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?