Anticipating Aviation Weather Anticipating Aviation Weather Hazards in the SouthwestHazards in the Southwest

Dr. Curtis N. JamesDr. Curtis N. JamesDepartment of MeteorologyDepartment of Meteorology

Prescott, ArizonaPrescott, Arizona

OverviewOverview

• 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 SouthwestGeneral 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 SouthwestAviation 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 layerDeep convective boundary layer

20,000’ MSL or more

(more stable air above)

Hot, dry, unstable air

dust devil

thermal thermal

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

Dust Devil in Arizonawww.nasa.govwww.nasa.gov

Mountain

Strongest wind speed

Mountain wavesMountain waves

Roll cloud

Lee waves

Dust may be visible

ACSL clouds

Cap cloudCloudy,

cooler, possible fog & precip

Clear, warm, dry & windy

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

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

Dry microburstsDry 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

KPRC 081953Z 19008G15KT 160V220 10SM CLR 29/01 A2999 RMK AO2 PK WND 13027/1921 SLP060 VIRGA N-E TCU W-SE T02890006KPRC 082053Z 25011G17KT 10SM CLR 32/M01 A2998 RMK AO2 SLP052 T03221011 56010KPRC 082153Z 25013G18KT 10SM CLR 32/M01 A2996 RMK AO2 SLP048 ACFT MISHAP T03171006

ERAU Aircraft #N519ER

08 June 2003

Virga

ERAU Aircraft #N518ER29 November 2003

Downslopewind?

Stable air over less stable air, increasingwind speed with height

Kingman, AZ

Vertical structure of atmosphereVertical structure of atmosphere

)(

.)(exp

)(1000

22

286.0

RichardsonBulk

zV

zU

zTg

R

temppotentialequivalentTc

wL

etemperaturpotentialp

T

b

p

ve

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://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     12,775 

24330 400 259 42 -25.6 -28.2   24330 - 24888     CLOUD  

24888 390 254 43 -27 -29.2   24888 - 30561     CLOUD  

Potential Temperature and Equivalent Potential Temperature Profiles

0

10000

20000

30000

40000

50000

60000

260 280 300 320 340 360 380

Temperature (Kelvins)

Hei

gh

t (F

eet) θ (Kelvins)

Dry parcel

θe,s (Kelvins)

Wet parcel

Dry thermals

Convectivelyunstable layer

WSR-88D Radar Images NM/Holloman AFB

SummarySummary

• 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?