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 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.) Related to the vertical structure of atmosphere

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

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

7. Dust Devil in Arizona www.nasa.gov

8. Mountain Strongest wind speed Mountain waves Roll cloud Lee waves Dust may be visible ACSL clouds Cap cloud Cloudy, cooler, possible fog & precip 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. KPRC 081953Z 19008G15KT 160V220 10SM CLR 29/01 A2999 RMK AO2 PK WND 13027/1921 SLP060 VIRGA N-E TCU W-SE T02890006 KPRC 082053Z 25011G17KT 10SM CLR 32/M01 A2998 RMK AO2 SLP052 T03221011 56010 KPRC 082153Z 25013G18KT 10SM CLR 32/M01 A2996 RMK AO2 SLP048 ACFT MISHAP T03171006 ERAU Aircraft #N519ER 08 June 2003 Virga

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

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: http://meteo.pr.erau.edu/links.php)http://meteo.pr.erau.edu/links.php

18. (http://rucsoundings.noaa.gov/gifs/)

19. ALTPRESDIRSPDTEMPDEWP LAYERMECHTHERMCLOUD ftmbC°ktCC ft (MSL)TURB? LAYERLCL (ft) 4895 84514422244.3 4895 - 4950TURB 4950 84314324234.3 4950 - 5068TURB 5068 8401442522.64.2 5068 - 5246TURB 5246 83514526224.1 5246 - 5479TURB 5479 8281452721.34 5479 - 5836 5836 8171472720.23.7 5836 - 6197TURB 6197 8071482719.13.5 6197 - 6558TURB 6558 79715027183.3 6558 - 6925 6925 78615126173.1 6925 - 7296TURB 7296 7761532615.92.8 7296 - 7667TURB 7667 7661562514.82.5 7667 - 8044 8044 7551582413.72.2 8044 - 8425TURB 8425 7451622312.61.8 8425 - 8809 8809 7351672211.61.3 8809 - 9199 9199 7241732110.60.6 9199 - 9593TURB 9593 714189189.6-0.4 9593 - 9990TURB 9990 704213188.8-2.6 9990 - 10141TURB 12,775 24330 40025942-25.6-28.2 24330 - 24888 CLOUD 24888 39025443-27-29.2 24888 - 30561 CLOUD

20. Dry thermals Convectively unstable layer

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 (http://rucsoundings.noaa.gov/gifs/)http://rucsoundings.noaa.gov/gifs/ Spreadsheet tool is available on the ERAU Department of Meteorology website (http://meteo.pr.erau.edu/links.php)http://meteo.pr.erau.edu/links.php Questions?