described as "the latent, 

very acute dust effect that's now inevitable."

There is hope. More snow — as in several feet piling deep and hiding the latest dust from penetrating sunshine — could delay the 

deluge.

Water managers across Colorado, many of whom fund Landry's research, lament the late-season dirt. That dark layer covering even 

the deepest snowpack prevents the slow and steady runoff that keeps rivers rolling and reservoirs replenished.

Instead, the runoff comes down at once, forcing precious water that could irrigate fields in July and float rafts in August to run 

through the state months early.

"Snowpack above 9,000 feet is our biggest water storage, and our best reservoir, and we want to keep water in that reservoir as long 

as possible," said Jim Pokrandt with the Colorado River Water Conservation District. "The worse these dust layers are, you get the 

snow (disappearing) quicker and that affects late-season base flows in streams. The effects are felt from high elevation down to 

where we use the water for irrigation."

Still, Pokrandt noted, at least "there is more snow to melt," especially in the Colorado River Basin, which saw its snow-waterequivalent climb from 72 percent of average in early February to 97 percent of average after Wednesday's storm.

http://www.denverpost.com/breakingnews/ci_23057359/good-news-deep-snow-colorado-foiled-by-dust?source=rss
66

Historical Weather For The Last Twelve Months in Telluride, Colorado, USA

Location

This report describes the historical weather record at the Telluride Regional Airport (Telluride, Colorado, United 

States) during the last 12 months. This station has records back to February 1987.

Telluride, Colorado has a humid continental climate with warm summers and no dry season. The area within 25 

miles of this station is covered by forests(98%)

(Excerpt:)

Wind

The highest sustained wind speed was 31 mph, occurring on August 17; the highest daily mean wind speed was 17 

mph (April 16); and the highest wind gust speed was 53 mph (April 16).

The windiest month was April, with an average wind speed of 7 mph. The least windy month wasAugust, with an 

average wind speed of 4 mph.

Wind Speed

The daily low and high wind speed (light gray area) and the maximum daily wind gust speed (tiny blue dashes).

http://weatherspark.com/history/31757/2013/Telluride-Colorado-United-States
67

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Station Fields: El Station Number El Station Name 

---,----.- -cC:-o-lo-ra_do _ ----.- LP - La Plata 

Staron Total I I Date .1. Nu~ber Station Name Comments --- m. 

4/17/2013 CO-LP-20 Durango 10 NNE 0.00 

4/17/2013 CO-LP-26 Hesperus 13.3 SSW 0.00 

4/17/2013 CO-LP-35 Bayfield 7.0 N T 

No moisture to report. With a high 

temperature of 68.9 deg F and a low of 

41.4 deg F overnight@ Station elevation of View 

6700 

Not a nice day windy, dusty visibility one 

mile at times 68°, 39° current 40° View 

Two days of dirty wind from NM and then a 

brief snow shower sideways! View 

4/17/2013 CO-LP-34 Durango 7.1 N 0.00 Very dusty 

4/16/2013 CO-LP-20 Durango 10 NNE 0.00 

4/16/2013 CO-LP-25 Bayfield 0.6 WSW 0.00 

4/16/2013 CO-LP-41 Durango 0.7 NNE 0.00 

4/16/2013 CO-LP-61 Durango 4.8 WSW 0.00 

No moisture to report. With a high 

temperature of 67.8 deg F and a low of 

41.2 deg F overnight@ Station elevation of View 

6700 

The air is filled with dust this morning, as it 

was almost all day yesterday. View 

signif. wind/dust event 

Visibility down to about 5 miles in dust and 

haze. 

4/16/2013 CO-LP-26 Hesperus 13.3 SSW 0.00 Windy, dusty 67°, 39° current 40° 

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Ill 

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74

5.0 Not Reasonably Controllable or Preventable: Local 

Particulate Matter Control Measures

While it is likely that some dust was generated within the local communities as gusts from the regional 

dust storm passed through the area, the amount of dust generated locally was easily overwhelmed by, and 

largely unnoticeable as compared to the dust transported in from the source regions of the dust storm. 

The following sections will describe in detail the regulations and programs in place designed to control 

PM10 in each affected community. These sections will demonstrate that the event was not reasonably 

controllable, as laid out in Section 50.1(j) of Title 40 CFR 50, within the context of reasonable local 

particulate matter control measures. 

The following subsections describe in detail applicable Best Available Control Measures (BACM), 

reasonable control measures, applicable federal, state, and local regulations, appropriate land use 

management, and an analysis of potential areas of local soil disturbance for Telluride during the April 16, 

2013 event. This information shall confirm that no unusual anthropogenic actions occurred in Telluride 

on April 16, 2013.

Regulatory Measures- State

The Division’s regulations on PM10 emissions are summarized in Table 13.

Table 13: State Regulations Regulating Particulate Matter Emissions.

Rule/Ordinance Description

Colorado Department of Public Health and 

Environment

Regulation 1- Emission Control For Particulate 

Matter, Smoke, Carbon Monoxide, And Sulfur 

Oxides

Regulates emissions of particulates, smoke, sulfur 

dioxide, and nitrogen oxides and establishes limits 

on these pollutants from covered sources.

Applicable sections include but are not limited to:

Everyone who manages a source or activity that is 

subject to controlling fugitive particulate emissions 

must employ such control measures and operating 

procedures through the use of all available practical 

methods which are technologically feasible and 

economically reasonable and which reduce, prevent 

and control emissions so as to facilitate the 

achievement of the maximum practical degree of 

air purity in every portion of the State. Section 

III.D.1.a)

Anyone clearing or leveling of land greater than 

five acres in attainment areas or one acre in nonattainment areas from which fugitive particulate

emissions will be emitted are required to use all 

available and practical methods which are 

technologically feasible and economically 

reasonable in order to minimize fugitive particulate 

emissions.(Section III.D.2.b)

Control measures or operational procedures for 
75

Rule/Ordinance Description

fugitive particulate emissions to be employed may 

include planting vegetation cover, providing 

synthetic cover, watering, chemical stabilization, 

furrows, compacting, minimizing disturbed area in 

the winter, wind breaks and other methods or 

techniques approved by the Division. (Section 

III.D.2.b)

Any owner or operator responsible for the 

construction or maintenance of any existing or new 

unpaved roadway which has vehicle traffic 

exceeding 200 vehicles per day in the 

attainment/maintenance area and surrounding areas 

must stabilize the roadway in order to minimize 

fugitive dust emissions (Section III.D.2.a.(i))

Colorado Department of Public Health and 

Environment

Regulation 3- Stationary Source Permitting and Air 

Pollutant Emission Notice Requirements 

Construction Permit required if a land development 

project exceeds 25 acres and spans longer than 6 

months in duration (Section II.D.1.j)

Colorado Department of Public Health and 

Environment

Regulation 4- New Wood Stoves and the Use of 

Certain Woodburning Appliances During High 

Pollution Days

Regulates wood stoves, conventional fireplaces and 

woodburning on high pollution days. 

Prohibits the sale and installation a wood-burning 

stove in Colorado unless it has been tested, 

certified, and labeled for emission performance in 

accordance with criteria and procedures specified 

in the Federal Regulations and meets emission 

standards. (Section II) 

Section III regulates pellet stoves. Section IV 

regulates masonry heaters. Section VII limits the 

use of stoves on high pollution days. 

Colorado Department of Public Health and 

Environment

Regulation 6- Standards of Performance for New 

Stationary Sources

Implements federal standards of performance for 

new stationary sources including ones that have 

particulate matter emissions. (Section I)

Colorado Department of Public Health and 

Environment

Regulation 9- Open Burning, Prescribed Fire, and 

Permitting

Prohibits open burning throughout the state unless 

a permit has been obtained from the appropriate air 

pollution control authority. In granting or denying 

any such permit, the authority will base its action 

on the potential contribution to air pollution in the 

area, climatic conditions on the day or days of such 

burning, and the authority’s satisfaction that there 

is no practical alternate method for the disposal of 

the material to be burned. Among other permit 

conditions, the authority granting the permit may 

impose conditions on wind speed at the time of the 

burn to minimize smoke impacts on smokesensitive areas. (Section III)

Colorado Department of Public Health and Applies to all emissions sources in Colorado
76

Rule/Ordinance Description

Environment- Common Provisions Regulation

When emissions generated from sources in 

Colorado cross the state boundary line, such 

emissions shall not cause the air quality standards 

of the receiving state to be exceeded, provided 

reciprocal action is taken by the receiving state. 

