NOAA TECHNICAL MEMORANDUM 

NWS WR-282 

HAZARDOUS WEATHER CLIMATOLOGY FOR ARIZONA 

by: 

Craig Shoemaker 

Jeffrey T. Davis 

February, 2008 
ii 

And is approved for publication by 

Scientific Services Division 

Western Region 

Andy Edman, Chief 

Scientific Services Division 

Salt Lake City, UT 

 
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Hazardous Weather Climatology for Arizona 

By 

Craig Shoemaker 

and 

Jeffrey T. Davis 

National Weather Service 

Tucson, Arizona 

February 28, 2008 
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Table of Contents

List of Figures.................................................................................... v

I. Introduction ............................................................................. 1

II. Methodology ........................................................................... 1

A. Data....................................................................................................1 

B. Data Biases and Discrepancies ..........................................................1 

C. Climate Divisions...............................................................................2

III. Overview of Results ................................................................ 2

A. Role of Thunderstorms in Hazardous Weather across Arizona.........2 

B. Ranking of Hazardous Weather in Arizona.......................................3 

IV. Severe Weather Events............................................................ 3

A. Tornadoes...........................................................................................4 

B. Hail.....................................................................................................5 

C. Wind...................................................................................................6 

V. Significant Weather Events..................................................... 7

A. Flash Floods and Floods ....................................................................7 

B. Dust Storms........................................................................................8 

C. Lightning .............................................................................. 8 

D. Dust devils and Gustnadoes...............................................................9 

VI. Other Weather Related Events ................................................ 9

A. Drought ................................................................................ 9 

B. Wildfires.............................................................................10 

C. Snow and Ice .......................................................................10 

 

VII. Summary ...............................................................................11

VIII. References .............................................................................13

 
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List of Figures

Figure 1: Example of Storm Data, historical, and spotter reports skewed toward cities 

and major highways. 

Figure 2: Example of the Storm Data discrepancy for the 1970 Labor Day Weekend 

storm. No deaths were reported in the Storm Data publication for this event. 

Figure 3: Arizona climate regions as defined by Sellers and Hill (1974) 

Figure 4: Injures and fatalities in Arizona sub-divided by weather event for the period of 

1955 to 2004 

Figure 5: Total tornadoes in each county from 1950 to 2004 

Figure 6: Mogollon Rim Convergence Zone (MRCZ) 

Figure 7: Tornado frequency by F scale from 1950 to 2004 

Figure 8: Tornado frequency by month and F scale from 1950 to 2004 

Figure 9: Tornado frequency by month from 1950 to 2004 

Figure 10: Tornado frequency by month and climate region from 1950 to 2004 

Figure 11: Tornado frequency by hour from 1950 to 2004 

Figure 12: Secondary peak in the annual tornado frequency for the Southwest and 

Northeast climate regions for the period of 1950 to 2004 

Figure 13: The percentage of hail events by County from 1955 to 2004 

Figure 14: Hail frequency by month and size from 1955 to 2004 

Figure 15: Hail frequency by hour from 1955 to 2004 

Figure 16: Total thunderstorm wind events by climate region from 1955 to 2004 

Figure 17: Thunderstorm wind frequency by month from 1955 to 2004 

Figure 18: Thunderstorm wind frequency by hour from 1955 to 2004 

Figure 19: Thunderstorm wind frequency by hour and climate region from 1955 to 2004 

Figure 20: Flash flood and flood frequency by month from 1955 to 2004 

Figure 21: Flash flood and flood frequency by hour form 1955 to 2004 

Figure 22: Flash flood and flood frequency by month and climate region from 1955 to 

2004 

Figure 23: The areal extent of some historically significant floods in Arizona 

Figure 24: Tropical system tracks over the southwestern U.S. and eastern Pacific from 

1958-2003 

Figure 25: Frequency of dust storm fatalities by month from 1955 to 2004 

Figure 26: Average number of thunderstorm days per year for the United States 

Figure 27: The ten year flash density for the U.S from 1996-2005 

Figure 28: Lightning Fatalities and Injuries by month from 1955 to 2004 

Figure 29: Rate of lightning casualties (deaths and injuries combined) per population 

ordered by state from 1959 to 1994 

Figure 30: Rate of lightning fatalities per population ordered by state from 1997 to 2006 

Figure 31: A close up of the ten year flash density for Arizona from 1996-2005 

Figure 32: Flash density key

. 
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Figure 33: Flash densities (flashes per 100 km2 per monsoon season) for 20 km x 20 

km boxes during all hours for 1985-1990 

Figure 34: National Palmer Drought Severity Index 1895-1995 

Figure 35: Drought Extent, Length and Composite Palmer Drought Severity Indexes 

for Arizona 1950-1995 

Figure 36: Aerial extent of historical droughts in Arizona

Figure 37: Arizona statewide water year precipitation, 1896-2005 

Figure 38: Wildfire Hazard Areas Map

Figure 39: Fire Hazard is based upon factors such as fuel types and condition, natural 

fire regimes, and topography and the influence of structures. 

Figure 40: Fire hazard key 

Figure 41: Mean annual snowfall for Arizona for the period 1961-1990 

Figure 42: Key for the mean annual snowfall for Arizona for the period 1961-1990 

Figure 43: Mean annual snowfall days for Arizona for the period 1961-1990 

Figure 44: Key for the mean annual snowfall days for Arizona for the period 1961-

1990 

Figure 45: Snow and Ice by month from 1955 to 2004
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I. Introduction 

Providing expedient severe weather warnings to save lives and property is the most important 

mission provided by National Weather Service offices in Arizona. This study discusses 

numerous hazardous weather types including tornadoes, hail, wind, flash floods and floods, 

lightning, dust storms, dust devils, extreme temperatures, drought, wildfires and winter storms. 

A comprehensive understanding of the state’s hazardous weather climatology will better 

prepare forecasters in anticipating the timing, strength, location and nature of hazardous 

weather. This climatological information will also be useful to emergency managers and 

private citizens in understanding the characteristics of severe weather across Arizona. 

Therefore, the purpose of this study is to quantitatively describe the hazardous weather 

climatology for Arizona using reports from 1950 to 2004 for tornadoes and 1955 to 2004 for 

other events. 

II. Methodology 

A. Data 

This paper is a compilation of nearly five decades of meteorological data formed from multiple 

hazardous weather data sources. Tornadoes, hail, high winds, lightning, flooding, severe 

winter-weather cases, extreme heat and cold outbreaks are included. Seven sources of 

information were used to compile the severe weather information: 

• National Weather Service's (NWS) Storm Prediction Center (SPC) Database from 1950 

to 2004 

• National Climatic Data Center's (NCDC) Storm Data (NOAA 1955-2004) NCDC 

Storm Events Database 

• National Highway Traffic Safety Administration’s (NHTSA) Fatality Analysis 

Reporting System (FARS) from 1994 to 2004 

• University of Arizona Storm Database 

• Arizona Department of Health Services’ (ADHS) Division of Public Health Services 

• Report on Injury Mortality among Arizona residents (1990-2000) 

• Arizona Climate: The First Hundred Years (Sellers, Hill and Sanderson-Rae, 1985). 

Data analysis using ArcView GIS version 3.1 allowed for the plotting of the above mentioned 

databases to determine trends of events with regards to topography along with seasonal and 

diurnal frequencies. 

B. Data Biases and Discrepancies 

The low population density (45.2 people per sq mi) in Arizona (U.S. Census, 2000) has likely 

resulted in many severe weather events not being reported, especially those which occur away 

from the high density population centers of the larger cities in Arizona. Additionally, there is a 

significant bias to reports along roadways in predominantly rural areas. Therefore, it is 

important to note that the events from which statistics in this study are generated are actually a 

subset of all significant events which have occurred in Arizona. Figure 1 illustrates the bias of 

wind events to population centers and along or near roads. 
2 

Many database discrepancies were encountered as the study progressed. One example of this is 

with the Labor Day weekend storm of 1970, which was a flash flood and flood event caused by 

tropical storm Norma. The official Storm Data report shows no deaths or injuries as depicted in 

Figure 2. However, the Sellers et al. (1985) report shows 23 deaths caused by the system. 

Further investigation shows that indeed there were 23 deaths. Yet, another discrepancy can be 

seen in the event reporting methods used in official Storm Data entries over the years. When 

severe weather occurs on a statewide scale, it is often reported in broad terms (central, 

southern, northern) instead of the preferred county break down (Pima, Yuma, Maricopa). This 

is especially the case for events prior to the NWS modernization and associated restructuring in 

the 1990’s. The numerous data sources used in this study have sorted out such discrepancies 

and lead to a more comprehensive dataset which is summarized in this paper. 

C. Climate Divisions 

Arizona is the sixth largest state in the United States at just over 114,000 sq mi. and elevations 

varying from under 300 ft to over 12,000 ft (Sellers and Hill, 1974). This topographical 

variation over a vast spatial area yields an extreme collection of climate regimes with 

extraordinarily diverse weather. Therefore, for this study Arizona has been broken down into 

six climate regions, originally developed by Sellers and Hill (1974). Figure 3 shows a map of 

the six different climate regions used in this study. These climate divisions better highlight the 

seasonal and diurnal frequencies that would be normally hidden by the typical county or the 

NWS County Warning Area (CWA) breakdown. 

The Northeast region encompasses the area from the Little Colorado River northeast, including 

the Painted Desert. The Plateau zone stretches the length of the Mogollon rim from the Kaibab 

Plateau and Grand Canyon to the White Mountains. The Northwest region covers the Colorado 

River valley over the northwest part of the state. The Central region includes areas along the 

southern rise to the Mogollon rim. The Southwest region encompasses the lower desert areas 

including Phoenix and Yuma. The Southeast region covers eastern Pima and Pinal counties, 

eastward to the New Mexico border. Each of these regions is affected differently by synoptic 

and meso-scale systems and the resulting monsoonal and winter-time precipitation. 

III. Overview of Results 

A. Role of Thunderstorms in Hazardous Weather across Arizona 

Thunderstorms are responsible for a large percentage of the hazardous weather observed in 

Arizona. The thunderstorm season, which is driven by the North American Monsoon, 

encompasses the majority of annual thunderstorm activity. The North American Monsoon is a 

regional-scale circulation that develops over southwest North America during the months of 

July through September. It is associated with a dramatic increase in moisture that occurs over 

what is normally an arid region of North America, as a shift in the mid-level flow from 

westerly to easterly, occurs (Adams and Comrie, 1997). 

The thunderstorm season in Arizona is fairly well defined, although it varies considerably 

between northern and southeastern sections of the state due to elevation. The thunderstorm 

season generally begins over the southeast portion of the state in late June to early July 

(Tucson’s average start date is around July 3rd and Douglas is the last week in June). Elevations 
3 

above 5,000 feet generally receive their first thunderstorms a week earlier than the above 

mentioned dates. A gradual decrease in thunderstorm activity occurs in September and 

October, with some seasonal variability due to tropical activity. In contrast, across northern 

Arizona (including Flagstaff) the thunderstorm season typically does not become established 

until mid or late July. Over central Arizona, including the Plateau region and Mogollon rim, 

the season usually gets started in early July, with the average at Phoenix around the 7th of July. 

Thunderstorms also have different characteristics within the state. Across the higher elevations 

(above 5,000 feet) hail, generally small, and heavy rains are most prevalent. As the 

thunderstorms progress off the mountains into valley locations, high winds and dust storms 

become a major concern. This is a result of the elevation change, which allows for a large 

amount of the rainfall to evaporate before reaching the surface, causing more momentum as 

rain-cooled air accelerates to the surface. This process can result in numerous micro bursts as 

these thunderstorms progress into valleys. The drastically warmer temperatures over the valley 

areas cause the majority of hail stones to melt before reaching the surface. Flash flooding does 

occur due to heavy rainfall with valley thunderstorms, especially over urban areas. A great 

flood threat also results when heavy rain falling at higher elevation flows into lower elevation 

rivers and washes.

