Transcript The May 24 Shamrock cold front University of Wyoming

The May 24 Shamrock cold front
A King Air/ WCR close-up view
Bart Geerts & Dave Leon
University of Wyoming
Synoptic situation at 18 UTC on 24 May 2002, based on the ETA initialization. Equivalent
potential temperature (color field) and winds (blue, a full barb equals 10 kts) at 900 mb, sea
level pressure (yellow contours), and 300 mb geopotential height (red contours).
18 Z
21 Z
8 dropsondes,
20:22 - 20:57 Z
GOES 8 visible satellite image, operational surface observations, and subjective frontal analysis
mixing
ratio
pressure (mb)
q
cold front
west
total distance: 217 km
east
TX OK
cold
front
dryline
radial velocity
reflectivity
19:00 Z
Smart-R and mobile mesonet data
Td=9°C
r = 7.4 g/kg
19:30 Z
Td=15°C
r =11.4 g/kg
20:00 Z
20:30 Z
5/24, 21:07 UTC
19:42 UTC
AMA
19:52
UWKA
N
19:43
cold front
dryline
WCR up-looking, flight level 165 m
WCR vertical velocities
dryline
cold front
Triple point transect
20:12
Flight level: ~2300 m AGL
King Air
cold front
@20:09
20:07
frontal motion
SSE
164
NNW
344
moist air
front
& dryline
cold air
Flight level: 2300 m AGL
WCR nadir antenna reflectivity
frontal motion
dBZ
reflectivity
1:1 aspect ratio
Height
above
flight
level
(m)
NW flight level: 360 m AGL
315
frontal
motion
total length: 11.2 km
aspect ratio: 1:1
SE
135
19:33 - 19:35:33
possibly stratus clouds
frontal motion
WNW
344
km
ESE
164
20:21:50 - 20:25:40
-5
NNW
344
SSE
164
1.5
8 6
dBZ
km
2.0
1.0
0.5
-45
20:27:00 - 20:30:48
km
NW
300
SE
120
20:42:43 - 20:46:18
21:06:36-21:13:20
Gravity waves in the
cold-frontal stratus
frontal motion
This is a cloud whose
towering tops had
grown well above 4
km AGL, part of a line
of storm cells aligned
with the cold front
mixing
ratio
9 km
Deep convection develops 9
km ahead of sfc cold front
w
21:05
21:15
wind
direction
21:32
q
WNW
290
qe
ESE
110
summary
• An airborne W-band radar sampling at 30 Hz & a resolution of ~25 m can
measure echoes in the opticaly-clear warm-season CBL.
• Dual-Doppler synthesis at close range is feasible.
• The WCR echo and velocity transects confirming kinematic aspects of a
cold front that have been simulated in the lab and by hi-res numerical
models, but have never been observed before.