(Section II A)

Colorado Department of Public Health and 

Environment- Air Quality Standards, Designations 

and Emission Budgets

Telluride has a mobile source emissions budget of 

1,108 pounds-per-day for PM10 (Section V.A.4.J). 

The emissions budget establishes a cap on mobile 

source emissions and is administered though the 

transportation conformity regulations.

Colorado Department of Public Health and 

Environment- State Implementation Plan, Specific 

Regulations for NonattainmentAttainment/Maintenance Areas (Local Elements)

Section II- Documents the specific PM10 control 

strategies for Telluride and San Miguel County

Federal Motor Vehicle Emission Control Program The federal motor vehicle emission control 

program has reduced PM10 emissions through a 

continuing process of requiring diesel engine 

manufacturers to produce new vehicles that meet 

tighter and tighter emission standards. As older, 

higher emitting diesel vehicles are replaced with 

newer vehicles, the PM10 emissions in areas will be 

reduced.

Control Measures Included in the Attainment/Maintenance Plan

The Telluride area will rely on the control programs listed below to demonstrate maintenance of the 24-

hour PM10 standard through 2021. No emission reduction credit has been taken in the 

attainment/maintenance demonstration for any other current State or local control programs and no other 

such programs, strategies, or regulations shall be incorporated or deemed as enforceable measures for the 

purposes of this maintenance demonstration.

The attainment/maintenance plan takes credit for the following federally-enforceable control measures, 

which, except where otherwise noted, are included in the SIP:

Federal fuels and tailpipe standards and regulations

Current federal regulations concerning motor vehicles, fuels, small engines, diesels, and non-road 

mobile sources. While credit is taken for these federal requirements, they are not part of the 

Colorado SIP. 

Woodburning

The Town of Telluride and San Miguel County have adopted wood and coal burning emission 

reduction measures in addition to the requirements of Air Quality Control Commission 

Regulation 4 (approved by EPA as part of the federal SIP in 1997), referenced in Table 13. These 

wood and coal burning controls were adopted and implemented throughout the 1980s and early 

1990s, were approved by EPA in 1994, and are defined in detail in Section II. A of the “State
77

Implementation Plan-Specific Regulations for Nonattainment – Attainment/Maintenance Areas” 

(Local Elements) referenced in Table 13. 

Stationary Sources

Emissions from stationary sources of pollution are regulated by several Air Quality Control 

Commission Regulations. These regulations (No. 1, No. 3, No. 6, and The Common Provisions) 

are referenced in Table 13.

As an attainment/maintenance area since August 14, 2001, the State and federal attainment PSD 

permitting requirements remain in effect in the Telluride area. This program requires the 

application of Best Available Control Technology when constructing new or modified major 

stationary sources.

Street Sanding Controls

The Town of Telluride has a town-wide street sweeping program that provides for town streets to 

be swept approximately two hundred and thirty days a year. This effort removes between 750 and 

1200 cubic yards of sediment from the streets each year, greatly improving the air quality. The 

town utilizes two Tennant Company mechanical sweepers. There is a requirement that any user 

that applies street sanding material in the Telluride attainment/maintenance area must use 

materials containing less than two percent fines. This strategy was adopted in 1994 and approved 

by EPA in 1996, and it is defined in detail in Section II.B. of the “State Implementation PlanSpecific Regulations for Nonattainment –Attainment/Maintenance Areas (Local Elements) 

referenced in Table 13.

Construction Mitigation Plan 

Article 11 of Telluride’s Municipal Code houses the town’s Construction Mitigation Plan (CMP). 

The purpose of the CMP is to reduce air and other pollution caused by dust, dirt, silt, trash, 

construction debris and other materials that could migrate from a construction site. The CMP 

also requires the revegetation of sites used in the construction process which are not otherwise 

revegetated as part of the construction project.

Windblown Dust from Disturbed Soils

Examination of available satellite imagery in Telluride has shown very limited construction and soil 

disturbance within the village since 2003, particularly south of the PM10 monitor. The monitor is only 2 

blocks north from the base of the ski resort, and available land south of the monitor is essentially built 

out. One 1.4 acre project was constructed approximately 1⁄2 mile WSW of the monitor sometime between 

June 2005 and August 2011. As construction to the south of the monitor was finished before 2011, any 

construction activities are unlikely to have played a role in the April 2013 exceedance.
78

Figure 45: June 2005 and August 2011 Google Earth views of Telluride Village, with one project of 1.4 

acre new construction.

Monitor

Monitor

June 2005

August 2011, 

1.4 acres

New 1600 

square 

foot house
79

6.0 Summary and Conclusions

APCD is requesting concurrence on exclusion of the 265 μg/m3 PM10 value from Telluride (08-113-

0004) on April 16, 2013. (APCD will request concurrence on exclusion of other PM10 values taken 

on the same day at a later date.)

On April 16, 2013, a powerful spring storm system caused multiple exceedances of the twenty-four hour 

PM10 NAAQS in west-central and southwest Colorado. These PM10 sample values include Telluride (265

μg/m3), Durango (419 μg/m3), Pagosa Springs (295 μg/m3), Alamosa Adams State College (237 μg/m3), 

and Mt. Crested Butte (187 μg/m3).

The statistical and meteorological data clearly shows that but for this high wind blowing dust event, 

Telluride would not have exceeded the 24-hour NAAQS on April 16, 2013. The PM10 exceedances on 

April 16, 2013, would not have occurred if not for the following: (a) dry soil conditions over southeastern 

Utah, northeastern Arizona, and portions of extreme northwestern New Mexico; (b) a combination of 

strong surface low pressure and a cold front associated with an intense upper-level trough that was 

moving across the western United States that created conditions necessary for widespread strong gusty 

winds over the area of concern; and (c) elevated friction velocities and the deep mixing of the blowing 

dust from desert regions of Arizona, northwest New Mexico, and southeast Utah.

Surface weather maps for the Four Corner States show evidence of widespread blowing dust and winds 

above the threshold speeds for blowing dust on April 16, 2013. This surface analysis shows that winds 

were as high as 50 mph and wind gusts were as high as 66 mph. These speeds are above the thresholds 

for blowing dust identified in EPA draft guidance and in detailed analyses completed by the State of 

Colorado. These PM10 exceedances were due to an exceptional event associated with regional windstormcaused emissions from erodible soil sources over a large area of southeastern Utah, northeastern Arizona, 

and portions of extreme northwestern New Mexico. These sources are not reasonably controllable during 

a significant windstorm under abnormally dry or moderate drought conditions.

The blowing dust climatology for the Four Corners area indicates that the area can be susceptible to 

blowing dust when winds are high. Landform imagery shows that northeastern Arizona and southeastern 

Utah in particular have experienced a long-term pattern of wind erosion and blowing dust when winds 

have been southwesterly and blowing into western and southern Colorado. Forecast products from the 

Navy Aerosol Analysis and Prediction System model provide evidence for a widespread blowing dust 

event in the Four Corners states, suggesting that significant source regions for dust transported into 

Colorado were located in arid regions of Arizona, Utah, and New Mexico. NOAA HYSPLIT forward and 

backward trajectories provide clear supporting evidence that dust from desert regions of northwest New 

Mexico and Arizona caused the PM10 exceedances measured across portions of southwest Colorado on 

April 16, 2013. Soils in the Four Corners area and in northeast Arizona and extreme northwestern New 

Mexico in particular were dry enough to produce blowing dust when winds were above the thresholds for 

blowing dust.