B. Ranking of Hazardous Weather in Arizona 

Although thunderstorms produce a large percentage of weather hazards, the greatest hazard in 

Arizona is extreme temperature which is responsible for the largest number of fatalities. Figure 

4 shows the frequency of injures and fatalities in Arizona by weather type for the period of 

1955 to 2004. For the extreme heat/cold category, the highest component is extreme heat. It is 

very likely that heat is an even greater killer than the data depicts. Untold numbers of illegal 

immigrant deaths go unreported yearly, so the fatalities may be significantly higher (Keim et 

al, 2006). Available data is only over a ten year period (1990-2000), making it even more 

impressive compared to other weather events. Extreme heat will not be examined in later 

sections of this paper due to the unreliability of casualty statistics before 1990, and the vague 

cause of death reports associated with heat victims. 

Floods and flash floods are the next most dangerous hazards when considering injuries and 

fatalities, followed closely by dust storms. Tornadoes and thunderstorm winds are responsible 

for a number of injuries across the state, however only three fatalities due to tornadoes have 

been reported. The greatest number of fatalities outside of extreme heat occurs from May to 

September, primarily caused by dust storms, flash floods and lightning. Most injuries occur 

during the months of May through September, with thunderstorm wind in addition to dust 

storms, flash floods and lightning as the major contributors to the totals. 

IV. Severe Thunderstorm Events 

A. Tornadoes 

Tornadoes are a more common occurrence in Arizona than most people are aware, primarily 

over the Central valleys and Plateau regions. For the state, the average of reported tornadoes is 

approximately 4 per year. Figure 5 shows the distribution of reported tornadoes by county from 

1950 to 2004. These statistics reveal that the lower valleys of Maricopa, Pinal and Pima 
4 

counties, along with the little Colorado River valley, are well-defined maxima for tornadoes. 

Tornado development in Arizona is often complicated, since they rarely form under textbook 

conditions. Instead, many Arizona tornadoes are of the non-supercell type; Arizona tornadoes 

are not associated with low or mid-level mesocyclones, but are formed by thunderstorms 

interactions with preexisting boundary layer circulations. An example of this would be the 

stretching of a preexisting dust-devil, gustnado or lesser circulation into the vertical by a 

thunderstorms updraft. This causes the circulation to tighten and spin faster, allowing for a 

brief spin up of tornadic wind speeds. Several documented cases of this type have come to light 

over the past several years, with the onset of digital cameras and camcorders. One such well 

documented area for non-supercell tornadoes is the region between the Little Colorado River 

Valley and the Mogollon Rim, known as the Mogollon Rim Convergence Zone (MRCZ) 

(Blanchard, 2000). This terrain driven convergence is a region of enhanced thunderstorm 

development and vertical vorticity. Although, MRCZ has been documented by a recent study 

(Figure 6), many smaller zones of this type exist across the state. As a result tornado detection 

and verification is often a distorted practice across the state. 

Despite the 196 reported tornadoes in Arizona, only 3 fatalities have been reported since 1950, 

while 139 injuries were documented. The low number of fatalities can be in part explained by 

the strength of tornadoes found across the state. Wind speeds in tornadoes vary from 40 mph to 

318 mph (F0 to F5 on the Fujita scale). Since the mid 1980's, tornado strength has been 

measured using the Fujita Scale, or F scale (Abbey and Fujita, 1975). This scale ranks 

tornadoes by damage intensity, with F0 being the weakest and F5 the strongest. This scale was 

developed to create a relationship between tornado wind strength and the expected structural 

damage accompanying this wind. Since there is a highly varying degree of structural integrity 

of buildings across Arizona, the application of the Fujita scale is difficult to apply. In Figure 7, 

the reported Arizona tornadoes are listed by F scale frequency, and Figure 8 shows the 

distribution by month and F scale. Certainly, the strength of many tornadoes is not known, but 

less than 7% of the tornadoes with a known intensity are in the strong category (F2 or F3). 

Given this information, a high percentage of reported tornadoes in this state are weak, either F0 

or F1. 

Figure 9 depicts the monthly frequency of all reported tornadoes and Figure 10 shows the 

distribution by month and region. Over 95% of tornadic storms occur in May through 

September, with about 60% occurring in July through September. Tornadoes were reported in 

all months, F2 tornadoes were mainly recorded May through October, except for one 

occurrence in January. Figure 11 shows the frequency of tornadoes by hour, with the majority 

of tornadic storms occurring between 11:00 AM and 11:00 PM MST. The number of tornadoes 

that occur after dark (8:00 PM MST) is very small, with no reports of tornadoes between 2:00 

AM and 7:00 AM MST. 

Secondary tornado peaks occur for Southwest and Northeast climate regions as shown in 

Figure 12. In the Southwest region, this secondary peak occurs from January through March in 

association with strong late winter storm systems. Over the Northeast region two peaks show 

up outside of the monsoon season: one from April through June, and the other September and 

October. To further substantiate these peaks, data from the Four Corners region of New 

Mexico, Colorado and Utah are included in Figure 12 as well. Over the Northeast Arizona zone 
5 

this peak is attributed to the interaction of residual monsoonal moisture with late summer-early 

fall storm systems (Adams and Comrie, 1997). These transitional events are often 

characterized by high shear and marginally unstable environments (Blanchard, 2006). 

B. Hail 

The NWS defines a hail event as severe when large hail is at least 0.75 of an inch in diameter. 

Hail ranks only as the third most frequent hazardous weather type, but is still responsible for a 

considerable percentage of property and crop damage. The state averages 12 severe hail events 

per year. Hail is not a major threat for bodily harm in the state; no fatalities and seven injuries 

have been reported due to hail. These numbers are the lowest of any severe weather type. High 

freezing levels tend to diminish the threat of large hail across the state, since a significant 

amount melting occurs as hail stones fall to the surface. High cloud bases also lead to some 

sublimation of the stones, further reducing the size seen at ground level (Hsin-mu Lin,et al. 

2005). Frequent small hail occurrences are seen at higher elevations, but are generally below 

severe levels, due to weaker updraft strengths with mountain thunderstorms. The percentage of 

hail events by county for Arizona is depicted in Figure 13. 

A significant bias towards population centers is seen with hail reports. This bias should not be 

a surprise given the visual conformation needed for hail measurements. In unpopulated areas, 

either the hail melts before a measurement can be made, or the damage from the melted hail is 

attributed to another severe weather element such as wind. Although these figures show the 

highest severe hail frequencies over Maricopa, Pinal, Pima and Coconino counties it is likely 

many of the lower frequency counties such as Graham and Greenlee counties have an equal or 

greater severe hail frequency. 

Figure 14 shows the number of hail reports by month and by size. Damaging or severe hail 

(0.75 to 1.50 inches) is most common in June through August, as is very large hail (over 1.50 

inches); although a significant number of very large hail reports also occur in September. The 

size of some hail reports are not known, but were included in Storm Data because they caused 

significant crop and/or property damage or had a significant accumulated depth. These reports 

are included in this study due to their likelihood of being severe hail. Figure 15 reveals 

damaging hail is most likely to fall in the afternoon and early evening, as is the case with 

tornadoes. Just over 70% of the reported severe hail events fell between 2:00 PM and 6:00 PM 

MST. The largest hail stone reported in the state is 4.50 inches, which is softball size. This 

occurred in Mayer, Yavapai County, on September 28, 1995 (Storm Data). 

C. Wind 

A wind event is considered severe when speeds of 58 mph or greater are measured or 

estimated, or produce significant damage. Arizona averages 29 severe wind events per year, 

with the greatest concentration over the southern most climate regions. The number of reported 

thunderstorm wind events by climate region is shown in Figure 16. Thunderstorms moving off 

the higher terrain into the hot, dry desert tend to produce stronger downdrafts due to extreme 

evaporation rates of precipitation and greater descent distance. Therefore, severe downbursts 

and outflow boundaries are more common over these regions. Additionally, wet microbursts 

also occur over these areas, especially during the mid and late monsoon season. However, 

isolated events can occur with strong baroclinic systems outside of the monsoon season. These 
6 

events are typically most common over the west and northwest. Dry microbursts occur when 

rain falls through an extremely dry atmosphere and evaporates, causing rapid cooling of the air. 

This air rapidly desends and accelerates as it nears the surface. Very little if any rainfall 

reaches the ground; instead the cooled air spreads out in the form of strong and occasionally 

damaging winds. Wet microbursts occur during very heavy precipitation, typically in warm 

and moist atmopheres. They rely on drag of precipitation to accelerate the air towards the 

surface. The air then spreads out, as it impacts the ground, in the form of strong and 

ocassionally damaging winds.

Arizona thunderstorm wind events are mainly clustered over a two month period: July and 

August, shown in Figure 17. This should not be a surprise given this is the peak of the 

monsoon. The slightly higher occurrence rate in September is predominantly over the first half 

of the month when the monsoon is generally still active. The diurnal cycle of thunderstorm 

wind events is clustered from 3:00 PM to 9:00 PM MST, with the peak at 7:00 PM MST as 

shown in Figure 18. This timeframe is to be expected, given the diurnal nature of monsoonal 

thunderstorms and their dependence on solar heating. Figure 19 shows that hourly events are 

not uniform over the state. Instead, severe wind events have clearly defined time ranges for 

each climate region. The time offsets are due to how daily heating and moisture interact with 

the complex terrain of the state. This diurnal difference is not surprising since thunderstorms 

form over the higher terrain earlier in the day. Convection then typically shifts into the valleys 

and lower desert areas in the late afternoon and evening. The most intense and direct solar 

heating occurs over the mountains during the morning hours. This differential heating produces 

sufficient buoyancy for earlier thunderstorm development over the mountains. Intense surface 

heating during the afternoon, allows convection and accompanying damaging winds to 

transition into valleys and lower deserts by evening, providing adequate moisture is in place. 

The highest thunderstorm associated wind speed measured in the state is 175 knots. This 

occurred in Spring Valley which is in Yavapai County on September 6, 1996 at 11:15AM MST 

(Storm Data). 

V. Significant Weather Events 

A. Flash Floods and Floods 

Flash floods are defined by the NWS as a quick response to heavy rainfall in streams, rivers, or 

any flood prone area, six hours or less after the heavy rain started. Flood events are defined as 

longer lasting events, with rivers rising above flood stage over 6 hours to many days. For this 

study flash floods and floods will be combined, due to the broad grouping of numerous flood 

events with flash floods before NWS modernization in the mid 1990’s. A great number of 

events prior to modernization are simply recorded as statewide flooding, leaving no way to 

differentiate between flash and river flooding. 

In Arizona, the greatest numbers of flood events during the monsoon season are of the flash 

flood type. Therefore, flood events occurring during the monsoon period (July-September) will 

be referred to as flash floods for this study. In Arizona, flooding ranks second to extreme 

temperatures in causing fatalities. Over the period 1959-1999, Arizona ranked tenth in the 

nation in flooding deaths per million people (NCDC). In the western United States, the 

monthly distribution of flood events displays a summer maximum due to thunderstorms, and a 
7 

secondary winter maximum (January-March) due to winter storms. The monthly distribution of 

floods in Arizona is shown in Figure 20, and reveals a strong association with the summertime 

North American Monsoon, with nearly three fourths of floods occurring from July through 

September. Unlike much of the western United States, the secondary maximum is much 

smaller during the winter months. Figure 21 shows the distribution of floods by hour. Most of 

the flash floods occur between 4:00 PM and 7:00 PM similar to the peak hours of severe hail 

and tornadoes. 

