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).

 

GOES 8 visible satellite image, operational surface observations, and subjective frontal analysis

18 Z 21 Z

8 dropsondes,20:22 - 20:57 Z

mixing ratio

total distance: 217 kmwest east

cold front

pres

sure

(m

b)

19:00 Z

reflectivity radial velocity

cold front

dryline

Smart-R and mobile mesonet data

TX OK

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

19:43

19:52

UWKA

19:42 UTC

AMA

cold front

dryline

WCR up-looking, flight level 165 m

N

WCR vertical velocities

dryline cold front

Flight level: ~2300 m AGL

Triple point transect

SSE164

NNW344

front & drylinemoist air cold air

frontal motion

20:07

20:12

cold front @20:09

King Air

WCR nadir antenna reflectivityFlight level: 2300 m AGL

dBZ

frontal motion

reflectivity

1:1 aspect ratio

20:21:50 - 20:25:40

frontal motion

km

possibly stratus clouds

km-5

SE120

NW300

km

20:42:43 - 20:46:18

ESE164

SE135

NW315

Height aboveflight level(m)

frontal motion

flight level: 360 m AGL total length: 11.2 kmaspect ratio: 1:1

WNW344

19:33 - 19:35:33

-45

dBZ

SSE164

NNW344

68

20:27:00 - 20:30:48

2.0

1.5

1.0

0.5

21:06:36-21:13:20

ESE110

WNW290

frontal motionThis 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

Deep convection develops 9 km ahead of sfc cold front

9 km

Gravity waves in the cold-frontal stratus

21:32

21:05 21:15

w

mixing ratio

e

wind direction

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.