Both wind speeds and soil moisture in the Four Corners area and northeastern Arizona were conducive to 

the generation of significant blowing dust. Multiple sources of data for the event in question and analyses 

of past dust storms in this area prove that this was a natural event and, more specifically, a significant 

natural dust storm originating in northeastern Arizona and northwestern New Mexico and spreading into 

southwestern Colorado. 
80

Friction velocities in a wide area of northeast Arizona, northwest New Mexico, southeast Utah, and 

southwest Colorado were above 1.0 meters per second on April 16, 2013. Even undisturbed desert soils 

normally resistant to wind erosion will be susceptible to blowing dust when friction velocities are greater 

than about 1.0 to 2.0 meters per second. Note that blowing dust will typically only occur where these 

values are high and the soils are dry and not protected by vegetation, forest cover, boulders, rocks, etc. 

This is why blowing dust occurred in the desert and more arid areas of northern Arizona, northwestern 

New Mexico, southeastern Utah, and southwestern Colorado on April 16, 2013. The elevated friction 

velocities, the data on soil moisture conditions, and the prevalence of winds above blowing dust 

thresholds (all occurring in traditional source regions in northeastern Arizona and northwestern New 

Mexico) prove that this dust storm was a natural event that was not reasonably controllable or 

preventable. 

MODIS Terra satellite image shows that the Four Corners region including Utah, Arizona, New Mexico, 

and Colorado were sources regions for blowing dust on April 16, 2013. This is consistent with the 

climatology for many dust storms in Colorado as described in the Grand Junction, Colorado, Blowing 

Dust Climatology report contained in Appendix A of this document. The observations of winds above 

blowing dust thresholds and restricted visibilities in the areas of concern demonstrate that this is a natural 

event that cannot be reasonably controlled or prevented. 

The Center for Snow and Avalanche Studies has been studying the effects of wind-blown desert dust from 

Arizona, New Mexico, and Utah on snowpack albedo and snowmelt in the San Juan Mountains of 

Colorado. The Center for Snow and Avalanche Studies lists April 16, 2013, as a Dust-on-Snow event for 

the 2012/2013 water year, and this provides clear supporting evidence that a regional blowing dust event 

with long-range transport caused the PM10 exceedances measured across portions of Colorado on April 

13, 2013. In addition, the snow depth analysis illustrates that the mountains surrounding Telluride had 16

to 100 inches of snow cover in the hours before the dust storm of April 16, 2013. These data provide 

strong evidence that a widespread, regional, blowing dust event caused exceedances at these locations

rather than local sources.

But for the dust storm on April 16, 2013, this exceedance at Telluride (08-113-0004) would not have 

occurred. 
81

7.0 References

Draxler, R.R. and Rolph, G.D., 2012. HYSPLIT (HYbrid Single-Particle Lagrangian Integrated 

Trajectory) Model access via NOAA ARL READY Website (http://ready.arl.noaa.gov/HYSPLIT.php). 

NOAA Air Resources Laboratory, Silver Spring, MD. 

Marticorena, B., G. Bergametti, D. Gillette, and J. Belnap, 1997, Factors controlling threshold friction 

velocity in semiarid and arid areas of the United States, Journal of Geophysical Research 102 D19, 

23,277-23, 287. 

Technical Services Program, Air Pollution Control Division, Colorado Department of Public Health and 

Environment, November 22, 2011, Technical Support Document for the January 19, 2009 Lamar 

Exceptional Event. 

United States Environmental Protection Agency, June 2012, Draft Guidance on the Preparation of 

Demonstrations in Support of Requests to Exclude Ambient Air Quality Data Affected by High Winds 

under the Exceptional Events Rule.
A-1

Appendix A- Grand Junction, Colorado, Blowing Dust Climatology 

January 24, 2012

There can be significant transport of regional blowing dust into Grand Junction from source regions in 

Utah and Arizona. While there are sources for wind-blown dust within the Grand Valley and Grand 

Junction itself, there is evidence from the analysis of soil features, wind and precipitation climatology, 

and statistical analyses of Grand Junction exceedances of the PM10 standard that regional sources often 

play a significant role during these blowing dust events. This document provides a weight of evidence 

analysis for dust transport into Colorado.

Grand Junction, Colorado, is located in a part of the country that is largely arid to semi-arid. Figure A-1 

through A-3 show the annual average precipitation for Colorado, Arizona, and Utah, respectively. Grand 

Junction is in the Grand Valley of Western Colorado where the annual precipitation is typically less than 

10 inches. Northeastern Arizona, which is frequently upwind of Grand Junction during blowing dust 

events, receives between 5 and 15 inches of precipitation each year. The Colorado River Basin in eastern 

and southeastern Utah, which is also frequently upwind of Grand Junction during blowing dust events, 

also receives 5 to 10 inches per year.

Figure A-4 shows the 1971-2000 monthly normal precipitation amounts for Grand Junction, Colorado. 

The annual average for this time period is 8.99 inches. The wettest months are March through May and 

August through October. The driest months are January, February, June, July, November, and December. 

These months receive an average of 0.57 inches per month. The annual monthly average precipitation is 

0.75 inches.

Arid to semi-arid soils make much of the region susceptible to blowing dust. The map in Figure A-5 

shows that portion of the Colorado Plateau (circled in red) where modern wind erosion features are 

common and clearly visible in Google Earth images. These features include longitudinal dunes and other 

sand or soil erosion structures with a predominant southwest to northeast orientation. This orientation is 

the result of the predominant southwesterly flow that occurs during high wind and blowing dust events in

the region. Figures A-6 through A-12 present aerial views of ubiquitous erosion features in northeastern 

Arizona and southeastern Utah. The Painted Desert of northeastern Arizona is frequently the source for 

much of the blowing dust in the Four Corners region. Figure A-13 provides a particularly good satellite 

image of a blowing dust event originating in the Painted Desert and extending northeastward across the 

junction of the Four Corners (source: NASA Tera satellite, http://earthobservatory.nasa.gov/IOTD/view.php?id=37791). 

Strong southwesterly winds caused this blowing dust event.

The text that accompanies this image on NASA’s Earth Observatory 10th Anniversary page follows 

below:

“A dust storm struck northeastern Arizona on April 3, 2009. With winds over 145 kilometers (90 

miles) per hour reported near Meteor Crater, east of Flagstaff, the storm reduced visibility and 

forced the temporary closure of part of Interstate 40, according to The Arizona Republic.

The Moderate Resolution Imaging Spectroradiometer (MODIS) on NASA’s Terra satellite 

captured this image on April 3, 2009. Clear skies allow a view of multiple source points of this 

dust storm. The source points occur along an arc that runs from northwest to southeast.

This dust storm occurred in the area known as Arizona’s Painted Desert, and the dust plumes 

show why. Whereas many dust plumes are uniform in color, these plumes resemble a band of 
A-2

multicolored ribbons, ranging from pale beige to red-brown, reflecting the varied soils from 

which the plumes arise. The landscapes of the Painted Desert are comprised mostly of Chinle 

Formation rocks—remains of sediments laid down during the time of the first dinosaurs, over 200 

million years ago.”
A-3

Figure A-1. Average annual precipitation in Colorado based on 1961-1990 normals.
A-4

Figure A-2. Average annual precipitation in Arizona based on 1961-1990 normals.
A-5

Figure A-3. Average annual precipitation in Utah based on 1961-1990 normals.
A-6

Figure A-4. 1971-2000 monthly normal precipitation in Grand Junction Colorado. 

Figure A-5. The portion of the Colorado Plateau in Utah, Arizona, and New Mexico that exhibits 

widespread surface soil and sand erosion features in Google Earth imagery. Much of the highlighted area 

within Arizona is within the Painted Desert.

0.00

0.25

0.50

0.75

1.00

1.25

1.50

1 2 3 4 5 6 7 8 9 10 11 12

Precipitation - Inches

Month

Grand Junction 1971-2000
A-7

Figure A-6. Southwest to northeast soil and sand erosion structures in southeastern Utah.

Figure A-7. Southwest to northeast soil and sand erosion structures in northeastern Arizona (Painted 

Desert).
A-8

Figure A-8. Southwest to northeast soil and sand erosion structures in southeastern Utah.