Intense rainfall over a short period of time can result in large amounts of water surging through 

canyons in the mountains of Arizona; however, the valleys receive numerous flash floods as 

well. Of particular concern in valley locations are normally dry washes, which become raging 

rivers in a matter of minutes due to intense rainfall. These dry washes are very common over 

desert terrain and crisscross many urbanized areas, exacerbating flash flood dangers. In Figure 

22, the number of reported flash floods and floods for each climate region and the monthly 

distribution is shown. Flash flood frequencies are greatest over the Southeast followed by the 

Southwest climate region. These two regions contain the majority of Arizona’s population, 

with the greatest flash flood occurrences in the Tucson and Phoenix metropolitan areas over 

the July through September period. The Southeast climate zone has a flash flood frequency 

nearly equal to all other zones combined for the months of July and August. Finally, slight 

secondary maxima can be seen over the Northwest, Plateau, Central and Southwest climate 

zones’ January through March due to winter storms. Although, these events tend to be less 

frequent, they are typically more widespread and quite destructive as they usually involve main 

stem river flooding. Some historically significant aerial flood events and recurrence intervals 

are shown in Figure 23. 

Concealed in the data is flooding associated with tropical systems. Tropical systems are 

infrequent over the state, occurring only once every five years, as west coast troughs typically 

lack the amplitude to pull the systems northward. The low proportion of tropical systems 

impacting the southwestern United States is illustrated in Figure 24. 

However, when west coast troughs have the strength to pull tropical systems north; the effects 

can be devastating. During these events flash flooding and main stem river flooding often 

occur simultaneously. The deadliest natural disaster in Arizona’s history was Tropical Storm 

Norma on Labor Day 1970. Flooding from Norma resulted in 23 deaths as reported by Sellers 

et al. (1985). 

B. Dust Storms 

Dust storms are often underestimated as significant weather events. They rank only behind the 

extreme heat/cold and flood categories for causing deaths and injuries. Most of these deaths are 

due to multi-car pileups on roadways and interstates. In Arizona, several different weather 

regimes are associated with major dust storms. Brazel and Nickling (1986) identified four of 

them: (1) frontal, (2) thunderstorm, (3) tropical disturbance, and (4) upper level trough and/or 

cut-off low. 

Early season monsoon thunderstorms are the most notorious for producing deadly dust storms. 

July is clearly the most deadly dust storm month across the state, with nearly double the 
8 

fatalities compared to other months depicted in Figure 25. July is the transition month from dry 

season (March-June) to monsoon season. Thunderstorms during the first few weeks of the 

monsoon produce very little rainfall, as much of the lower atmosphere remains dry. Much of 

the rain with early monsoon season thunderstorms evaporates before reaching the surface. This 

leads to dry downburst winds, which organize into larger and strong outflows. These strong 

winds pick up the dry soil, dust and sediments pre-conditioned by the dry season, often 

producing long lasting dust storms with visibilities near zero. Typically, these severe storms 

frequently referred to as “haboobs” (hə-ˈbüb), affect the Phoenix metropolitan area and 

surrounding desert areas during the monsoon season. 

C. Lightning 

Thunderstorms and lightning are a common occurrence in Arizona, mainly during the summer 

months. Arizona has an annual thunderstorm frequency comparable to many perceived 

thunderstorm rich Central Plains states. Total thunderstorm days range from fewer than 10 

days along the lower Colorado River valley to 80 days over the White Mountains Figure 26. 

However, the majority of this thunderstorm activity is compacted into a three-month period 

(July-September). Similarly, thunderstorm lightning flash density shows a favorable 

comparison to many Plains States; with a maximum over the Mogollon rim and much of 

southeast Arizona as shown in Figure 27. Arizona lightning fatalities and injuries fall into this 

timeframe as well (July-September), with August the peak month as shown in Figure 28. The 

three month period of February-April along with December is devoid of any lightning 

casualties. Despite the relatively high flash density, Arizona ranks in the middle of the pack 

nationally for lightning casualties per capita Figure 29 and Figure 30. A major reason for this is 

the major population centers of Phoenix and Yuma are in lower flash density areas, unlike 

much of the rest of the state Figure 31 and Figure 32. Of the major population centers Tucson 

is located in the most lightning flash dense zone (2-8 flashes/sq. km/yr) as depicted in Figure 

33. Still, the 80 fatalities and 200 injuries that have occurred over the state are quite 

significant. 

D. Dust Devils and Gustnadoes 

Although some may find it odd and even a bit humorous to include dust devils in a hazardous 

weather climatology, facts point to a destructive side of the often fair weather, benign vortex. 

Winds of dust devils can reach up to 70 miles per hour, which is certainly strong enough to do 

minor to moderate damage. Officially, four dust devil reports are listed in Storm Data; 

unfortunately no dust devils have been listed before 1994 or after 1997. Many dust devils in 

Storm Data are cross listed, combined, or misclassified as dust storms, making it nearly 

impossible to differentiate between the two. Of the four listed, two caused considerable 

damage in Tucson. 

Dust devils are generally small vortexes not associated with thunderstorms, which are made 

visible by rotating clouds of dust or debris. The key here is that they are not associated with 

thunderstorms and more specifically do not extend upward to the cloud base of a thunderstorm. 

Dust devils form due to strong surface heating during hot weather. Strong heating from the sun 

causes the surface to become much warmer than air above the surface. Additionally, uneven 

heating of the surface occurs, certain terrain and vegetation type’s heat up more and faster than 

others. As a result, the warm air has a tendency to rise in bubbles. As these bubbles of warm air 
9 

rise, cooler air from above and to the sides of the bubble rushes around and below to fill the 

void. This inrush of air can happen in a somewhat uneven manner, and as it reaches the center 

of the void filled by the bubble of rising air, can begin to spin (Renno et al. 1998). The 

combination of lower air pressure and heating causes the air, dust and debris inside the dust 

devil to rise. Wind speeds near the centers of dust devils can range from just a few miles per 

hour to perhaps as much as 70 miles per hour. 

In Arizona gustnadoes are probably quite common among the strongest thunderstorm-produced 

gust fronts. Gustnadoes are short-lived, ground-based, shallow, vortexes that develop on a gust 

front associated with either thunderstorms or showers. They may only extend from 30 to 300 

feet above the surface. Again, the key here is there will be no connection with the cloud base. 

They may be accompanied by rain, but usually are only visible as a debris cloud or dust whirl 

at or near the ground. Wind speeds can reach 60 to 80 mph, resulting in significant damage, 

similar to that of a F0 or F1 tornado. However, gustnadoes are not considered tornadoes. 

Gustnadoes are not associated with storm-scale rotation (they do not extend up into the cloud) 

that is involved with true tornadoes. They are more likely to be associated visually with a shelf 

cloud that is found on the forward side of a thunderstorm near strong outflow winds.

VI. Other Weather Related Events

A. Drought 

Drought is defined most succinctly as insufficient water to meet needs (Redmond, 2002). 

Many people are unaware that it is possible to have a drought in the desert; which is an arid 

environment. Therefore, Arizona droughts seem to take people by surprise, even though they 

have been worsening for years. The composite Palmer Drought Severity Index (1895-1995 in 

Figure 34 and 1950-1995 in Figure 35) shows that drought across the state has been steadily 

worsening over the past several decades. A drought is often looked upon as a long term 

problem until it affects us in the short term and our everyday life. Figure 36 shows the areal 

extent of historic droughts and their recurrence interval in years. A federal emergency 

declaration (allows government aid) was issued for the 1973-77 drought by Federal Emergency 

Management Agency (FEMA). Figure 37 shows the Arizona statewide water year 

precipitation from 1896 to 2005. The red highlighted regions are periods of low precipitation. 

Notice how they correspond favorably to historic droughts. It is difficult to measure state 

drought effects in monetary or casualty statistics since its effects are subtle, gradual and often 

linked to some other hazardous event (such as heat and wildfires). However, it is almost certain 

that when considering a drought’s entire duration, its damaging effects are comparable or even 

greater than other more visible hazardous weather types. 

B. Wildfires 

Wildfires pose an increasingly significant threat to life, property and the economy of Arizona. 

High impact wildfires have been far more common over the last decade than previous several 

decades. In fact, three of the most serious wildfires, Rodeo-Chediski in 2002, Aspen in 2003, 

and Cave Creek in 2005 have occurred over the past five years. Both the Rodeo-Chediski and 

Aspen fires were given the dubious distinction of being declared major disasters by FEMA. 

These are the only two fires to be given this classification in the state’s fire history. The 

increase can be attributed to accumulation of living and dead fuels coupled with extended 
10 

drought conditions. Another factor is the population boom of the past several decades as the 

urban-forest interface merges. Overall, the greatest threat is at higher elevation where fuels are 

more supportive of extreme fires. Figure 38, Figure 39 and Figure 40 show wildfire hazard 

severity and risk, notice that the greatest threat is at higher elevation, where fuels are more 

supportive of extreme fires. 

C. Snow and Ice 

Arizona winters are highly variable with regards to temperature and snowfall from one year to 

the next. The impact of any given Arizona winter is highly dependant on the type of storm 

track that becomes established. Ideally for wet winters, a track from the Pacific Ocean, south to 

San Diego and across the state develops. Cold, dry winters typically see a storm track along the 

western Rockies from the Great Basin southeast to New Mexico, although this track can also 

provide snowfall for northern Arizona. The variability in storm track and subsequent Arizona 

winters are influenced by ENSO patterns. El Nino is an abnormal warming of the equatorial 

Pacific Ocean waters and tends to strengthen the southern jet stream. This jet stream develops 

an orientation from the central Pacific eastward across Arizona. Pacific storm systems and 

associated moisture follow this track, bringing precipitation, often as heavy snowfall, to the 

state. Conversely, a La Nina pattern develops when there is abnormal cooling of the ocean 

waters near the equatorial Pacific. This leads to a northward shift of the jet stream with an 

orientation over the Northwest United States. Under this pattern Arizona is typically influenced 

by a ridge of high pressure which blocks moisture and incoming systems leading to warm 

wintertime temperatures. However, many winters are not easily classified as El Nino or La 

Nina and show high variability within the winter year itself. 

The main time period for winter weather in Arizona is from November through March, with 

the peak in January and February. The heaviest snow typically occurs along the Mogollon rim 

where yearly snowfall amounts in excess of 100 inches are common. Figure 41 and Figure 42 

shows the yearly snowfall across the state. Notice the extreme snowfall variability, with 

amounts from zero over the southwest part of the state to up to 200 inches over the Mogllon 

rim. Figure 43 and Figure 44 depict the mean annual snowfall days over the state, which 

further illustrates just how different winters are from one part of the state to the next. 

Cold temperatures are also quite common over the northern portion of the state and at 

elevations above 7000 feet in the southeast. In these locations low temperatures fall to well 

below zero. Exposure to the cold temperatures is a major contributor to the total fatalities 

statistics in the Heat/Cold hazardous weather category. Cold temperatures often act in unison 

with heavy snowfall events that can strand and isolate people, allowing exposure to the cold to 

take hold. This is especially the case for those engaged in outdoor activities from November 

through March. 

Travel in Arizona’s diverse terrain can also be hazardous during storms. Many highways that 

traverse the state see elevation changes of several thousand feet over a short distance. These 

changes in elevation can lead to rapid changes in visibility and deteriorating road conditions 

catching motorists off guard. Vehicle accidents during winter storms account for a large 

percentage of the fatalities that fall in the Snow/Ice hazardous weather category. Figure 45 

shows the snow and ice storm frequency by month over the state. 
11 

VII. Summary 

The results of this study can be summarized in the following: 

• The extremely low population density (45.2 people per sq mi) of much of Arizona has 

likely resulted in many hazardous weather events not being reported, especially those 

which occur away from population centers. Additionally, there is a significant bias to 

reports along roadways in rural areas. 

