MESO: Mesoscale Discussion 2198

ACUS11 KWNS 251903
SWOMCD
SPC MCD 251903
TNZ000-MSZ000-ARZ000-252130-

MESOSCALE DISCUSSION 2198
NWS STORM PREDICTION CENTER NORMAN OK
0203 PM CDT SUN SEP 25 2011

AREAS AFFECTED...SCNTRL THROUGH ERN AR INTO NWRN MS AND WRN TN

CONCERNING...SEVERE POTENTIAL...WATCH LIKELY

VALID 251903Z - 252130Z

THUNDERSTORMS ARE EXPECTED TO DEVELOP ACROSS SCNTRL THROUGH ERN AR
AND WRN TN BY 20-22Z. THREAT WILL EXIST FOR SUPERCELLS AND BOWING
SEGMENTS WITH LARGE HAIL...ISOLATED TORNADOES AND DAMAGING WIND
THROUGH MID EVENING. A WW MAY BE NEEDED BY 20Z-21Z.

QUASI-STATIONARY FRONT EXTENDS FROM CNTRL KY SWWD THROUGH WRN
TN...CNTRL AR AND N-CNTRL TX. THIS FRONT SHOULD SHIFT SWD THROUGH
THE LOWER MS VALLEY THIS EVENING AS PRIMARY SURFACE LOW DEVELOPS
THROUGH THE WRN TN VALLEY AND SWRN PORTIONS OF THE OH VALLEY. THE
WARM SECTOR HAS BECOME MODERATELY TO STRONGLY UNSTABLE ESPECIALLY
ACROSS SRN AR WHERE PLUME OF 7.5-8 C/KM MID LEVEL LAPSE RATES HAVE
OVERSPREAD MOIST AXIS RESULTING IN 2500 J/KG MLCAPE. THE BOUNDARY
LAYER REMAINS CAPPED. HOWEVER...CIRRUS IS DEVELOPING OVER THE LOWER
MS VALLEY AND APPEARS TO BE A RESULT OF ASCENT WITHIN EXIT REGION OF
AN UPPER JET MOVING SWD ALONG WRN PERIPHERY OF CUTOFF UPPER LOW.
COMBINATION OF DIABATIC WARMING AND DEEPER ASCENT WITHIN FRONTAL
ZONE SHOULD EVENTUALLY PROMOTE THUNDERSTORM DEVELOPMENT WITHIN THE
NEXT COUPLE OF HOURS. BOUNDARY LAYER WINDS HAVE VEERED TO SSWLY OVER
SRN AR WHERE THE ATMOSPHERE IS MOST UNSTABLE. LARGEST HODOGRAPHS
EXIST FARTHER EAST ALONG MIGRATORY LLJ AXIS OVER WRN PORTIONS OF THE
TN VALLEY. EFFECTIVE BULK SHEAR FROM 35-45 KT AND EXPECTED STORM
RELATIVE HELICITY FROM 150-300 M2/S2 WILL SUPPORT ORGANIZED STORMS
INCLUDING SUPERCELLS. STORMS SHOULD EVENTUALLY TRANSITION TO MIXED
MODES WITH POTENTIAL FOR BOWING LINE SEGMENTS.

..DIAL.. 09/25/2011

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

ATTN...WFO...MEG...JAN...LZK...SHV...

LAT...LON 33259306 34749335 35998943 35478874 34738957 33329134
33259306

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