Figure A-9. Southwest to northeast soil and sand erosion structures in northeastern Arizona (Painted 

Desert). The slip faces of dunes (lighter bands) face in the direction of wind flow – toward the northeast.
A-9

Figure A-10. Southwest to northeast soil and sand erosion structures in southeastern Utah.

Figure A-11. Southwest to northeast soil and sand erosion structures in northeastern Arizona (Painted 

Desert). 
A-10

Figure A-12. Southwest to northeast soil and sand erosion structures in northeastern Arizona (Painted 

Desert).
A-11

Figure A-13. NASA Tera satellite image of a dust storm on April 3, 2009, in southwesterly flow over the 

Painted Desert of northeastern Arizona (http://earthobservatory.nasa.gov/IOTD/view.php?id=37791). 
A-12

Figure A-14 displays the surface weather map for this event (00Z April 4, 2009, or 5 PM MST April 3, 

2009). A strong low pressure system in southern Colorado, strong southwesterly winds in the Four 

Corners area, and the blowing dust symbol (infinity sign) at Farmington (New Mexico) and Cortez 

(Colorado) are evident in this map. Blowing dust in this region is frequently associated with 

southwesterly flow.

Figure A-14. Surface weather map for 00Z April 4, 2009, (5 PM MST April 3, 2009), showing a strong

low pressure system in southern Colorado, strong southwesterly winds in the Four Corners area and the 

blowing dust symbol (infinity sign) at Farmington (New Mexico) and Cortez (Colorado).

A USGS map of the Colorado Plateau in Figure A-15 shows the prevalence of eolian or wind-blown sand 

deposits in southeastern Utah and northeastern Arizona. An analysis of the annual frequency of dust 

storms (Orgill and Sehmel, 1976) in the western half of the U.S. suggests that portions of eastern and 

western Utah and northeastern Arizona are source regions for blowing dust (see Figure A-16). Soil and 

sand structures point to the prevalence of southwesterly flow during blowing dust events, and 

precipitation climatology highlights the potential for blowing dust across much of the region. In 

addition, an analysis of back trajectories associated with high PM10 concentration events in Grand 

Junction discussed in the next section of this document supports the conclusion that soils in Arizona and 

Utah are likely significant contributors to PM10 measured during many dust storms affecting Grand 

Junction.
A-13

Figure A-15. USGS map of eolian sand features on the Colorado Plateau 

(http://geochange.er.usgs.gov/sw/impacts/geology/sand/ ).

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A-14

Figure A-16. Number of dust storms per year from: Orgill, M.M., Sehmel, G.A., 1976. Frequency and 

diurnal variation of dust storms in the contiguous USA. Atmospheric Environment 10, 813–825.

NOAA HYSPLIT 36-hour back trajectories were calculated for Grand Junction for the eight 24-hour 

periods from 2004 through early 2009 with the Powell monitor PM10 concentrations in excess of 75 

μg/m3, strong regional winds, and dry soils. Trajectories were modeled every 4 hours for each day. Data 

presented later in this document provides evidence that the moderate to high PM10 levels on these days 

were from blowing dust. The 6 back trajectories for each day were calculated for an arrival height of 500 

meters using EDAS40 data and model vertical velocities (see: http://www.arl.noaa.gov/HYSPLIT.php ). 

The eight days used in the analysis and the Powell monitor concentrations measured on these days are 

presented in Table A-1. 
A-15

The back trajectories for these high-concentration days are shown in Figure A-17. Transport was 

generally from the west through southwest. A high density of trajectory points is found in northeast 

Arizona and southeast Utah. Most of these trajectories in Figure A-17 are also consistent with transport 

from or across suspected or known blowing dust source regions highlighted in Figures A-5, A-13, A-15, 

and A-16.

Table A-1. Grand Junction Powell monitor days with concentrations in excess of 75 c and blowing dust 

conditions (from 2004 through early 2009).

Year Month Day

Powell 24-hour PM10 concentration 

in c

2005 4 19 197.8

2008 4 15 116.1

2008 4 21 103.6

2004 9 3 102

2006 3 3 98.3

2008 5 21 86.7

2008 4 30 83.5

2006 6 7 77.9
A-16

Figure A-17. NOAA HYSPLIT 36-hour back trajectories for Grand Junction for those eight 24-hour periods from 

2004 through early 2009 with the Powell monitor PM10 concentrations in excess of 75 c, strong regional winds, 

and dry soils. Trajectory points are sized and color-coded to reflect 24-hour PM10 concentrations in c. 

Trajectories were calculated every 4 hours for each day. 

The trajectories in Figure A-17 point to the possibility that, at times, dust from Utah and Arizona can have a 

major impact on Grand Junction and less of an impact elsewhere in western Colorado. This non-homogeneity is 

possible given the fact that dust storms are frequently organized into discreet plumes from discreet areas that 

maintain their integrity for long distances. An example of this can be seen in Figure A-18 that shows plumes of 

dust in New Mexico during a windstorm on May 20, 2008.

Figure A-19 shows the NOAA HYSPLIT back trajectories for the highest concentration day during the 2004 

through early 2009 period: April 19, 2005. Twenty-four hour back trajectories for each hour during the period 

with high winds (using EDAS40 data and 500-meter arrival heights) show that the back trajectories for Grand 

Junction were more likely to have crossed the Painted Desert and southeastern Utah than those for Telluride and 

Durango, which measured lower PM10 concentrations on this day.

Figure A-18. Discreet plumes of blowing dust in New Mexico, Mexico, and Arizona visible in GOES satellite 

imagery for May 20, 2008 (http://www.osei.noaa.gov/Events/Dust/US_Southwest/2008/DSTusmx142_G12.jpg ).

K-means cluster analysis has been applied to Grand Junction Powell PM10 concentrations, Grand Junction and 
A-17

Painted Desert 30-day total precipitation for each PM10 monitoring day, and Grand Junction and Painted Desert 

daily maximum wind gust speeds for each monitoring day. K-means cluster analysis is a statistical method for 

identifying clusters or groupings of values for many variables. For environmental variables, these clusters often 

represent distinct processes, conditions, or events. In this case, cluster analysis differentiates PM10 concentrations 

associated with strong winds, low soil moistures, and blowing dust by providing mean values for these 5 variables 

for 5 distinct categories of PM10 events. The period of record considered was from January 2004 through March 

2009. The Hopi weather station located in the central portion of the Painted Desert was used to represent Painted 

Desert conditions in northeastern Arizona, and the Grand Junction National Weather Service station was used to 

represent Grand Junction conditions. The 30-day total precipitation values appear to be a better metric for 

blowing dust conditions than shorter-term totals.

Figure A-19. 24-hour NOAA HYSPLIT back trajectories for every hour from 1500 MST to 2200 MST for Grand 

Junction (red), Telluride (green), and Durango (blue) for the dust storm of April 19, 2005.

The results of the cluster analysis are presented in Table A-2 below. Cluster 1 represents high soil moisture 

conditions, moderate gust speeds, and low PM10 concentrations. Cluster 2 represents very low soil moisture, 

moderate PM10, and low gust speeds. Cluster 3 represents low soil moisture, moderate gusts, and low PM10. 

Cluster 4 represents moderate soil moisture, low gusts, and low PM10. Finally, Cluster 5 represents high PM10, 

high gusts, and low soil moisture. Cluster numbers, Grand Junction Powell PM10 concentrations, and Grand 

Junction daily maximum gust speeds are plotted in Figure A-20.
A-18

The data in Figure A-20 clearly show that the highest PM10 concentrations tend to occur in Cluster 5 with gusts 

above 40 mph. The only exceedance in this period occurred on a day with a peak gust of 43 mph. Cluster 2 is 

likely to be indicative of wintertime inversion conditions with lighter winds and moderately elevated PM10. 

Figure A-21 shows the concentrations and cluster values associated with Hopi station daily maximum gust 

speeds. The overall pattern is similar. The highest concentration day is associated with a peak gust of 47 mph at 

Hopi. All of the days/events presented in Figure A-17, A-19, and Table A-1 were classified as Cluster 5.

Table A-2. K-means cluster analysis means for Grand Junction PM10 and meteorological variables.