• The greatest weather hazard in Arizona is exposure to extreme temperatures (Extreme 

Heat/Cold category) which is responsible for the largest number of fatalities. The 

highest component is extreme heat and this is actually an even greater killer than the 

data depicts. 

• Arizona has an annual thunderstorm frequency comparable to many Plains States.

• Tornadoes are a more common occurrence in Arizona than most people are aware, 

primarily over the central valleys and plateau regions. For the state, the average 

number of reported tornadoes is approximately 4 per year.

• A high percentage of reported tornadoes in this state are weak, either F0 or F1. 

• Hail ranks only as the third most frequent hazardous weather type, but is still 

responsible for a considerable percentage of property and crop damage. The state 

averages 12 severe hail events per year. 

• Arizona averages 29 severe wind events per year, with the greatest concentration over 

the southern most climate regions. 

• Arizona thunderstorm wind events are mainly clustered over a two month period: July 

and August. 

• In Arizona, flooding ranks second to extreme heat in the number of reported fatalities. 

Arizona ranks tenth in the nation in flooding deaths per capita. The Southeast climate 

zone has a flash flood frequency nearly equal to all other zones combined for the 

months of July and August. 

• Dust storms are often underestimated as significant weather events and rank only 

behind extreme heat/cold and flooding for deaths and injuries. 

• Despite a relatively high flash density, Arizona ranks in the middle of the pack 

nationally for lightning casualties per capita. 
12 

• Dust devils in Arizona can have a surprisingly destructive side, with winds up to 70 

miles per hour. Dust devils are often cross-listed with dust storms making it hard to 

obtain accurate information on historically dust devil damage. 

• It is difficult to measure state drought effects in monetary or casualty form, since its 

effects are subtle, gradual, and often linked to some other hazardous event (heat and 

wildfires). 

• High impact wildfires have been far more common over the last decade than previous 

several decades.

• The main Arizona wintertime hazardous weather aspect is exposure to the cold 

temperatures and heavy snowfall over the higher terrain of northern and eastern parts 

of the State.

VIII. References 

Abbey, R. F., Jr., and Fujita, T. T., 1975. Use of tornado path lengths and gradations of damage 

to assess tornado intensity probabilities, in Preprints, 9th Conference on Severe Local 

Storms, Norman: American Meteorological Society, Boston, p. 286- 293. 

Adams, D.K. and A.C. Comrie, 1997: The North American Monsoon. Bull. Amer.Meteor. Soc., 

78, 2197–2213.

ADHS’ Division of Public Health Services: Injury Mortality among Arizona residents. 

[Available online at http://www.azdhs.gov/plan/report/im/imindex.html] 

Arizona State Land Department: Forestry Division. [Available online at 

http://www.azsf.az.gov/fire_managment/communities_at_risk/default.asp] 

Blanchard, D.O., 2000: Forecasting Severe Weather along the Mogollon Rim Convergence 

Zone. Preprints, 20th Conf. on Severe Local Storms, Orlando, Meteor. Soc., 563-566. 

______ ,2006: A Cool Season Severe Weather Episode in Northern Arizona. [Available online 

at http://ams.confex.com/ams/pdfpapers/115214.pdf] 

Brazel, A.J. and W.G. Nickling, 1986: The Relationship of Weather Types to Dust Storm 

Generation in Arizona (1965-1980). Journal of Climatology, 6, 255-275. 

CLIMAS Drought Planning and Mitigation. [Available online at 

http://www.ispe.arizona.edu/climas/research/drought/Figures/fig1.html] 

Climate Prediction Center (CPC). Composite Palmer Drought Severity Index 1950-1995 

[Available online at http://www.cpc.noaa.gov/products] 

Colorado Climate Center, Colorado State University. Mean annual snowfall for the United 

States for the period 1961-1990. Mean number of days per year with one inch or more 

of snow on the ground for the period 1961-1990. [Available online at 

http://ccc.atmos.colostate.edu/snowbooklet.php#Snmaps] 

Corbosiero, K. L., The Contribution of Eastern North Pacific Tropical Cyclones to the Warm 

Season Rainfall Climatology of the Southwest United State [Available online at 

http://www.atmos.ucla.edu/~kristen/monsoon/monsoon.html] 

Curran, E.B., R.L. Holle, and R.E. López, 2000: Lightning Casualties and Damages in the 

United States from 1959 to 1994. Journal of Climate, 13, 3448-3453. 
13 

FEMA: Arizona Disaster History. [Available online at 

http://www.fema.gov/news/disasters_state.fema?id=4] 

Hsin-mu Lin, Pao K. Wang and Robert E. Schlesinger, Three-dimensional nonhydrostatic 

simulations of summer thunderstorms in the humid subtropics versus High Plains, 

Atmospheric ResearchVolume 78, Issues 1-2, , November 2005, Pages 103-145. 

Keim, S.M., M.Z. Mays, B. Parks, E. Pytlak, R.M. Harris, and M.A. Kent, 2006: Estimating 

the Incidence of Hear-Related Deaths among Immigrants in Pima County, Arizona. J. 

of Immigrants and Minority Health, 8, No. 2, 185-191. 

National Drought Mitigation Center. National Palmer Drought Severity Index (1895-1995) 

[Available online at http://www.drought.unl.edu/whatis/palmer/pdsihist.htm] 

National Oceanic and Atmospheric Administration, 1959-2004: Storm Data. National Climatic 

Data Center, Asheville, NC, 1-40, Nos. 1-12. 

NCDC’s Storm Events Database. [Available online at http://www4.ncdc.noaa.gov/cgiwin/wwcgi.dll?wwEvent~Storms] 

NHTSA’s Fatality Analysis Reporting System (FARS). [Available online at http://www.-

fars.nhtsa.dot.gov] 

NWS’ Storm Prediction Center Database. [Available online at http://www.spc.noaa.gov/wcm] 

Oklahoma Climatological Survey. Map of average number of thunderstorm days in U.S. 

[Available online at http://www.ocs.ou.edu] 

Paulson, R.W., E.B. Chase, R.S. Roberts, and D.W. Moody, compilers, 1991: National Water 

Summary 1988-89: Hydrologic Events and Floods and Droughts. U.S. Geological 

Survey Water-Supply, Paper 2375, 591. 

Redmond, K.T., 2002: The Depiction of Drought: A Commentary. Bull. Amer. Meteor. Soc, 

83, 1143–1147.

Renno, N. O., M. L. Burkett, and M. P. Larkin, A simple thermodynamical theory for dust 

devils, J. Atmos. Sci., 55, 3244– 3252, 1998. 

Sellers, W.D., and R.H. Hill, 1974: Arizona Climate (1931-1972). University of Arizona Press. 

_____, R.H. Hill, and M. Sanderson-Rae, 1985: Arizona Climate: The first Hundred Years 

(1885-1985). Tucson, University of Arizona. 

University of Arizona’s College of Agriculture Arizona Storm Database. [Available online at 

http://ag2.calsnet.arizona.edu/egi-bin/storms.egi] 

United States Census Bureau, 2000: [Available online at http://www.census.gov] 

Vaisala NLDN.(Vaisala). Vaisala’s Ten year flash density for the U.S. from 1996-2005. Rate 

of lightning fatalities per population ordered by state from 1997 to 2006 [Available 

online at http://www.vaisala.com] 

Watson, A.I., R.L. Holle, and R.E. Lopez, 1994: Diurnal cloud-to-ground lightning patterns in 

Arizona during the southwest monsoon. Mon. Wea. Rev., 122, 1716-1725. 
14 

Figure 1. Example of Storm Data, historical, and spotter reports skewed toward cities and major 

highways for wind events. 
15 

Figure 2. Example of the Storm Data discrepancy for the Labor Day weekend storm in 

Arizona. No deaths were reported in the publication even though 23 deaths occurred during 

this statewide flash flood and flood event. 
16 

Arizona Climate Regions Arizona Climate Regions 

from Sellers and Hill (1974) from Sellers and Hill (1974)

Northeast

Southwest

Southeast

Northwest

Central

Plateau

Figure 3. Arizona climate regions used in this study as defined by Sellers and Hill 

(1974). 
17 

AZ Fatalities and Injuries By Hazard

Storm Data 1955-2004

0

100

200

300

400

500

600

Fatalities

Injuries

Hail Tornado Wind Snow/

Ice

Dust

Storm

Lightning Extreme Flood

Heat/Cold

*

*AZ Injury Mortality Report 1990-2000 

Arizona Deaths and Injuries Arizona Deaths and Injuries

by Hazardous Weather Type by Hazardous Weather Type

1955-2004

Data Sources: •Arizona Climate- The First Hundred Years (Sellers, Hill and Sanderson-Rae)

•NCDC Storm Data 1955-2004

•SPC Events Database 1950-2004

•NCDC Storm Events Database: Online- www4.ncdc.noaa.gov/cgi-win/wwcgi.dll?wwEvent~Storms

•DOT Fatality Analysis Reporting System: Online- www-fars.nhtsa.dot.gov

•University of Arizona Storm Database: Online- ag2.calsnet.arizona.edu/cgi-bin/storms.cgi

•Injury Mortality Among Arizona Residents, 1990-2000 Report (March 2002)

Figure 4. Injures and fatalities in Arizona sub-divided by weather event for the period 

of 1955 to 2004 
18 

Arizona Tornadoes Arizona Tornadoes

1950-2004

Arizona Averages 4 Tornadoes per Year

Number of Tornadoes Reported By County

20

13

14

19

57

12 17

10

0

25 0

0

3

6

Apache: 6

Cochise: 12

Coconino: 20

Gila: 3

Graham: 0

Greenlee: 0

La Paz: 0

Mohave: 14

Maricopa: 57

Navajo: 13

Pima: 17

Pinal: 25

Santa Cruz: 0

Yavapai: 19

Yuma: 10 0

Figure 5. Total tornadoes in each county from 1950 to 2004 

Little Colorado

River Valley

Mogollon Rim

Mogollon Rim Convergence 

Zone (MRCZ)

Mogollon Mogollon Rim Convergence Zone (MRCZ) Rim Convergence Zone (MRCZ)

A region of non A region of non-supercell supercell tornadoes tornadoes

Blanchard (2000) Blanchard (2000)

