1. The May 24 Shamrock cold front
A King Air/ WCR close-up view
Bart Geerts & Dave Leon
University of Wyoming

2. 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).

3. 18 Z
21 Z
8 dropsondes,
20: :57 Z
GOES 8 visible satellite image, operational surface observations, and subjective frontal analysis

4. q cold front east west total distance: 217 km mixing ratio
pressure (mb)
cold front
east
west
total distance: 217 km

5. Smart-R and mobile mesonet data
TX OK
cold front
dryline
reflectivity
radial velocity
19:00 Z
Td=9°C r = 7.4 g/kg
Smart-R and mobile mesonet data

6. 19:30 Z
Td=15°C r =11.4 g/kg

7. 20:00 Z

8. 20:30 Z

9. 5/24, 21:07 UTC

10. N 19:42 UTC WCR up-looking, flight level 165 m 19:52 UWKA 19:43
AMA
19:52
UWKA N
19:43
cold front
dryline
WCR up-looking, flight level 165 m

12. WCR vertical velocities
dryline
cold front

13. Triple point transect Flight level: ~2300 m AGL King Air 20:12 20:07
cold
20:07
frontal motion
SSE
164
NNW
344
front
& dryline
moist air
cold air

14. dBZ Flight level: 2300 m AGL WCR nadir antenna reflectivity
frontal motion
dBZ

15. reflectivity
1:1 aspect ratio

17. 8 6 frontal motion km NW 315 SE 135 WNW 344 ESE 164 -5 km NNW 344 SSE
Height above
flight level
(m)
total length: 11.2 km
aspect ratio: 1:1 NW
315
flight level: 360 m AGL
frontal motion SE
135
19: :35:33
possibly stratus clouds
frontal motion
WNW
344
ESE
164 km
20:21: :25:40 -5 km
NNW
344
SSE
164
2.0
1.5
1.0
0.5 8 6
dBZ
-45
20:27: :30:48 km NW
300 SE
120
20:42: :46:18

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 qe
WNW
290
ESE
110

19. 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.