Cluster Variables

Cluster 1 

Means

Cluster 2 

Means

Cluster 3

Means

Cluster 4

Means

Cluster 5

Means

Powell 24-hour PM10 in c 24.5 37.3 24.3 21.8 74.9

Hopi Wind Gust in mph 20.8 18.0 32.5 20.7 40.5

Grand Junction Wind Gust in mph 20.4 16.5 31.8 19.6 43.1

Grand Junction 30-day 

Precipitation 1.7 0.4 0.5 0.8 0.6

Hopi 30-day Precipitation 1.8 0.2 0.5 0.7 0.3

Count 85 120 170 147 24

Figure A-20. Grand Junction Powell 24-hour PM10 concentrations versus Grand Junction gust speed by 

cluster.

Figures A-22 and A-23 show Powell PM10 concentrations versus Grand Junction and Hopi 30-day 

precipitation totals, respectively, by cluster. The blowing dust group, Cluster 5, is generally associated 

0

50

100

150

200

250

051 01 52 02 53 03 54 04 55 05 56 0

Grand Junction Gust Speed in mph

Grand Junction Powell 24-hr PM10 - ug/m3

Clusters

1

4

2

3

5
A-19

with 30-day precipitation totals of less than 1.00 inches at Grand Junction and less than 0.50 inches at 

Hopi. While this is not proof that the measured dust in Grand Junction is from Arizona, it adds to the 

weight of evidence that the Painted Desert makes a significant contribution to PM10 concentrations in 

Grand Junction during many blowing dust events. Of interest in this regard are the two high 

concentrations (greater than 100 c) that occurred when Grand Junction 30-day precipitation totals were 

greater than an inch (see Figure A-22). One of these occurred when transport was from the southwest. 

On this day (April 21, 2008) the NOAA Satellite Smoke Text Archive reported the following (see 

http://www.ssd.noaa.gov/PS/FIRE/smoke.html ):

“Blowing dust is seen over most of Utah (and part of western Nevada) and the dust is moving toward the 

northeast, reaching into northwestern Colorado and southern Wyoming.”

Figure A-21. Grand Junction Powell 24-hour PM10 concentrations versus Hopi gust speed by cluster.

0

50

100

150

200

250

051 01 52 02 53 03 54 04 55 05 56 0

Hopi Gust Speed in mph

Grand Junction Powell 24-hr PM10 - ug/m3

Clusters

3

4

5

1

2
A-20

Figure A-22. Grand Junction Powell 24-hour PM10 concentrations versus Grand Junction 30-day total 

precipitation by cluster.

Figure A-23. Grand Junction Powell 24-hour PM10 concentrations versus Hopi 30-day total precipitation 

by cluster.

0

50

100

150

200

250

0.0000.2500.5000.7501.0001.2501.5001.7502.0002.2502.5002.7503.000

Grand Junction 30-day Precipitation in Inches

Grand Junction Powell 24-hr PM10 - ug/m3

Clusters

4

2

3

1

5

0

50

100

150

200

250

0.0000.2500.5000.7501.0001.2501.5001.7502.0002.2502.5002.7503.000

Hopi 30-day Precipitation in Inches

Grand Junction Powell 24-hr PM10 - ug/m3

Clusters

3

4

5

1

2
A-21

The other occurred on April 15, 2008, when the flow was from Arizona and southeast Utah. The transport 

conditions, the discrepancy between high recent precipitation in Grand Junction and low recent precipitation at 

Hopi for these two days, and, in one case, analyst discussion of what was visible in satellite images suggest that 

much of the dust might have originated from outside of the Grand Junction environment. 

Figure A-24 shows Grand Junction Powell 24-hour PM10 concentrations versus peak gust wind directions at the 

Little Delores RAWS weather station about 25 miles west-southwest of Grand Junction. Grand Junction is 

situated on the floor of the Grand Valley, a major northwest to southeast trending basin than can force or channel 

synoptic scale flows. As a result, surface wind directions in Grand Junction may not be useful indicators of the 

direction of longer-range transport. Little Delores is on the Umcompahgre Plateau, and winds here are more 

likely to reflect the larger-scale transport directions for the region. This graph indicates that high PM10 at Grand 

Junction (Cluster 5) is associated with winds from the south-southeast to west-southwest at Little Delores. These 

directions point to dust sources in southeast Utah and northeastern Arizona. This is further evidence that dust 

from these areas may make a significant contribution to PM10 measured in Grand Junction during blowing dust 

events.

Figure A-24. Grand Junction Powell 24-hour PM10 concentrations versus peak gust wind directions at the Little 

Delores RAWS weather station, by cluster.

Figure A-25 presents monthly percentiles for Grand Junction gust speeds. Wind gusts generally considered to be 

high enough for significant blowing dusts (40 mph or higher) are within the upper 5 to 15 percent during each 

month of the year. Consequently, these events can be viewed as exceptional rather than normal. Gusts in this 

category can occur any month of the year, but are most likely in March, April, May and October. Figure A-4 

shows that in Grand Junction these are typically among the wettest months of the year. It is in drier years, 

therefore, that blowing dust may be most prevalent during the spring and fall months. January, February, and 

0

50

100

150

200

250

03 06 09 0120150180210240270300330360

Little Delores Gust Direction

Grand Junction Powell 24-hr PM10 - ug/m3

Clusters

1

4

2

3

5
A-22

June are typically very dry, and might be expected to have a significant proportion of blowing dust events.

Figures A-26 and A-27 show histograms for Grand Junction and Hopi wind gusts, respectively. The 95th

percentile gust speed for Grand Junction is 43 mph. For Hopi it is 41 mph. For both sites, it is clear that gusts in 

the range that is associated with blowing dust are the exception rather than the rule. Cluster analysis also shows 

that the blowing dust events represent only 4% of the PM10 sample days (from Table A-2, Cluster 5 had 24 cases 

out of a total of 546). The weight of evidence presented in this document clearly suggests that source regions in 

Arizona and Utah can have a significant impact on PM10 concentrations in Grand Junction during blowing dust 

events and that these events occur when dry soils are affected by winds of exceptional strength. Control of these 

sources, which are outside of Colorado, may not be reasonably achievable or possible.

The precipitation climatology for the Four Corners area indicates that the area can be susceptible to blowing 

dust when winds are high. Landform imagery shows that northeastern Arizona and southeastern Utah in 

particular have experienced a long-term pattern of wind erosion and blowing dust when winds have been 

southwesterly and blowing into western and southern Colorado. Back trajectories, case studies, satellite 

imagery, and statistical analyses have also shown that northeastern Arizona and southeastern Utah are a 

significant source for blowing dust transported into Colorado. Elevated PM10 in Grand Junction during 

windstorms is generally associated with wind gusts of 40 mph or higher at Grand Junction and Hopi in 

northeastern Arizona and southwesterly flow in Grand Junction. Elevated PM10 in Grand Junction is generally 

associated with 30-day precipitation totals of less than 1.00 inches at Grand Junction and less than 0.50 inches at Hopi.

Reference:

Orgill, M.M., Sehmel, G.A., 1976. Frequency and diurnal variation of dust storms in the contiguous USA. 

Atmospheric Environment 10, 813–825

Figure A-25. Percentile plot of Grand Junction daily maximum 5-second gust speed in miles per hour 

showing that gusts of 40 mph or greater always occur within the top 15 percentile speeds for each month 

of the year.

0

10

20

30

40

50

60

70

1 2 3 4 5 6 7 8 9 10 11 12

Percentile Plot

Grand Junction Daily Max 5-second Gust in mph

Month

Gust Speed in mph

Top 15% in Red, Lower 15% in Blue, Median Orange

January 2004-February 2009
A-23

Figure A-26. Histogram of daily maximum 5-second wind gusts at Grand Junction based on January 2004 –

February 2009.

Figure A-27. Histogram of daily maximum 5-second wind gusts at Hopi based on January 2004 – February 2009.