Figure 6. Mogollon Rim Convergence Zone (MRCZ) noted by Blanchard (2000) 
19 

AZ Tornadoes By F Scale

Storm Data 1950-2004

0

20

40

60

80

100

Unknown F0 F1 F2 F3

Figure 7. Tornado frequency by F scale from 1950 to 2004 

AZ Tornadoes By Month and F Scale

Storm Data 1950-2004

0

5

10

15

20

25

1 2 3 4 5 6 7 8 9 10 11 12

Month

Unknown

F0

F1

F2

F3

Figure 8. Tornado frequency by month and F scale from 1950 to 2004 
20 

AZ Tornadoes By Month

Storm Data 1950-2004

0

10

20

30

40

50

1 2 3 4 5 6 7 8 9 10 11 12

Month

Event

s

Events

Figure 9. Tornado frequency by month from 1950 to 2004 

NW AZ Tornadoes By Month

Storm Data 1950-2004

0

2

4

6

8

10

Jan

Feb

Mar

Apr

May

Jun

Jul

Aug

Sep

Oct

Nov

Dec

Month

SW AZ Tornadoes By Month

Storm Data 1950-2004

0

2

4

6

8

10

12

14

16

Jan

Feb

MarApr

May

Jun

Jul

Aug

Sep

Oct

Nov

Dec

Month

SE AZ Tornadoes By Month

Storm Data 1950-2004

0

2

4

6

8

10

12

Jan

Feb

Mar

Apr

May

Jun

Jul

Aug

Sep

Oct

Nov

Dec

Month

NE AZ Tornadoes By Month

Storm Data 1950-2004

0

1

2

3

4

5

6

7

Jan

Feb

Mar

Apr

May

Jun

Jul

Aug

Sep

Oct

Nov

Dec

Month

Plateau AZ Tornadoes By Month

1950-2004

0

1

2

3

4

5

6

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

Events

Arizona Tornadoes Arizona Tornadoes 

Frequency by Month and Region Frequency by Month and Region

1950-2004

Central AZ Tornadoes By Month

1950-2004

0

1

2

3

4

5

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

Events

Figure 10. Tornado frequency by month and climate region from 1950 to 2004 
21 

Figure 11. Tornado frequency by hour (Time MST) from 1950 to 2004 

AZ Tornadoes By Time

1950-2004

0

5

10

15

20

25

30

1 3 5 7 9 11 13 15 17 19 21 23

Time (MST)
22 

Arizona Tornadoes Arizona Tornadoes 

by Month and Region by Month and Region 

1950-2004

SW AZ Tornadoes By Month

Storm Data 1950-2004

0

2

4

6

8

10

12

14

16

Jan

Feb

Mar

Apr

May

Jun

Jul

Aug

Sep

Oct

Nov

Dec

Month Four Corner Region Tornadoes By Month

Storm Data 1950-2004

0

2

4

6

8

10

Jan

Feb

Mar

Apr

May

Jun

Jul

Aug

Sep

Oct

Nov

Dec

Month

NE AZ Tornadoes By Month

Storm Data 1950-2004

0

1

2

3

4

5

6

7

Jan

Feb

Mar

Apr

May

Jun

Jul

Aug

Sep

Oct

Nov

Dec

Month

Peak JUL thru SEP

Possible Peak

JAN thru MAR

SEP thru OCT

APR thru JUN

SW Arizona

NE Arizona *Although Rare Events

Four Corners

Figure 12. Secondary peak in the annual tornado frequency for the Southwest and 

Northeast climate regions from 1950 to 2004. The frequency for the four corners region 

of the United States is included for comparison with the Arizona Northeast climate 

region. 
23 

Arizona Hail Arizona Hail

1955-2004

Percentage of Hail Events By County

15% 2%

8%

7%

14%

15% 2%

1%

4%

16%

16%

2%

1%

6%

Arizona Averages 12 Hail Events per Year

1%

Figure 13. The percentage of hail events by County from 1955 to 2004 

0

20

40

60

80

100

120

140

Events

1 2 3 4 5 6 7 8 9 10 11 12

Month

AZ Hail Events By Month and Size

Storm Data 1955-2004

.75-1.50 in

>1.50 in

Figure 14. Hail frequency by month and size from 1955 to 2004 
24 

AZ Hail Events By Hour

Storm Data 1955-2004

0

10

20

30

40

50

60

70

80

1 3 5 7 9 11 13 15 17 19 21 23

Hour (MST)

Event

s

Events

Figure 15. Hail frequency of hour from 1955 to 2004 

Arizona Thunderstorm Wind Arizona Thunderstorm Wind 

1955-2004

Total Number of Reported Events by Region

40

803

396

99

18 76

Arizona Averages 29 Thunderstorm Wind Events per Year

Most Frequent

in Southwest &

Southeast

Figure 16. Thunderstorm wind events by climate region from 1955 to 2004 
25 

AZ Thunderstorm Wind Events By Month

Storm Data 1955-2004

0

100

200

300

400

500

600

700

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

Events

Figure 17. Thunderstorm wind frequency by month from 1955 to 2004 

AZ Thunderstorm Wind Events By Hour

Storm Data 1955-2004 

0

50

100

150

200

250

300

1 3 5 7 9 11 13 15 17 19 21 23

Hour (MST)

Events

Figure 18. Thunderstorm wind frequency by hour from 1955 to 2004 
26 

Southeast Thunderstorm Events By Hour

Storm Data 1955-2004

0

10

20

30

40

50

60

70

80

1 3 5 7 9 11 13 15 17 19 21 23

Hour (MST)

Events

Events

Southwest Thunderstorm Wind Events By Hour

Storm Data 1955-2004

0

20

40

60

80

100

120

140

160

1 3 5 7 9 11 13 15 17 19 21 23

Hour (MST)

Events

Events

Arizona Thunderstorm Wind Arizona Thunderstorm Wind

Frequency by Hour and Region Frequency by Hour and Region

1955-2004

Central Thunderstorm Wind Events By Hour

Storm Data 1955-2004

0

5

10

15

20

1 3 5 7 9 11 13 15 17 19 21 23

Hour (MST)

Events

Events

Northeast Thunderstorm Wind Events By Hour

Storm Data 1955-2004

0

2

4

6

8

10

1 3 5 7 9 11 13 15 17 19 21 23

Hour (MST)

Events

Events

Plateau Thunderstorm Wind Events By Hour

Storm Data 1955-2004

0

1

2

3

4

5

1 3 5 7 9 11 13 15 17 19 21 23

Hour (MST)

Events

Events

Northwest Thunderstorm Wind Events By Hour

Storm Data 1955-2004

0

5

10

15

20

1 3 5 7 9 11 13 15 17 19 21 23

Hour (MST)

Events

Events

Southwest events 

tend to peak later in

the day

Figure 19. Thunderstorm wind frequency by hour and climate region from 1955 to 2004 

AZ Flash Flood & Flood Events By 

Month

Storm Data 1955-2004

0

50

100

150

200

250

300

350

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

Events

Figure 20. Flash flood and flood frequency by month from 1955 to 2004 
27 

AZ Flash Flood & Flood Events By Hour

1955 to 2004

0

10

20

30

40

50

60

70

1 3 5 7 9 11 13 15 17 19 21 23

Events

Figure 21. Flash flood and flood frequency by hour from 1955 to 2004 

Arizona Flash Flood/Flood

Frequency by Month and Region Frequency by Month and Region

1955-2004

Plateau Flash Flood & Flood Events By

Month

Storm Data 1955 to 2004

0

5

10

15

20

25

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

Events

Northeast Flash Flood & Flood Events By

Month

Storm Data 1955 to 2004

0

2

4

6

8

10

12

14

16

18

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

Events

Central Flash Flood & Flood Events By

Month

Storm Data 1955 to 2004

0

5

10

15

20

25

30

35

40

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

Events

Southwest Flash Flood & Flood 

By Month

Storm Data 1955 to 2004

0

10

20

30

40

50

60

70

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

Events

Southeast Flash Flood & Flood Events 

By Month

Storm Data 1955 to 2004

0

20

40

60

80

100

120

140

160

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

Events

Northwest Flash Flood & Flood Events By

Month

Storm Data 1955 to 2004

0

5

10

15

20

25

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

Events

Figure 22. Flash flood and flood frequency by month and climate region from 1955 to 2004 
28 

Figure 23. Areal extent of some historical floods in Arizona (U.S Geological Survey) 

Figure 24. Tropical system tracks over the Pacific and southwest U.S. 1958-2003. Red 

denotes tracks over the southwest states, black are tracks over the Pacific and 

dissipation over Mexico. (Corbosiero) 
29 

AZ Dust Storm/Blowing Dust Fatalities 

By Month

0

5

10

15

20

25

1 2 3 4 5 6 7 8 9 10 11 12

Month

Fatalities

Events

Figure 25. Frequency of dust storm fatalities by month from 1955 to 2004 

Figure 26. Average number of thunderstorm days (Oklahoma Climatological Survey)
30 

Figure 27. The ten year flash density for the U.S from 1996-2005 (Vaisala Inc.) 

AZ Lightning Fatalities and Injures By Month

1955 - 2004

0

10

20

30

40

50

60

1 2 3 4 5 6 7 8 9 10 11 12

Month

Count

Fatalities

Injuries

Figure 28. Lightning Fatalities and Injuries by month from 1955 to 2004 
31 

Figure 29. Rate of lightning casualties (deaths and injuries combined) per population 

ordered by state from 1959 to 1994 (Curran, et. al, 2000) 
32 

Figure 30. Rate of lightning fatalities per population ordered by state from 1997 to 2006. 

Data and image provided courtesy of Vaisala NLDN (Vaisala Inc.) 
33 

Figure 31. A close up of the ten year flash density for Arizona from 1996-2005 (Vaisala Inc.) 

Figure 32. Flash density key (Vaisala Inc.) 
34 

Figure 33. Flash densities (flashes per 100 km2 per monsoon season) for 20 km x 20 km 

boxes during all hours for 1985-1990 (Watson, et. al 1993). 
35 

Figure 34. National Palmer Drought Severity Index (1895-1995) 

(National Drought Mitigation Center) 

Figure 35. Drought Extent, Length and Composite Palmer Drought Severity Indexes 

for Arizona (1950-1995) (Climate Prediction Center) 
36 

Figure 36. Areal extent of some historical droughts in Arizona (Paulson, et al.) 

Figure 37. Arizona statewide water year precipitation, 1896-2005 (CLIMAS). 

Red highlights time periods of low precipitation.
37 

Figure 38. Wildfire Hazard Areas Map (Arizona State Land Department: Forestry Division)
38 

Figure 39. Fire Hazard is based upon factors such as fuel types and condition, natural fire 

regimes, and topography and the influence of structures. 

(Arizona State Land Department: Forestry Division) 

Figure 40. Fire hazard key (Arizona State Land Department: Forestry Division) 
39 

Figure 41. Mean annual snowfall for Arizona for the period 1961-1990 

(Colorado Climate Center) 

Figure 42. Key for mean annual snowfall for Arizona for the period 1961-1990 

(Colorado Climate Center) 
40 

Figure 43. Mean annual snowfall days for Arizona for the period 1961-1990 

(Colorado Climate Center) 

Figure 44. Key for mean annual snowfall days for Arizona for the period 1961-1990 

(Colorado Climate Center) 
41 

Snow/Ice by Month

1955-2004

0

5

10

15

20

25

30

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

Month

Events

Figure 45. Snow and Ice by month from 1955 to 2004
42 

NOAA TECHNICAL MEMORANDA 

National Weather Service, Western Region 

Subseries

The National Weather Service (NWS) Western Region (WR) Subseries 

provides an informal medium for the documentation and quick 

dissemination of results not appropriate, or not yet ready, for formal 

publication. The series is used to report on work in progress, to describe 

technical procedures and practices, or to relate progress to a limited 

audience. These Technical Memoranda will report on investigations 

devoted primarily to regional and local problems of interest mainly to 

personnel, and hence will not be widely distributed. 

Papers 1 to 25 are in the former series, ESSA Technical Memoranda, 

Western Region Technical Memoranda (WRTM); papers 24 to 59 are in the 

former series, ESSA Technical Memoranda, Weather Bureau Technical 

Memoranda (WBTM). Beginning with 60, the papers are part of the series, 

NOAA Technical Memoranda NWS. Out-of-print memoranda are not listed. 

Papers 2 to 22, except for 5 (revised edition), are available from the 

National Weather Service Western Region, Scientific Services Division, 125 

South State Street - Rm 1311, Salt Lake City, Utah 84138-1102. Paper 5 

(revised edition), and all others beginning with 25 are available from the 

National Technical Information Service, U.S. Department of Commerce, 

Sills Building, 5285 Port Royal Road, Springfield, Virginia 22161. Prices 

vary for all paper copies; microfiche are $3.50. Order by accession number 

shown in parentheses at end of each entry. 

ESSA Technical Memoranda (WRTM)

2 Climatological Precipitation Probabilities. Compiled by Lucianne 

Miller, December 1965. 

