Mesoscale Discussion 2139

Issued

Dec 9, 2012, 12:38 PM CST (18:38 UTC)

Expired

Dec 9, 2012, 2:45 PM CST

In force

2 hr

Issued by

the Storm Prediction Center

Chance of a watch

40%

The Little Rock radar (KLZK), 76 km from the middle of the area, began a volume at 18:40 UTC, the scan nearest the moment this went out.

Open the radar archive at this moment

The archived warnings, watches and discussions in force at that minute are drawn over the scan, this one among them.

• Tornado Watch 677Dec 9, 2:10 PM CST

423 
ACUS11 KWNS 091839
SWOMCD
SPC MCD 091838
KYZ000-TNZ000-ILZ000-MOZ000-ARZ000-MSZ000-092045-

MESOSCALE DISCUSSION 2139
NWS STORM PREDICTION CENTER NORMAN OK
1238 PM CST SUN DEC 09 2012

AREAS AFFECTED...SWRN INTO NERN AR...SERN MO...FAR SRN IL...WRN
KY/TN

CONCERNING...SEVERE POTENTIAL...WATCH POSSIBLE

VALID 091838Z - 092045Z

PROBABILITY OF WATCH ISSUANCE...40 PERCENT

SUMMARY...PORTIONS OF SWRN INTO NERN AR...SERN MO...FAR SRN IL...AND
WRN KY/TN ARE BEING MONITORED FOR A WW THIS AFTERNOON. PRIMARY SVR
WEATHER THREAT WILL BE LARGE HAIL/DAMAGING WIND GUSTS...THOUGH A
TORNADO OR TWO WILL ALSO BE POSSIBLE.

DISCUSSION...EARLY AFTERNOON SURFACE ANALYSIS PLACES AN AREA OF LOW
PRESSURE OVER CNTRL AR...WITH A COLD FRONT EXTENDING SWWD INTO CNTRL
TX...AND A WARM FRONT SLOWLY RETREATING NWD OVER WRN/CNTRL KY. AS AN
UPPER TROUGH CONSOLIDATES AND DEEPENS OVER THE CNTRL CONUS THIS
AFTERNOON/EVENING...THE SURFACE LOW IS FORECAST TO EJECT NEWD INTO
THE LOWER OH VALLEY...AND THE WARM FRONT WILL CONTINUE LIFTING NWD
INTO SRN IND/OH.

MEANWHILE...A 30-40 KT SWLY LLJ HAS AIDED IN TRANSPORTING LOW TO MID
60F DEWPOINTS ALONG AN AXIS FROM SWRN AR INTO WRN KY/TN. IN
ADDITION...POCKETS OF CLEARING OVER AR HAVE ALLOWED TEMPERATURES TO
LOCALLY WARM TO AROUND 70F...WHICH HAS AIDED IN BOUNDARY LAYER
DESTABILIZATION AND THE DEVELOPMENT OF AGITATED CUMULUS CLOUD
STREETS. WV AND VIS SATELLITE IMAGERY SHOW A PLUME OF HIGH LEVEL
CLOUDINESS OVERSPREADING THE REGION...WHICH MAY INFER THE APPROACH
OF A SUBTLE UPPER-LEVEL DISTURBANCE. ASCENT ASSOCIATED WITH THAT
FEATURE COMBINED WITH CONTINUED SURFACE HEATING...CONTRIBUTING
TOWARD SBCAPE VALUES FROM 500-1500 J/KG...MAY AID IN GRADUAL
DEEPENING OF THE CUMULUS FIELD OVER AR AND EVENTUAL SCATTERED
THUNDERSTORM DEVELOPMENT BY MID AFTERNOON.

OTHERWISE...ASCENT ALONG THE COLD FRONT WILL STRENGTHEN BY LATE
AFTERNOON/EVENING...AND BE SUFFICIENT FOR THE DEVELOPMENT OF
SCATTERED TO NUMEROUS STORMS FROM WRN KY INTO SRN AR. IF CELLULAR
ACTIVITY CAN DEVELOP DURING THE AFTERNOON...THEN DEEP-LAYER SHEAR
NEAR 50 KT WILL FAVOR SUPERCELLS. IF STORMS QUICKLY ORGANIZE INTO
LINES ALONG THE FRONT LATE THIS AFTERNOON/EVENING...THEN BOWING/LEWP
STRUCTURES WILL BE MORE LIKELY. LARGE HAIL AND DAMAGING WIND GUSTS
WILL BE THE PRIMARY SVR WEATHER THREATS WITH EITHER MODE OF
CONVECTION. HOWEVER...A TORNADO OR TWO WILL BE POSSIBLE AS THE 30-40
KT SWLY LLJ AIDS IN EFFECTIVE SRH VALUES FROM 150-250 M2 S-2.

..GARNER/HART.. 12/09/2012

...PLEASE SEE WWW.SPC.NOAA.GOV FOR GRAPHIC PRODUCT...

ATTN...WFO...PAH...MEG...LZK...SGF...SHV...

LAT...LON   34079436 35209349 36749090 37378894 37028801 35708856
            33819192 33339390 34079436

Mesoscale Discussions in Arkansas, 2012Mesoscale Discussions in Tennessee, 2012Mesoscale Discussions in Kentucky, 2012Every mesoscale discussion in 2012

The product and its follow-ups from the Iowa Environmental Mesonet's archive of National Weather Service and Storm Prediction Center text; the sounding from the Mesonet's radiosonde archive; radar from the NEXRAD Level II archive.