0

71

143

214

286

357

429

500

0 10 20 30 40 50 60 70

Daily Max 5-second Gust in mph

Count

0

43

86

129

171

214

257

300

0 10 20 30 40 50 60 70

Daily Max Gust in mph

Count
B-1

Appendix B - Weather Warnings and Blowing Dust Advisories for 

April 16, 2013

693 

WWUS75 KGJT 161020

NPWGJT

URGENT - WEATHER MESSAGE

NATIONAL WEATHER SERVICE GRAND JUNCTION CO

420 AM MDT TUE APR 16 2013

COZ021-022-UTZ022-161830-

/O.NEW.KGJT.WI.Y.0005.130416T1900Z-130417T0200Z/

FOUR CORNERS/UPPER DOLORES RIVER-ANIMAS RIVER BASINSOUTHEAST UTAHINCLUDING THE CITIES OF...CORTEZ...DOVE CREEK...MANCOS...

DURANGO...BAYFIELD...IGNACIO...BLANDING...BLUFF...MEXICAN HAT

420 AM MDT TUE APR 16 2013

...WIND ADVISORY IN EFFECT FROM 1 PM THIS AFTERNOON TO 8 PM MDT

THIS EVENING...

THE NATIONAL WEATHER SERVICE IN GRAND JUNCTION HAS ISSUED A WIND

ADVISORY...WHICH IS IN EFFECT FROM 1 PM THIS AFTERNOON TO 8 PM

MDT THIS EVENING. 

* TIMING...STRONG WINDS WILL DEVELOP EARLY THIS AFTERNOON AND

 CONTINUE INTO THE EARLY EVENING.

* WINDS...SOUTHWEST 20 TO 30 MPH WITH GUSTS TO 50 MPH.

* VISIBILITY...BLOWING DUST WILL LIMIT VISIBILITY.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

A WIND ADVISORY MEANS THAT A SIGNIFICANT WIND EVENT IS EXPECTED

OR OCCURRING. WINDS THIS STRONG CAN MAKE DRIVING DIFFICULT. USE

EXTRA CAUTION. 

PEOPLE...ESPECIALLY THOSE WITH RESPIRATORY ILLNESSES... HEART

DISEASE...THE ELDERLY...AND CHILDREN ARE RECOMMENDED TO STAY

INDOORS AND AVOID PROLONGED OUTDOOR EXERCISE OR HEAVY EXERTION

DUE TO WIND-BLOWN DUST.

&&

$$

817 

WWUS75 KFGZ 161454

NPWFGZ
B-2

URGENT - WEATHER MESSAGE

NATIONAL WEATHER SERVICE FLAGSTAFF AZ

754 AM MST TUE APR 16 2013

...VERY WINDY CONDITIONS TODAY THROUGH TUESDAY...

A SPRING STORM SYSTEM WILL BRING STRONG SOUTHWEST WINDS TO MUCH

OF NORTHERN ARIZONA TODAY. THE STRONGEST WINDS ARE EXPECTED

ACROSS THE LITTLE COLORADO RIVER VALLEY...THE NORTHERN SLOPES OF

THE WHITE MOUNTAINS AND PORTIONS OF THE MOGOLLON RIM. AREAS OF

BLOWING DUST WILL LIKELY AFFECT TRAVEL ACROSS MUCH OF NORTHEAST

ARIZONA...INCLUDING INTERSTATE 40...HIGHWAYS 87...364...AND 191.

AZZ013-014-016-017-162300-

/O.EXP.KFGZ.WI.Y.0004.000000T0000Z-130416T1500Z/

/O.CON.KFGZ.HW.W.0002.130416T1500Z-130417T0200Z/

LITTLE COLORADO RIVER VALLEY IN NAVAJO COUNTYLITTLE COLORADO RIVER VALLEY IN APACHE COUNTYEASTERN MOGOLLON RIM-WHITE MOUNTAINSINCLUDING THE CITIES OF...WINSLOW...HOLBROOK...SNOWFLAKE...

ST. JOHNS...SPRINGERVILLE...SHOW LOW

754 AM MST TUE APR 16 2013

...HIGH WIND WARNING REMAINS IN EFFECT UNTIL 7 PM MST THIS

EVENING...

...WIND ADVISORY HAS BEEN UPGRADED TO A WARNING...

* TIMING...WINDS WILL RAPIDLY STRENGTHEN THROUGH THE MORNING 

 HOURS. 

* WINDS...SOUTHWEST 25 TO 35 MPH WITH GUSTS 45 TO 55 MPH EARLY...

 INCREASING TO 30 TO 40 MPH WITH GUSTS OF 55 TO 65 MPH. 

* IMPACTS...WINDS THIS STRONG CAN MAKE DRIVING DIFFICULT... 

 ESPECIALLY FOR HIGH PROFILE VEHICLES. MINOR PROPERTY DAMAGE 

 AND SPOTTY POWER OUTAGES ARE POSSIBLE WITH THE STRONGEST 

 GUSTS. AREAS OF DENSE BLOWING DUST ARE POSSIBLE ACROSS THE 

 LITTLE COLORADO RIVER VALLEY...AFFECTING TRAVEL ALONG 

 INTERSTATE 40. 

PRECAUTIONARY/PREPAREDNESS ACTIONS...

A WIND ADVISORY MEANS THAT SUSTAINED WINDS OF 30 TO 39 MPH...OR

GUSTS FROM 40 TO 57 MPH...ARE EXPECTED. WINDS THIS STRONG CAN

MAKE DRIVING DIFFICULT...ESPECIALLY FOR HIGH PROFILE VEHICLES.

CONSIDER SECURING LOOSE BELONGINGS ON YOUR PROPERTY.

A HIGH WIND WARNING MEANS A HAZARDOUS HIGH WIND EVENT IS EXPECTED

OR OCCURRING...WITH SUSTAINED WIND SPEEDS GREATER THAN 40 MPH OR

GUSTS GREATER THAN 58 MPH. WINDS THIS STRONG CAN CAUSE PROPERTY

DAMAGE. CONTINUE TO MONITOR THE LATEST FORECASTS. ADDITIONAL

WEATHER INFORMATION IS ON THE WEB AT WWW.WEATHER.GOV/FLAGSTAFF.

&&

$$
B-3

AZZ012-015-162300-

/O.CON.KFGZ.HW.W.0002.000000T0000Z-130417T0200Z/

LITTLE COLORADO RIVER VALLEY IN COCONINO COUNTYWESTERN MOGOLLON RIMINCLUDING THE CITY OF...FLAGSTAFF

754 AM MST TUE APR 16 2013

...HIGH WIND WARNING REMAINS IN EFFECT UNTIL 7 PM MST THIS

EVENING...

* WINDS...SOUTHWEST 25 TO 35 MPH WITH GUSTS 45 TO 55 MPH... 

 INCREASING TO 30 TO 40 MPH WITH GUSTS OF 55 TO 65 MPH. 

* IMPACTS...WINDS THIS STRONG CAN MAKE DRIVING DIFFICULT... 

 ESPECIALLY FOR HIGH PROFILE VEHICLES. MINOR PROPERTY DAMAGE 

 AND SPOTTY POWER OUTAGES ARE POSSIBLE WITH THE STRONGEST 

 GUSTS. AREAS OF DENSE BLOWING DUST ARE POSSIBLE ACROSS THE 

 LITTLE COLORADO RIVER VALLEY...AFFECTING TRAVEL ALONG 

 INTERSTATE 40. 

PRECAUTIONARY/PREPAREDNESS ACTIONS...

A HIGH WIND WARNING MEANS A HAZARDOUS HIGH WIND EVENT IS EXPECTED

OR OCCURRING...WITH SUSTAINED WIND SPEEDS GREATER THAN 40 MPH OR

GUSTS GREATER THAN 58 MPH. WINDS THIS STRONG CAN CAUSE PROPERTY

DAMAGE. CONTINUE TO MONITOR THE LATEST FORECASTS. ADDITIONAL

WEATHER INFORMATION IS ON THE WEB AT WWW.WEATHER.GOV/FLAGSTAFF.