3 Western Region Pre- and Post-FP-3 Program, December 1, 1965, to 

February 20, 1966. Edward D. Diemer, March 1966. 

5 Station Descriptions of Local Effects on Synoptic Weather Patterns. 

Philip Williams, Jr., April 1966 (Revised November 1967, October 

1969). (PB-17800) 

8 Interpreting the RAREP. Herbert P. Benner, May 1966 (Revised 

January 1967). 

11 Some Electrical Processes in the Atmosphere. J. Latham, June 1966. 

17 A Digitalized Summary of Radar Echoes within 100 Miles of 

Sacramento, California. J. A. Youngberg and L. B. Overaas, 

December 1966. 

21 An Objective Aid for Forecasting the End of East Winds in the 

Columbia Gorge, July through October. D. John Coparanis, April 

1967. 

22 Derivation of Radar Horizons in Mountainous Terrain. Roger G. 

Pappas, April 1967. 

ESSA Technical Memoranda, Weather Bureau Technical Memoranda 

(WBTM) 

25 Verification of Operation Probability of Precipitation Forecasts, April 

1966-March 1967. W. W. Dickey, October 1967. (PB-176240) 

26 A Study of Winds in the Lake Mead Recreation Area. R. P. Augulis, 

January 1968. (PB-177830) 

28 Weather Extremes. R. J. Schmidli, April 1968 (Revised March 1986). 

(PB86 177672/AS). (Revised October 1991 - PB92-115062/AS) 

29 Small-Scale Analysis and Prediction. Philip Williams, Jr., May 1968. 

(PB178425) 

30 Numerical Weather Prediction and Synoptic Meteorology. CPT 

Thomas D. Murphy, USAF, May 1968. (AD 673365) 

31 Precipitation Detection Probabilities by Salt Lake ARTC Radars. 

Robert K. Belesky, July 1968. (PB 179084) 

32 Probability Forecasting--A Problem Analysis with Reference to the 

Portland Fire Weather District. Harold S. Ayer, July 1968. (PB 

179289) 

36 Temperature Trends in Sacramento--Another Heat Island. Anthony D. 

Lentini, February 1969. (PB 183055) 

37 Disposal of Logging Residues Without Damage to Air Quality. Owen 

P. Cramer, March 1969. (PB 183057) 

39 Upper-Air Lows Over Northwestern United States. A.L. Jacobson, 

April 1969. PB 184296) 

40 The Man-Machine Mix in Applied Weather Forecasting in the 1970s. 

L.W. Snellman, August 1969. (PB 185068) 

43 Forecasting Maximum Temperatures at Helena, Montana. David E. 

Olsen, October 1969. (PB 185762) 

44 Estimated Return Periods for Short-Duration Precipitation in Arizona. 

Paul C. Kangieser, October 1969. (PB 187763) 

46 Applications of the Net Radiometer to Short-Range Fog and Stratus 

Forecasting at Eugene, Oregon. L. Yee and E. Bates, December 

1969. (PB 190476) 

47 Statistical Analysis as a Flood Routing Tool. Robert J.C. Burnash, 

December 1969. (PB 188744) 

48 Tsunami. Richard P. Augulis, February 1970. (PB 190157) 

49 Predicting Precipitation Type. Robert J.C. Burnash and Floyd E. Hug, 

March 1970. (PB 190962) 

50 Statistical Report on Aeroallergens (Pollens and Molds) Fort 

Huachuca, Arizona, 1969. Wayne S. Johnson, April 1970. (PB 

191743) 

51 Western Region Sea State and Surf Forecaster's Manual. Gordon C. 

Shields and Gerald B. Burdwell, July 1970. (PB 193102) 

52 Sacramento Weather Radar Climatology. R.G. Pappas and C. M. 

Veliquette, July 1970. (PB 193347) 

54 A Refinement of the Vorticity Field to Delineate Areas of Significant 

Precipitation. Barry B. Aronovitch, August 1970. 

55 Application of the SSARR Model to a Basin without Discharge Record. 

Vail Schermerhorn and Donal W. Kuehl, August 1970. (PB 194394) 

56 Areal Coverage of Precipitation in Northwestern Utah. Philip Williams, 

Jr., and Werner J. Heck, September 1970. (PB 194389) 

57 Preliminary Report on Agricultural Field Burning vs. Atmospheric 

Visibility in the Willamette Valley of Oregon. Earl M. Bates and David 

O. Chilcote, September 1970. (PB 194710) 

58 Air Pollution by Jet Aircraft at Seattle-Tacoma Airport. Wallace R. 

Donaldson, October 1970. (COM 71 00017) 

59 Application of PE Model Forecast Parameters to Local-Area 

Forecasting. Leonard W. Snellman, October 1970. (COM 71 00016) 

60 An Aid for Forecasting the Minimum Temperature at Medford, Oregon, 

Arthur W. Fritz, October 1970. (COM 71 00120) 

63 700-mb Warm Air Advection as a Forecasting Tool for Montana and 

Northern Idaho. Norris E. Woerner, February 1971. (COM 71 00349) 

64 Wind and Weather Regimes at Great Falls, Montana. Warren B. 

Price, March 1971. 

65 Climate of Sacramento, California. Laura Masters-Bevan. NWSO 

Sacramento, November 1998 (6th Revision. (PB99-118424) 

66 A Preliminary Report on Correlation of ARTCC Radar Echoes and 

Precipitation. Wilbur K. Hall, June 1971. (COM 71 00829) 

69 National Weather Service Support to Soaring Activities. Ellis Burton, 

August 1971. (COM 71 00956) 

71 Western Region Synoptic Analysis-Problems and Methods. Philip 

Williams, Jr., February 1972. (COM 72 10433) 

74 Thunderstorms and Hail Days Probabilities in Nevada. Clarence M. 

Sakamoto, April 1972. (COM 72 10554) 

75 A Study of the Low Level Jet Stream of the San Joaquin Valley. 

Ronald A. Willis and Philip Williams, Jr., May 1972. (COM 72 10707) 

76 Monthly Climatological Charts of the Behavior of Fog and Low Stratus 

at Los Angeles International Airport. Donald M. Gales, July 1972. 

(COM 72 11140) 

77 A Study of Radar Echo Distribution in Arizona During July and August. 

John E. Hales, Jr., July 1972. (COM 72 11136) 

78 Forecasting Precipitation at Bakersfield, California, Using Pressure 

Gradient Vectors. Earl T. Riddiough, July 1972. (COM 72 11146) 

79 Climate of Stockton, California. Robert C. Nelson, July 1972. (COM 

72 10920) 

80 Estimation of Number of Days Above or Below Selected 

Temperatures. Clarence M. Sakamoto, October 1972. (COM 72 

10021) 

81 An Aid for Forecasting Summer Maximum Temperatures at Seattle, 

Washington. Edgar G. Johnson, November 1972. (COM 73 10150) 

82 Flash Flood Forecasting and Warning Program in the Western 

Region. Philip Williams, Jr., Chester L. Glenn, and Roland L. Raetz, 

December 1972, (Revised March 1978). (COM 73 10251) 

83 A comparison of Manual and Semiautomatic Methods of Digitizing 

Analog Wind Records. Glenn E. Rasch, March 1973. (COM 73 

10669) 

86 Conditional Probabilities for Sequences of Wet Days at Phoenix, 

Arizona. Paul C. Kangieser, June 1973. (COM 73 11264) 

87 A Refinement of the Use of K-Values in Forecasting Thunderstorms in 

Washington and Oregon. Robert Y.G. Lee, June 1973. (COM 73 

11276) 

89 Objective Forecast Precipitation Over the Western Region of the 

United States. Julia N. Paegle and Larry P. Kierulff, September 1973. 

(COM 73 11946/3AS) 

91 Arizona "Eddy" Tornadoes. Robert S. Ingram, October 1973. (COM 

73 10465) 

92 Smoke Management in the Willamette Valley. Earl M. Bates, May 

1974. (COM 74 11277/AS) 

93 An Operational Evaluation of 500-mb Type Regression Equations. 

Alexander E. MacDonald, June 1974. (COM 74 11407/AS) 

94 Conditional Probability of Visibility Less than One-Half Mile in 

Radiation Fog at Fresno, California. John D. Thomas, August 1974. 

(COM 74 11555/AS) 

95 Climate of Flagstaff, Arizona. Paul W. Sorenson, and updated by 

Reginald W. Preston, January 1987. (PB87 143160/AS) (Revised 

August 2002 3rd Revision) 

96 Map type Precipitation Probabilities for the Western Region. Glenn E. 

Rasch and Alexander E. MacDonald, February 1975. (COM 75 

10428/AS) 

97 Eastern Pacific Cut-Off Low of April 21-28, 1974. William J. Alder and 

George R. Miller, January 1976. (PB 250 711/AS) 

98 Study on a Significant Precipitation Episode in Western United States. 

Ira S. Brenner, April 1976. (COM 75 10719/AS) 

99 A Study of Flash Flood Susceptibility-A Basin in Southern Arizona. 

Gerald Williams, August 1975. (COM 75 11360/AS) 

102 A Set of Rules for Forecasting Temperatures in Napa and Sonoma 

Counties. Wesley L. Tuft, October 1975. (PB 246 902/AS) 

103 Application of the National Weather Service Flash-Flood Program in 

the Western Region. Gerald Williams, January 1976. (PB 253 

053/AS) 

104 Objective Aids for Forecasting Minimum Temperatures at Reno, 

Nevada, During the Summer Months. Christopher D. Hill, January 

1976. (PB 252 866/AS) 

105 Forecasting the Mono Wind. Charles P. Ruscha, Jr., February 1976. 

(PB 254 650) 
43 

106 Use of MOS Forecast Parameters in Temperature Forecasting. John 

C. Plankinton, Jr., March 1976. (PB 254 649) 

107 Map Types as Aids in Using MOS PoPs in Western United States. Ira 

S. Brenner, August 1976. (PB 259 594) 

108 Other Kinds of Wind Shear. Christopher D. Hill, August 1976. (PB 

260 437/AS) 

109 Forecasting North Winds in the Upper Sacramento Valley and 

Adjoining Forests. Christopher E. Fontana, September 1976. (PB 

273 677/AS) 

110 Cool Inflow as a Weakening Influence on Eastern Pacific Tropical 

Cyclones. William J. Denney, November 1976. (PB 264 655/AS) 

112 The MAN/MOS Program. Alexander E. MacDonald, February 1977. 

(PB 265 941/AS) 

113 Winter Season Minimum Temperature Formula for Bakersfield, 

California, Using Multiple Regression. Michael J. Oard, February 

1977. (PB 273 694/AS) 

114 Tropical Cyclone Kathleen. James R. Fors, February 1977. (PB 273 

676/AS) 

116 A Study of Wind Gusts on Lake Mead. Bradley Colman, April 1977. 

(PB 268 847) 

117 The Relative Frequency of Cumulonimbus Clouds at the Nevada Test 

Site as a Function of K-Value. R.F. Quiring, April 1977. (PB 272 831) 

118 Moisture Distribution Modification by Upward Vertical Motion. Ira S. 

Brenner, April 1977. (PB 268 740) 

119 Relative Frequency of Occurrence of Warm Season Echo Activity as a 

Function of Stability Indices Computed from the Yucca Flat, Nevada, 

Rawinsonde. Darryl Randerson, June 1977. (PB 271 290/AS) 

121 Climatological Prediction of Cumulonimbus Clouds in the Vicinity of 

the Yucca Flat Weather Station. R.F. Quiring, June 1977. (PB 271 

704/AS) 

122 A Method for Transforming Temperature Distribution to Normality. 

Morris S. Webb, Jr., June 1977. (PB 271 742/AS) 

124 Statistical Guidance for Prediction of Eastern North Pacific Tropical 

Cyclone Motion - Part I. Charles J. Neumann and Preston W. 

