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MESOSCALE DISCUSSION 0120
NWS STORM PREDICTION CENTER NORMAN OK
1114 AM CST WED FEB 18 2009

AREAS AFFECTED…PORTIONS OF NERN AND CNTRL MS INTO NWRN AND W-CNTRL
AL

CONCERNING…SEVERE POTENTIAL…WATCH POSSIBLE

VALID 181714Z – 181845Z

THE POTENTIAL FOR SEVERE STORMS CAPABLE OF LARGE HAIL…DAMAGING
WINDS AND PERHAPS A FEW TORNADOES IS EXPECTED TO INCREASE THIS
AFTERNOON. CONVECTIVE TRENDS ARE BEING MONITORED FOR A POSSIBLE WW.

LATEST TRENDS IN VISIBLE SATELLITE IMAGERY INDICATE DEEPENING
CUMULUS BANDS ORIENTED WSW-ENE WITHIN PRE-FRONTAL WARM SECTOR FROM W
OF THE I-65 CORRIDOR IN MIDDLE TN SWWD INTO CNTRL MS. WHILE
BOUNDARY LAYER IS NOT OVERLY MOIST /DEWPOINTS IN THE UPPER 50S TO
LOWER 60S/…STRONG DAYTIME HEATING IS CONTRIBUTING TO THE
DEVELOPMENT OF STEEP LOW-LEVEL LAPSE RATES AND RESULTANT MLCAPE OF
AROUND 500 J/KG. OF CONCERN TO STORM INITIATION ARE: 1/ WEAK
CONVERGENCE ALONG COLD FRONT…AND 2/ INFERRED MIDLEVEL SUBSIDENCE
AND RESULTING POOR MIDLEVEL LAPSE RATES PER WATER VAPOR IMAGERY AND
RUC OBJECTIVE FIELDS. THUS…CONSIDERABLE UNCERTAINTY EXISTS WITH
REGARD TO THE TIMING AND LOCATION OF ANY ADDITIONAL STORM
DEVELOPMENT TO THE S OF ONGOING STORMS OVER S-CNTRL KY INTO MIDDLE
TN.

ONCE STORMS DEVELOP AND BECOME SUSTAINED…THE PRESENCE OF 60-70 KT
DEEP LAYER SHEAR AND LONG…STRAIGHT HODOGRAPHS WILL SUPPORT
SUPERCELL DEVELOPMENT /SOME SPLITTING/ WITH THE THREAT FOR DAMAGING
WINDS…LARGE HAIL AND PERHAPS A FEW TORNADOES.

..MEAD.. 02/18/2009

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