&&

$$

AZZ004>007-009>011-039-040-162300-

/O.CON.KFGZ.WI.Y.0004.000000T0000Z-130417T0200Z/

KAIBAB PLATEAU-MARBLE AND GLEN CANYONS-GRAND CANYON COUNTRYCOCONINO PLATEAU-NORTHEAST PLATEAUS AND MESAS HWY 264 NORTHWARDCHINLE VALLEY-CHUSKA MOUNTAINS AND DEFIANCE PLATEAUBLACK MESA AREA-NORTHEAST PLATEAUS AND MESAS SOUTH OF HWY 264-

INCLUDING THE CITIES OF...FREDONIA...PAGE...

GRAND CANYON VILLAGE...SUPAI...CHINLE...KAYENTA...WINDOW ROCK...

GANADO...DILKON

754 AM MST TUE APR 16 2013

...WIND ADVISORY REMAINS IN EFFECT UNTIL 7 PM MST THIS EVENING...

* WINDS...SOUTHWEST 25 TO 35 MPH WITH GUSTS OF 45 TO 55 MPH.

* IMPACTS...WINDS THIS STRONG CAN MAKE DRIVING DIFFICULT... 

 ESPECIALLY FOR HIGH PROFILE VEHICLES. AREAS OF DENSE BLOWING 

 DUST ARE ALSO POSSIBLE...ESPECIALLY ACROSS THE CHINLE VALLEY 

 INCLUDING KAYENTA...MANY FARMS...CHINLE. TRAVEL MAY BE 

 SEVERELY IMPACTED. 

PRECAUTIONARY/PREPAREDNESS ACTIONS...

A WIND ADVISORY MEANS THAT SUSTAINED WINDS OF 30 TO 39 MPH...OR

GUSTS FROM 40 TO 57 MPH...ARE EXPECTED. WINDS THIS STRONG CAN
B-4

MAKE DRIVING DIFFICULT...ESPECIALLY FOR HIGH PROFILE VEHICLES.

CONSIDER SECURING LOOSE BELONGINGS ON YOUR PROPERTY. ADDITIONAL

WEATHER INFORMATION IS ON THE WEB AT WWW.WEATHER.GOV/FLAGSTAFF.

&&

$$

793 

WWUS75 KABQ 161025

NPWABQ

URGENT - WEATHER MESSAGE

NATIONAL WEATHER SERVICE ALBUQUERQUE NM

425 AM MDT TUE APR 16 2013

...VERY WINDY CONDITIONS FOR MUCH OF NORTHERN AND WESTERN NEW

 MEXICO TODAY AND EARLY TONIGHT...

...HIGH WINDS POSSIBLE SOUTH-CENTRAL AREAS WEDNESDAY...

.STRONG SOUTHWEST WINDS WILL RETURN TO MUCH OF NORTHERN AND

CENTRAL NEW MEXICO TODAY AS A BROAD UPPER LEVEL LOW PRESSURE

SYSTEM CROSSING THE GREAT BASIN STEERS THE JET STREAM OVER THE

STATE. PLENTY OF SUNSHINE WILL ENABLE DEEP VERTICAL MIXING IN THE

ATMOSPHERE...WHICH WILL TRANSFER THE STRONGER MOMENTUM ALOFT TO

THE SURFACE WITH WIND GUSTS FROM 45 TO POTENTIALLY OVER 55 MPH.

THE STRONG WINDS WILL DEVELOP DURING THE MORNING HOURS OVER THE

WESTERN MOUNTAINS...AS WELL AS THE WEST CENTRAL HIGHLANDS AND

PLATEAU. THE POTENTIAL EXISTS FOR THE STRONG WINDS TO SPREAD TO

LOCATIONS FARTHER EAST DURING THE AFTERNOON. AREAS OF BLOWING DUST

WILL RESTRICT VISIBILITY AT LOWER ELEVATIONS. WINDS WILL GRADUALLY

WEAKEN WITH SUNSET THIS EVENING...LINGERING LONGEST OVER THE

HIGHER MOUNTAIN PEAKS.

NMZ502-505-506-161800-

/O.UPG.KABQ.WI.Y.0020.130416T1200Z-130417T0300Z/

/O.NEW.KABQ.HW.W.0006.130416T1200Z-130417T0300Z/

CHUSKA MOUNTAINS-WEST CENTRAL PLATEAU-WEST CENTRAL MOUNTAINS425 AM MDT TUE APR 16 2013

...HIGH WIND WARNING IN EFFECT UNTIL 9 PM MDT THIS EVENING...

THE NATIONAL WEATHER SERVICE IN ALBUQUERQUE HAS ISSUED A HIGH

WIND WARNING...WHICH IS IN EFFECT UNTIL 9 PM MDT THIS EVENING.

THE WIND ADVISORY IS NO LONGER IN EFFECT. 

* LOCATION...THE WEST-CENTRAL AND CHUSKA MOUNTAINS...AND WEST

 CENTRAL PLATEAU. THIS INCLUDES THE INTERSTATE 40 CORRIDOR

 BETWEEN THE ARIZONA STATE LINE AND THE CONTINENTAL DIVIDE.

* WINDS...SOUTHWEST 30 TO 40 MPH WITH GUSTS UP TO 60 MPH.

* TIMING...VERY WINDY CONDITIONS ACROSS THE HIGHER TERRAIN NEAR

 DAYBREAK WILL EXPAND TO LOWER ELEVATION LOCATIONS BEGINNING

 AROUND LATE MORNING. STRONG...POTENTIALLY DAMAGING WINDS ARE

 MOST LIKELY BETWEEN 3 PM AND 8 PM.

* VISIBILITY...LOCALLY REDUCED BELOW 1 MILE AT TIMES IN DUST 
B-5

 PRONE AREAS. 

* LOCAL IMPACTS...WIND GUSTS TO 60 MPH WILL RESULT IN EXTREMELY

 HAZARDOUS DRIVING CONDITIONS... ESPECIALLY ON ROADS OR STRETCHES

 OF HIGHWAYS THAT ARE ORIENTED NORTHWEST TO SOUTHEAST. MOTORISTS

 OF HIGH PROFILE VEHICLES SHOULD CONSIDER DELAYING TRAVEL AS

 DANGEROUS CROSS WINDS WILL IMPACT TRAVEL. WINDS OF THIS

 MAGNITUDE MAY RESULT IN PROPERTY DAMAGE. LOOSE OR LIGHT-WEIGHT

 OBJECTS MAY BECOME AIRBORNE.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

REMEMBER...A HIGH WIND WARNING MEANS DAMAGING WINDS ARE IMMINENT

OR HIGHLY LIKELY. SUSTAINED WIND SPEEDS OF AT LEAST 40 MPH OR

GUSTS OF 58 MPH OR MORE CAN LEAD TO PROPERTY DAMAGE.

&&

$$

NMZ501-503-504-509>524-527>529-161800-

/O.EXB.KABQ.WI.Y.0020.130416T1700Z-130417T0300Z/

NORTHWEST PLATEAU-FAR NORTHWEST HIGHLANDS-NORTHWEST HIGHLANDSSAN FRANCISCO RIVER VALLEY-SAN JUAN MOUNTAINS-JEMEZ MOUNTAINSWEST SLOPES SANGRE DE CRISTO MOUNTAINSNORTHERN SANGRE DE CRISTO MOUNTAINS ABOVE 9500 FEET/RED RIVERSOUTHERN SANGRE DE CRISTO MOUNTAINS ABOVE 9500 FEETEAST SLOPES SANGRE DE CRISTO MOUNTAINS-UPPER RIO GRANDE VALLEYLOWER CHAMA RIVER VALLEY-SANTA FE METRO AREAALBUQUERQUE METRO AREA-LOWER RIO GRANDE VALLEYSANDIA/MANZANO MOUNTAINS-ESTANCIA VALLEY-CENTRAL HIGHLANDSSOUTH CENTRAL HIGHLANDS-RATON RIDGE/JOHNSON MESAFAR NORTHEAST HIGHLANDS-NORTHEAST HIGHLANDS425 AM MDT TUE APR 16 2013

...WIND ADVISORY IN EFFECT FROM 11 AM THIS MORNING TO 9 PM MDT

THIS EVENING...