Leftwich, August 1977. (PB 272 661) 

125 Statistical Guidance on the Prediction of Eastern North Pacific 

Tropical Cyclone Motion - Part II. Preston W. Leftwich and Charles J. 

Neumann, August 1977. (PB 273 155/AS) 

126 Climate of San Francisco. E. Jan Null, February 1978. (Revised by 

George T. Pericht, April 1988 and January 1995). (PB88 208624/AS) 

127 Development of a Probability Equation for Winter-Type Precipitation 

Patterns in Great Falls, Montana. Kenneth B. Mielke, February 1978. 

(PB 281 387/AS) 

128 Hand Calculator Program to Compute Parcel Thermal Dynamics. Dan 

Gudgel, April 1978. (PB 283 080/AS) 

129 Fire whirls. David W. Goens, May 1978. (PB 283 866/AS) 

130 Flash-Flood Procedure. Ralph C. Hatch and Gerald Williams, May 

1978. (PB 286 014/AS) 

131 Automated Fire-Weather Forecasts. Mark A. Mollner and David E. 

Olsen, September 1978. (PB 289 916/AS) 

132 Estimates of the Effects of Terrain Blocking on the Los Angeles WSR74C Weather Radar. R.G. Pappas, R.Y. Lee, B.W. Finke, October 

1978. (PB 289767/AS) 

133 Spectral Techniques in Ocean Wave Forecasting. John A. Jannuzzi, 

October 1978. (PB291317/AS) 

134 Solar Radiation. John A. Jannuzzi, November 1978. (PB291195/AS) 

135 Application of a Spectrum Analyzer in Forecasting Ocean Swell in 

Southern California Coastal Waters. Lawrence P. Kierulff, January 

1979. (PB292716/AS) 

136 Basic Hydrologic Principles. Thomas L. Dietrich, January 1979. 

(PB292247/AS) 

137 LFM 24-Hour Prediction of Eastern Pacific Cyclones Refined by 

Satellite Images. John R. Zimmerman and Charles P. Ruscha, Jr., 

January 1979. (PB294324/AS) 

138 A Simple Analysis/Diagnosis System for Real Time Evaluation of 

Vertical Motion. Scott Heflick and James R. Fors, February 1979. 

(PB294216/AS) 

139 Aids for Forecasting Minimum Temperature in the Wenatchee Frost 

District. Robert S. Robinson, April 1979. (PB298339/AS) 

140 Influence of Cloudiness on Summertime Temperatures in the Eastern 

Washington Fire Weather district. James Holcomb, April 1979. 

(PB298674/AS) 

141 Comparison of LFM and MFM Precipitation Guidance for Nevada 

During Doreen. Christopher Hill, April 1979. (PB298613/AS) 

142 The Usefulness of Data from Mountaintop Fire Lookout Stations in 

Determining Atmospheric Stability. Jonathan W. Corey, April 1979. 

(PB298899/AS) 

143 The Depth of the Marine Layer at San Diego as Related to 

Subsequent Cool Season Precipitation Episodes in Arizona. Ira S. 

Brenner, May 1979. (PB298817/AS) 

144 Arizona Cool Season Climatological Surface Wind and Pressure 

Gradient Study. Ira S. Brenner, May 1979. (PB298900/AS) 

146 The BART Experiment. Morris S. Webb, October 1979. (PB80 

155112) 

147 Occurrence and Distribution of Flash Floods in the Western Region. 

Thomas L. Dietrich, December 1979. (PB80 160344) 

149 Misinterpretations of Precipitation Probability Forecasts. Allan H. 

Murphy, Sarah Lichtenstein, Baruch Fischhoff, and Robert L. Winkler, 

February 1980. (PB80 174576) 

150 Annual Data and Verification Tabulation - Eastern and Central North 

Pacific Tropical Storms and Hurricanes 1979. Emil B. Gunther and 

Staff, EPHC, April 1980. (PB80 220486) 

151 NMC Model Performance in the Northeast Pacific. James E. 

Overland, PMEL-ERL, April 1980. (PB80 196033) 

152 Climate of Salt Lake City, Utah. William J. Alder, Sean T. Buchanan, 

William Cope (Retired), James A. Cisco, Craig C. Schmidt, Alexander 

R. Smith (Retired), Wilbur E. Figgins (Retired), February 1998 - 

Seventh Revision (PB98-130727) 

153 An Automatic Lightning Detection System in Northern California. 

James E. Rea and Chris E. Fontana, June 1980. (PB80 225592) 

154 Regression Equation for the Peak Wind Gust 6 to 12 Hours in 

Advance at Great Falls During Strong Downslope Wind Storms. 

Michael J. Oard, July 1980. (PB91 108367) 

155 A Raininess Index for the Arizona Monsoon. John H. Ten Harkel, July 

1980. (PB81 106494) 

156 The Effects of Terrain Distribution on Summer Thunderstorm Activity 

at Reno, Nevada. Christopher Dean Hill, July 1980. (PB81 102501) 

157 An Operational Evaluation of the Scofield/Oliver Technique for 

Estimating Precipitation Rates from Satellite Imagery. Richard Ochoa, 

August 1980. (PB81 108227) 

158 Hydrology Practicum. Thomas Dietrich, September 1980. (PB81 

134033) 

159 Tropical Cyclone Effects on California. Arnold Court, October 1980. 

(PB81 133779) 

160 Eastern North Pacific Tropical Cyclone Occurrences During 

Intraseasonal Periods. Preston W. Leftwich and Gail M. Brown, 

February 1981. (PB81 205494) 

161 Solar Radiation as a Sole Source of Energy for Photovoltaics in Las 

Vegas, Nevada, for July and December. Darryl Randerson, April 

1981. (PB81 224503) 

162 A Systems Approach to Real-Time Runoff Analysis with a 

Deterministic Rainfall-Runoff Model. Robert J.C. Burnash and R. 

Larry Ferral, April 1981. (PB81 224495) 

163 A Comparison of Two Methods for Forecasting Thunderstorms at 

Luke Air Force Base, Arizona. LTC Keith R. Cooley, April 1981. 

(PB81 225393) 

164 An Objective Aid for Forecasting Afternoon Relative Humidity Along 

the Washington Cascade East Slopes. Robert S. Robinson, April 

1981. (PB81 23078) 

165 Annual Data and Verification Tabulation, Eastern North Pacific 

Tropical Storms and Hurricanes 1980. Emil B. Gunther and Staff, May 

1981. (PB82 230336) 

166 Preliminary Estimates of Wind Power Potential at the Nevada Test 

Site. Howard G. Booth, June 1981. (PB82 127036) 

167 ARAP User's Guide. Mark Mathewson, July 1981, Revised 

September 1981. (PB82 196783) 

168 Forecasting the Onset of Coastal Gales Off Washington-Oregon. 

John R. Zimmerman and William D. Burton, August 1981. (PB82 

127051) 

169 A Statistical-Dynamical Model for Prediction of Tropical Cyclone 

Motion in the Eastern North Pacific Ocean. Preston W. Leftwich, Jr., 

October 1981. (PB82195298) 

170 An Enhanced Plotter for Surface Airways Observations. Andrew J. 

Spry and Jeffrey L. Anderson, October 1981. (PB82 153883) 

171 Verification of 72-Hour 500-MB Map-Type Predictions. R.F. Quiring, 

November 1981. (PB82-158098) 

172 Forecasting Heavy Snow at Wenatchee, Washington. James W. 

Holcomb, December 1981. (PB82-177783) 

173 Central San Joaquin Valley Type Maps. Thomas R. Crossan, 

December 1981. (PB82 196064) 

174 ARAP Test Results. Mark A. Mathewson, December 1981. (PB82 

198103) 

176 Approximations to the Peak Surface Wind Gusts from Desert 

Thunderstorms. Darryl Randerson, June 1982. (PB82 253089) 

177 Climate of Phoenix, Arizona. Robert J. Schmidli and Austin Jamison, 

April 1969 (Revised July 1996). (PB96-191614) 

178 Annual Data and Verification Tabulation, Eastern North Pacific 

Tropical Storms and Hurricanes 1982. E.B. Gunther, June 1983. 

(PB85 106078) 

179 Stratified Maximum Temperature Relationships Between Sixteen Zone 

Stations in Arizona and Respective Key Stations. Ira S. Brenner, June 

1983. (PB83 249904) 

180 Standard Hydrologic Exchange Format (SHEF) Version I. Phillip A. 

Pasteris, Vernon C. Bissel, David G. Bennett, August 1983. (PB85 

106052) 

181 Quantitative and Spacial Distribution of Winter Precipitation along 

Utah's Wasatch Front. Lawrence B. Dunn, August 1983. (PB85 

106912) 

182 500 Millibar Sign Frequency Teleconnection Charts - Winter. 

Lawrence B. Dunn, December 1983. (PB85 106276) 

183 500 Millibar Sign Frequency Teleconnection Charts - Spring. 

Lawrence B. Dunn, January 1984. (PB85 111367) 

184 Collection and Use of Lightning Strike Data in the Western U.S. 

During Summer 1983. Glenn Rasch and Mark Mathewson, February 

1984. (PB85 110534) 

185 500 Millibar Sign Frequency Teleconnection Charts - Summer. 

Lawrence B. Dunn, March 1984. (PB85 111359) 

186 Annual Data and Verification Tabulation eastern North Pacific Tropical 

Storms and Hurricanes 1983. E.B. Gunther, March 1984. (PB85 

109635) 

187 500 Millibar Sign Frequency Teleconnection Charts - Fall. Lawrence 

B. Dunn, May 1984. (PB85-110930) 

188 The Use and Interpretation of Isentropic Analyses. Jeffrey L. 

Anderson, October 1984. (PB85-132694) 
44 

189 Annual Data & Verification Tabulation Eastern North Pacific Tropical 

Storms and Hurricanes 1984. E.B. Gunther and R.L. Cross, April 

1985. (PB85 1878887AS) 

190 Great Salt Lake Effect Snowfall: Some Notes and An Example. David 

M. Carpenter, October 1985. (PB86 119153/AS) 

191 Large Scale Patterns Associated with Major Freeze Episodes in the 

Agricultural Southwest. Ronald S. Hamilton and Glenn R. Lussky, 

December 1985. (PB86 144474AS) 

192 NWR Voice Synthesis Project: Phase I. Glen W. Sampson, January 

1986. (PB86 145604/AS) 

193 The MCC - An Overview and Case Study on Its Impact in the Western 

United States. Glenn R. Lussky, March 1986. (PB86 170651/AS) 

194 Annual Data and Verification Tabulation Eastern North Pacific Tropical 

Storms and Hurricanes 1985. E.B. Gunther and R.L. Cross, March 

1986. (PB86 170941/AS) 

195 Radid Interpretation Guidelines. Roger G. Pappas, March 1986. 

(PB86 177680/AS) 

196 A Mesoscale Convective Complex Type Storm over the Desert 

Southwest. Darryl Randerson, April 1986. (PB86 190998/AS) 

197 The Effects of Eastern North Pacific Tropical Cyclones on the 

Southwestern United States. Walter Smith, August 1986. (PB87 

106258AS) 

198 Preliminary Lightning Climatology Studies for Idaho. Christopher D. 

Hill, Carl J. Gorski, and Michael C. Conger, April 1987. (PB87 

180196/AS) 

199 Heavy Rains and Flooding in Montana: A Case for Slantwise 

Convection. Glenn R. Lussky, April 1987. (PB87 185229/AS) 

200 Annual Data and Verification Tabulation Eastern North Pacific Tropical 

Storms and Hurricanes 1986. Roger L. Cross and Kenneth B. Mielke, 

September 1987. (PB88 110895/AS) 

201 An Inexpensive Solution for the Mass Distribution of Satellite Images. 

Glen W. Sampson and George Clark, September 1987. (PB88 

114038/AS) 

202 Annual Data and Verification Tabulation Eastern North Pacific Tropical 

Storms and Hurricanes 1987. Roger L. Cross and Kenneth B. Mielke, 

September 1988. (PB88-101935/AS) 

203 An Investigation of the 24 September 1986 "Cold Sector" Tornado 

Outbreak in Northern California. John P. Monteverdi and Scott A. 

