1. Anticipating Aviation Weather Hazards in the Southwest
Dr. Curtis N. James
Department of Meteorology
Prescott, Arizona

2. Overview
What are some general characteristics of the climate of the Southwest?
How is aviation affected by this climate?
How can the aviation weather hazards be anticipated and avoided?
Why is an understanding of the vertical structure of the atmosphere necessary?

3. General Climate of the Southwest
Located in a latitude belt (~30°) where air generally sinks and warms (usually clear & dry; 300+ flying days / year)
Rugged terrain (clouds/precip usually more frequent over windward slopes w/ lee rain shadowing & waves)
Continental climate, isolated from oceans by terrain (generally dry air w/ high temperature variability)
Prevailing surface wind generally southwesterly (except where terrain generates local winds)
Prevailing wind aloft westerly in cold season, southerly in summer (associated with the SW monsoon)
In warm season, deep convective layer near the ground

4. Aviation Hazards of the Southwest
Related to the vertical structure of atmosphere
Deep convective boundary layer
Low-level turbulence and dust devils
Thunderstorms (esp. July – September)
Downbursts (especially dry microbursts)
Hail, lightning, turbulence near thunderstorms
Mountain waves / shears & lee turbulence
Other (icing, low clouds, IMC, LLWS, etc.)

5. Deep convective boundary layer
(more stable air above)
20,000’ MSL or more
thermal
dust devil
Hot, dry, unstable air

6. Convective boundary layer (Prescott, AZ)
Fall 2000—Photo by Joe Aldrich

7. Dust Devil in Arizona

8. Mountain waves ACSL clouds Strongest wind speed Roll cloud Cap cloud
Cloudy, cooler, possible fog & precip
Lee waves
Mountain
Dust may be visible
Clear, warm, dry & windy

9. Mountain wave clouds (PRC)
2000—Photo by Ben Small

10. Lenticular clouds (near Denver)
2000—Photo by Josh Richmeier

11. Dry microbursts
When precipitation falls through unsaturated air, evaporative cooling may produce dry microbursts
Result in very hazardous shear conditions
Visual clue: fallstreaks or virga (fall streaks that don’t reach the ground)
Flight path of plane
45 kt downburst
45 kt headwind
45 kt tailwind

12. Downburst (Phoenix, AZ)
July 2003—Photo by Phillip Zygmunt

13. Downburst (Prescott Valley, AZ)
1999—Photo by Jacob Neider

15. ERAU Aircraft #N519ER 08 June 2003
Virga
KPRC Z 19008G15KT 160V220 10SM CLR 29/01 A2999 RMK AO2 PK WND 13027/1921 SLP060 VIRGA N-E TCU W-SE T
KPRC Z 25011G17KT 10SM CLR 32/M01 A2998 RMK AO2 SLP052 T
KPRC Z 25013G18KT 10SM CLR 32/M01 A2996 RMK AO2 SLP048 ACFT MISHAP T

16. ERAU Aircraft #N518ER 29 November 2003
Kingman, AZ
Stable air over less stable air, increasing
wind speed with height
Downslope
wind?

17. Vertical structure of atmosphere
The following three parameters can be used to anticipate most of the hazards in a forecast vertical sounding:
(Analysis Tool:

18. (

19. ALT
PRES
DIR
SPD
TEMP
DEWP
LAYER
MECH
THERM
CLOUD ft mb C° kt C
ft (MSL)
TURB?
LCL (ft)
4895
845
144 22 24
4.3
TURB
4950
843
143 23
5068
840 25
22.6
4.2
5246
835
145 26
4.1
5479
828 27
21.3 4
5836
817
147
20.2
3.7
6197
807
148
19.1
3.5
6558
797
150 18
3.3
6925
786
151 17
3.1
7296
776
153
15.9
2.8
7667
766
156
14.8
2.5
8044
755
158
13.7
2.2
8425
745
162
12.6
1.8
8809
735
167
11.6
1.3
9199
724
173 21
10.6
0.6
9593
714
189
9.6
-0.4
9990
704
213
8.8
-2.6
12,775 
24330
400
259 42
-25.6
-28.2
24888
390
254 43
-27
-29.2

20. Convectively
unstable layer
Dry thermals

21. WSR-88D Radar Images
NM/Holloman AFB

22. Summary
The Southwest has a fascinating climate, with a number of aviation hazards
Many hazards may be anticipated using a vertical profile of the atmosphere
Suggest analyze forecast sounding prior to flight (
Spreadsheet tool is available on the ERAU Department of Meteorology website (
Questions?