THE NATIONAL WEATHER SERVICE IN ALBUQUERQUE HAS ISSUED A WIND

ADVISORY...WHICH IS IN EFFECT FROM 11 AM THIS MORNING TO 9 PM MDT

THIS EVENING. 

* LOCATION...MUCH OF THE WESTERN TWO-THIRDS OF NEW MEXICO TO

 INCLUDE AREAS ALONG AND WEST OF A LINE FROM RATON TO CLINES

 CORNERS TO SOCORRO. THIS ALSO INCLUDES THE ALBUQUERQUE AND SANTA

 FE METRO AREAS AND SIGNIFICANT PORTIONS OF THE INTERSTATE 25 AND

 INTERSTATE 40 CORRIDORS.

* WINDS...SOUTHWEST 25 TO 35 MPH WITH GUSTS OF 50 TO 55 MPH.

* TIMING...SOUTHWEST WINDS STEADILY INCREASING LATE MORNING TOWARD

 MIDDAY...PEAKING IN STRENGTH BETWEEN 3 PM AND 8 PM BEFORE GRADUALLY

 DIMINISHING BY MID-EVENING.

* VISIBILITY...LOCALLY REDUCED BELOW 1 MILE AT TIMES IN DUST 

 PRONE AREAS. 
B-6

* LOCAL IMPACTS...STRONG CROSS WINDS WILL IMPACT TRAVEL...

 ESPECIALLY ON ROADS OR STRETCHES OF HIGHWAYS ORIENTED NORTHWEST

 TO SOUTHEAST. LOOSE AND LIGHT-WEIGHT OBJECTS MAY BECOME

 AIRBORNE. BLOWING DUST IMPACTS WILL LIKELY BECOME SIGNIFICANT IN

 DUST PRONE LOCATIONS...ESPECIALLY ALONG THE RIO GRANDE

 VALLEY...AND ESTANCIA BASIN.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

MOTORISTS SHOULD EXERCISE CAUTION WHILE TRAVELLING. SUDDEN GUSTS

OF WIND MAY CAUSE YOU TO LOSE CONTROL OF YOUR VEHICLE. EXTRA

ATTENTION SHOULD BE GIVEN TO CROSS WINDS.

&&

$$

NMZ507-508-161800-

/O.CON.KABQ.WI.Y.0020.130416T1200Z-130417T0300Z/

WEST CENTRAL HIGHLANDS-SOUTHWEST MOUNTAINS425 AM MDT TUE APR 16 2013

...WIND ADVISORY REMAINS IN EFFECT UNTIL 9 PM MDT THIS EVENING...

* LOCATION...THE SOUTHWEST MOUNTAINS TO INCLUDE THE UPPER GILA

 REGION...AND WEST CENTRAL HIGHLANDS.

* WINDS...SOUTHWEST 25 TO 40 MPH WITH GUSTS UP TO 55 MPH.

* TIMING...SOUTHWEST WINDS STEADILY INCREASING LATE MORNING TOWARD

 MIDDAY...PEAKING IN STRENGTH BETWEEN 3 PM AND 8 PM BEFORE GRADUALLY

 DIMINISHING BY MID-EVENING.

* VISIBILITY...LOCALLY REDUCED BELOW 1 MILE AT TIMES IN DUST 

 PRONE AREAS. 

* LOCAL IMPACTS...STRONG CROSS WINDS WILL IMPACT TRAVEL...

 ESPECIALLY ON ROADS OR STRETCHES OF HIGHWAYS ORIENTED NORTHWEST

 TO SOUTHEAST. LOOSE AND LIGHT-WEIGHT OBJECTS MAY BECOME

 AIRBORNE. BLOWING DUST IMPACTS WILL LIKELY BECOME SIGNIFICANT IN

 DUST PRONE LOCATIONS...ESPECIALLY INTERSTATE 40 NEAR THE RIO

 PUERCO. 

PRECAUTIONARY/PREPAREDNESS ACTIONS...

MOTORISTS SHOULD EXERCISE CAUTION WHILE TRAVELLING. SUDDEN GUSTS

OF WIND MAY CAUSE YOU TO LOSE CONTROL OF YOUR VEHICLE. EXTRA

ATTENTION SHOULD BE GIVEN TO CROSS WINDS.

&&

$$

NMZ525-526-539-540-161800-

/O.NEW.KABQ.HW.A.0006.130417T1600Z-130418T0300Z/

UPPER TULAROSA VALLEY-SOUTH CENTRAL MOUNTAINSEASTERN LINCOLN COUNTY-SOUTHWEST CHAVES COUNTY-
B-7

425 AM MDT TUE APR 16 2013

...HIGH WIND WATCH IN EFFECT FROM WEDNESDAY MORNING THROUGH

WEDNESDAY EVENING...

THE NATIONAL WEATHER SERVICE IN ALBUQUERQUE HAS ISSUED A HIGH

WIND WATCH...WHICH IS IN EFFECT FROM WEDNESDAY MORNING THROUGH

WEDNESDAY EVENING. 

* LOCATION...MUCH OF LINCOLN AND SOUTHWEST CHAVES COUNTIES TO

 INCLUDE RUIDOSO...CAPITAN...AND DUNKEN.

* WINDS...WEST TO SOUTHWEST 30 TO 40 MPH WITH GUSTS TO 60 MPH. 

* TIMING...STRONG...POTENTIALLY DAMAGING WINDS ARE EXPECTED

 BETWEEN 11AM AND 8PM WEDNESDAY. 

* VISIBILITY...LOCALLY REDUCED BELOW 1 MILE AT TIMES IN DUST PRONE

 AREAS. 

* LOCAL IMPACTS...WIND GUSTS TO AROUND 60 MPH WILL RESULT IN

 EXTREMELY HAZARDOUS DRIVING CONDITIONS... ESPECIALLY ON ROADS OR

 STRETCHES OF HIGHWAYS THAT ARE ORIENTED NORTH TO SOUTH.

 MOTORISTS OF HIGH PROFILE VEHICLES SHOULD CONSIDER DELAYING

 TRAVEL AS DANGEROUS CROSS WINDS WILL IMPACT TRAVEL. WINDS OF

 THIS MAGNITUDE MAY RESULT IN PROPERTY DAMAGE. LOOSE OR LIGHT-

 WEIGHT OBJECTS MAY BECOME AIRBORNE. BLOWING DUST IMPACTS WILL BE

 MOST CRITICAL NEAR AND WEST OF CARRIZOZO.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

REMEMBER...A HIGH WIND WATCH MEANS CONDITIONS ARE FAVORABLE FOR

A POTENTIALLY DAMAGING HIGH WIND EVENT IN AND CLOSE TO THE WATCH

AREA. SUSTAINED WIND SPEEDS OF AT LEAST 40 MPH OR GUSTS OF 58 MPH

OR MORE CAN LEAD TO PROPERTY DAMAGE. MONITOR THE LATEST FORECASTS

AT WEATHER.GOV/ABQ...LISTEN TO NOAA WEATHER RADIO OR YOUR

FAVORITE MEDIA OUTLET.
B-8

Blowing Dust Advisory

Issued for western and south-central Colorado

Issued by Colorado Department of Public Health and Environment

Issued at 9:30 AM Tuesday, April 16, 2013

Affected Area: western and south-central Colorado, including Moffat, Rio Blanco, Garfield, 

Mesa, Delta, Montrose, Ouray, San Miguel, Dolores, San Juan, Montezuma, La Plata, Hinsdale, 

Mineral, Archuleta, Cornejos, Rio Grande, Saguache, Alamosa, and Costilla counties. Cities 

include, but are not limited to Craig, Meeker, Rifle, Grand Junction, Delta, Montrose, Telluride, 

Cortez, Durango, Pagosa Springs and Alamosa.

Advisory in Effect: 10:00 AM Tuesday 4/16/2013 to 8:00 PM Tuesday 4/16/2013

Public Health Recommendations: If significant blowing dust is present and reducing visibility to 

less than 10 miles across a wide area, People with heart or lung disease, older adults, and 

children in the affected area should reduce prolonged or heavy indoor and outdoor exertion.