Braun, October 1988. (PB89 121297/AS) 

204 Preliminary Analysis of Cloud-To-Ground Lightning in the Vicinity of 

the Nevada Test Site. Carven Scott, November 1988. (PB89 

128649/AS) 

205 Forecast Guidelines For Fire Weather and Forecasters -- How 

Nighttime Humidity Affects Wildland Fuels. David W. Goens, 

February 1989. (PB89 162549/AS) 

206 A Collection of Papers Related to Heavy Precipitation Forecasting. 

Western Region Headquarters, Scientific Services Division, August 

1989. (PB89 230833/AS) 

207 The Las Vegas McCarran International Airport Microburst of August 8, 

1989. Carven A. Scott, June 1990. (PB90-240268) 

208 Meteorological Factors Contributing to the Canyon Creek Fire Blowup, 

September 6 and 7, 1988. David W. Goens, June 1990. (PB90-

245085) 

209 Stratus Surge Prediction Along the Central California Coast. Peter 

Felsch and Woodrow Whitlatch, December 1990. (PB91-129239) 

210 Hydrotools. Tom Egger. January 1991. (PB91-151787/AS) 

211 A Northern Utah Soaker. Mark E. Struthwolf, February 1991. (PB91-

168716) 

212 Preliminary Analysis of the San Francisco Rainfall Record: 1849-

1990. Jan Null, May 1991. (PB91-208439) 

213 Idaho Zone Preformat, Temperature Guidance, and Verification. Mark 

A. Mollner, July 1991. (PB91-227405/AS) 

214 Emergency Operational Meteorological Considerations During an 

Accidental Release of Hazardous Chemicals. Peter Mueller and Jerry 

Galt, August 1991. (PB91-235424) 

215 WeatherTools. Tom Egger, October 1991. (PB93-184950) 

216 Creating MOS Equations for RAWS Stations Using Digital Model 

Data. Dennis D. Gettman, December 1991. (PB92-131473/AS) 

217 Forecasting Heavy Snow Events in Missoula, Montana. Mike 

Richmond, May 1992. (PB92-196104) 

218 NWS Winter Weather Workshop in Portland, Oregon. Various 

Authors, December 1992. (PB93-146785) 

219 A Case Study of the Operational Usefulness of the Sharp Workstation 

in Forecasting a Mesocyclone-Induced Cold Sector Tornado Event in 

California. John P. Monteverdi, March 1993. (PB93-178697) 

220 Climate of Pendleton, Oregon. Claudia Bell, August 1993. (PB93-

227536) 

221 Utilization of the Bulk Richardson Number, Helicity and Sounding 

Modification in the Assessment of the Severe Convective Storms of 3 

August 1992. Eric C. Evenson, September 1993. (PB94-131943) 

222 Convective and Rotational Parameters Associated with Three 

Tornado Episodes in Northern and Central California. John P. 

Monteverdi and John Quadros, September 1993. (PB94-131943) 

223 Climate of San Luis Obispo, California. Gary Ryan, February 1994. 

(PB94-162062) 

224 Climate of Wenatchee, Washington. Michael W. McFarland, Roger G. 

Buckman, and Gregory E. Matzen, March 1994. (PB94-164308) 

225 Climate of Santa Barbara, California. Gary Ryan, December 1994. 

(PB95-173720) 

226 Climate of Yakima, Washington. Greg DeVoir, David Hogan, and Jay 

Neher, December 1994. (PB95-173688) 

227 Climate of Kalispell, Montana. Chris Maier, December 1994. (PB95-

169488) 

228 Forecasting Minimum Temperatures in the Santa Maria Agricultural 

District. Wilfred Pi and Peter Felsch, December 1994. (PB95-

171088) 

229 The 10 February 1994 Oroville Tornado--A Case Study. Mike 

Staudenmaier, Jr., April 1995. (PB95-241873) 

230 Santa Ana Winds and the Fire Outbreak of Fall 1993. Ivory Small, 

June 1995. (PB95-241865) 

231 Washington State Tornadoes. Tresté Huse, July 1995. (PB96-

107024) 

232 Fog Climatology at Spokane, Washington. Paul Frisbie, July 1995. 

(PB96-106604) 

233 Storm Relative Isentropic Motion Associated with Cold Fronts in 

Northern Utah. Kevin B. Baker, Kathleen A. Hadley, and Lawrence B. 

Dunn, July 1995. (PB96-106596) 

234 Some Climatological and Synoptic Aspects of Severe Weather 

Development in the Northwestern United States. Eric C. Evenson and 

Robert H. Johns, October 1995. (PB96-112958) 

235 Climate of Las Vegas, Nevada. Paul H. Skrbac and Scott Cordero, 

December 1995. (PB96-135553) 

236 Climate of Astoria, Oregon. Mark A. McInerney, January 1996. 

237 The 6 July 1995 Severe Weather Events in the Northwestern United 

States: Recent Examples of SSWEs. Eric C. Evenson, April 1996. 

238 Significant Weather Patterns Affecting West Central Montana. Joe 

Lester, May 1996. (PB96-178751) 

239 Climate of Portland, Oregon. Clinton C. D. Rockey, May 1996. (PB96-

17603) - First Revision, October 1999 

240 Downslop Winds of Santa Barbara, CA. Gary Ryan, July 1996. 

(PB96-191697) 

241 Operational Applications of the Real-time National Lightning Detection 

Network Data at the NWSO Tucson, AZ. Darren McCollum, David 

Bright, Jim Meyer, and John Glueck, September 1996. (PB97-

108450) 

242 Climate of Pocatello, Idaho. Joe Heim, October 1996. (PB97-

114540) 

243 Climate of Great Falls. Montana. Matt Jackson and D. C. Williamson, 

December 1996. (PB97-126684) 

244 WSR-88D VAD Wind Profile Data Influenced by Bird Migration over 

the Southwest United States. Jesus A. Haro, January 1997. (PB97-

135263) 

245 Climatology of Cape for Eastern Montana and Northern Wyoming. 

Heath Hockenberry and Keith Meier, January 1997. (PB97-133425) 

246 A Western Region Guide to the Eta-29 Model. Mike Staudenmaier, 

Jr., March 1997. (PB97-144075) 

247 The Northeast Nevada Climate Book. Edwin C. Clark, March 1997. 

(First Revision - January 1998 - Andrew S. Gorelow and Edwin C. 

Clark - PB98-123250) 

248 Climate of Eugene, Oregon. Clinton C. D. Rockey, April 1997. 

(PB97-155303) 

249 Climate of Tucson, Arizona. John R. Glueck, October 1997 

250 Northwest Oregon Daily Extremes and Normans. Clinton C. D. 

Rockey, October 1997 

251 A Composite Study Examining Five Heavy Snowfall Patterns for 

South-Central Montana. Jonathan D. Van Ausdall and Thomas W. 

Humphrey. February 1998. (PB98-125255) 

252 Climate of Eureka, California. Alan H. Puffer. February 1998. (PB98-

130735) 

253 Inferenced Oceanic Kelvin/Rossby Wave Influence on North American 

West Coast Precipitation. Martin E. Lee and Dudley Chelton. April 

1998. (PB98-139744) 

254 Conditional Symmetric InstabilityCMethods of Operational Diagnosis 

and Case Study of 23-24 February 1994 Eastern Washington/Oregon 

Snowstorm. Gregory A. DeVoir. May 1998. (PB98-144660) 

255 Creation and Maintenance of a Comprehensive Climate Data Base. 

Eugene Petrescu. August 1998. (PB98-173529) 

256 Climate of San Diego, California. Thomas E. Evans, III and Donald A. 

Halvorson. October 1998. (PB99-109381) 

257 Climate of Seattle, Washington. Dana Felton. November 1998. 

(PB99-113482) 

258 1985-1998 North Pacific Tropical Cyclones Impacting the 

Southwestern United States and Northern Mexico: An Updated 

Climatology. Armando L. Garza. January 1999. (PB99-130502) 

259 Climate of San Jose, California. Miguel Miller. April 1999. (PB99-

145633) 

260 Climate of Las Vegas, Nevada. Paul H. Skrbac. December 1999 

261 Climate of Los Angeles, California. David Bruno, Gary Ryan, with 

assistance from Curt Kaplan and Jonathan Slemmer. January 2000 

262 Climate of Miles City, Montana. David A. Spector and Mark H. 

Strobin. April 2000 

263 Analysis of Radiosonde Data for Spokane, Washington. Rocco D. 

Pelatti. November 2000 

264 Climate of Billings, Montana. Jeffrey J. Zeltwanger and Mark H. 

Strobin. November 2000 

265 Climate of Sheridan, Wyoming. Jeffrey J. Zeltwanger, Sally Springer, 

Mark H. Strobin. March 2001 

266 Climate of Sacramento, California. Laura Masters-Bevan. December 

2000 (7th Revision) 

267 Sulphur Mountain Doppler Radar: A Performance Study. Los 

Angeles/Oxnard WFO. August 2001 

268 Prediction of Heavy Snow Events in the Snake River Plain Using 

Pattern Recognition and Regression Techniques. Thomas Andretta 

and William Wojcik. October 2003 

269 The Lewis and Clark Expedition 18-03-1806, Weather, Water and 

Climate, Vernon Preston, Pocatello Idaho, December 2004. 
45 

270 Climate of San Diego, California, Emmanuel M. Isla, September 2004 

(2nd Edition) 

271 Climate of Las Vegas, Nevada, Andrew S. Gorelow, January 2005, 

(2nd Edition) 

272 Climate of Sacramento, California, Revised by: Laura A. Bevan and 

George Cline, June 2005 

273 Climate of Flagstaff, AZ 4th Revision. Mike Staudenmaier, Jr, Reginald 

Preston(R) Paul Sorenson (R) , August 2005 

274 Climate of Prescott, AZ, Bob Fogarty, Mike Staudenmaier Jr., 

Flagstaff WFO, AZ, August 2005. 

275 Climate of San Diego, CA, 3rd Revision. Noel M. Isla, Jennifer Lee, 

March 2006 

276 Climate of Reno, NV, Brian Ohara, Reno, NV October 2006 

277 Forecaster's Handbook for Extreme Southwestern California Based 

On Short Term Climatalogical Approximations: Part I - The Marine 

Layer and Its Effect On Precipitation and Heating Ivory J. Small, 

October 2006 

278 Forecaster's Handbook for Extreme Southwestern California Based 

On Short Term Climatalogical Approximations: Part II – Wind Effects 

on Terrestrial and Marine Environments Ivory J. Small, December 

2006 

279 Effects of Wildfire in the Mountainous Terrain of Southeast Arizona: 

An Empirical Formula to Estimate 5-Year Peak Discharge from Small 

Post-Burn Watersheds, William B. Reed and Mike Schaffner , June 

2007 

280 Climate of Fresno, California, Chris Stachelski, Gary Sanger, February 

2008 

281 Climate of Bakersfield, California, Chris Stachelski, Gary Sanger 

February 2008 

282 Hazardous Weather Climatology for Arizona - Craig Shoemaker, 

Jeffrey T. Davis. February, 2008 
46 

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TECHNICAL PUBLICATIONS 

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47 

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