Transcript Slide 1
Anticipating Aviation Weather Hazards in the Southwest Dr. Curtis N. James Department of Meteorology Prescott, Arizona 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? 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 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 Deep convective boundary layer (more stable air above) 20,000’ MSL or more thermal thermal dust devil Hot, dry, unstable air Convective boundary layer (Prescott, AZ) Fall 2000—Photo by Joe Aldrich Dust Devil in Arizona www.nasa.gov www.nasa.gov Mountain waves ACSL clouds Strongest wind speed Roll cloud Cap cloud Cloudy, cooler, possible fog & precip Lee waves Mountain Clear, warm, dry & windy Dust may be visible Mountain wave clouds (PRC) 2000—Photo by Ben Small Lenticular clouds (near Denver) 2000—Photo by Josh Richmeier 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 Downburst (Phoenix, AZ) July 2003—Photo by Phillip Zygmunt Downburst (Prescott Valley, AZ) 1999—Photo by Jacob Neider ERAU Aircraft #N519ER 08 June 2003 Virga 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 Kingman, AZ ERAU Aircraft #N518ER 29 November 2003 Stable air over less stable air, increasing wind speed with height Downslope wind? 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) 1000 T p 0.286 ( potentialtem perature) Lv w (equivalent potentialtem p.) e exp c T p g T z Rb ( Bulk Richardson) 2 2 U V z z (http://rucsoundings.noaa.gov/gifs/) ALT PRES DIR SPD TEMP DEWP LAYER MECH THERM CLOUD CLOUD ft mb C° kt C C ft (MSL) TURB? TURB? LAYER LCL (ft) 4895 845 144 22 24 4.3 4895 - 4950 TURB TURB 4950 843 143 24 23 4.3 4950 - 5068 TURB TURB 5068 840 144 25 22.6 4.2 5068 - 5246 TURB TURB 5246 835 145 26 22 4.1 5246 - 5479 TURB 5479 828 145 27 21.3 4 5479 - 5836 5836 817 147 27 20.2 3.7 5836 - 6197 TURB TURB 6197 807 148 27 19.1 3.5 6197 - 6558 TURB TURB 6558 797 150 27 18 3.3 6558 - 6925 6925 786 151 26 17 3.1 6925 - 7296 TURB TURB 7296 776 153 26 15.9 2.8 7296 - 7667 TURB TURB 7667 766 156 25 14.8 2.5 7667 - 8044 8044 755 158 24 13.7 2.2 8044 - 8425 TURB TURB 8425 745 162 23 12.6 1.8 8425 - 8809 8809 735 167 22 11.6 1.3 8809 - 9199 9199 724 173 21 10.6 0.6 9199 - 9593 TURB 9593 714 189 18 9.6 -0.4 9593 - 9990 TURB 9990 704 213 18 8.8 -2.6 9990 - 10141 TURB 24330 400 259 42 -25.6 -28.2 24330 - 24888 CLOUD 24888 390 254 43 -27 -29.2 24888 - 30561 CLOUD 12,775 Potential Tem perature and Equivalent Potential Tem perature Profiles 60000 50000 Height (Feet) 40000 θ (Kelvins) Dry parcel 30000 Convectively unstable layer θe,s (Kelvins) Wet parcel 20000 10000 0 260 Dry thermals 280 300 320 Tem perature (Kelvins) 340 360 380 WSR-88D Radar Images NM/Holloman AFB 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/) • Spreadsheet tool is available on the ERAU Department of Meteorology website (http://meteo.pr.erau.edu/links.php) Questions?