Mesoscale Discussion

MESOSCALE DISCUSSION 0820
NWS STORM PREDICTION CENTER NORMAN OK
1007 AM CDT THU MAY 08 2008

AREAS AFFECTED...NRN MS...CNTRL/NRN AL INTO MIDDLE/ERN TN

CONCERNING...TORNADO WATCH 277...

VALID 081507Z - 081630Z

THE SEVERE WEATHER THREAT FOR TORNADO WATCH 277 CONTINUES.

AN ADDITIONAL WW MAY BE NEEDED BY EARLY AFTERNOON TO INCLUDE MUCH OF
CENTRAL AND THE REMAINDER OF NORTHERN ALABAMA.

AS WEAKENING MID-LEVEL CIRCULATION CONTINUES TO LIFT EAST NORTHEAST
OF THE OZARK PLATEAU INTO THE LOWER OHIO VALLEY...THE TENDENCY WILL
BE FOR ASSOCIATED STRONGER MID-LEVEL FORCING TO SPREAD ACROSS THE
TENNESSEE VALLEY TOWARD THE SOUTHERN APPALACHIANS. LOW-LEVEL
ENVIRONMENT ACROSS NORTHWEST GEORGIA/NORTHEAST ALABAMA INTO EASTERN
TENNESSEE REMAINS DRY...AND INCREASING PRECIPITATION NEXT FEW HOURS
MAY MAINTAIN A STABLE BOUNDARY LAYER ACROSS THIS REGION.

AT THE SAME TIME...A WARMING...SUBSIDENT MID-LEVEL REGIME MAY BECOME
INCREASINGLY SUPPRESSIVE OF CONVECTIVE DEVELOPMENT TO THE WEST/SOUTH
OF ONGOING NARROW FRONTAL SQUALL LINE...WHICH MODELS SUGGEST WILL
ADVANCE INTO AREAS WEST OF FLORENCE AL/COLUMBUS MS BY 17-18Z. RISK
FOR LARGE HAIL/DAMAGING WIND GUSTS MAY BECOME THE MOST PROMINENT
SEVERE THREAT WITH THIS LINE.

LONGER TERM SEVERE THREAT WITH ISOLATED SUPER CELLULAR ACTIVITY IN
WARM ADVECTION REGIME DOWNSTREAM OF SQUALL LINE IS MORE UNCERTAIN AS
IT LIFTS EAST NORTHEAST OF FLORENCE/MUSCLE SHOALS...INTO A MORE
STABLE BOUNDARY LAYER ACROSS SOUTHERN MIDDLE TENNESSEE THE NEXT FEW
HOURS. BUT...LATEST RUC GUIDANCE IS SUGGESTIVE THAT INHIBITION MAY
BECOME WEAK ENOUGH WITH DAYTIME HEATING TO SUPPORT ADDITIONAL
ISOLATED CONVECTIVE DEVELOPMENT ACROSS CENTRAL/NORTHERN ALABAMA BY
18-19Z. IF THIS OCCURS...DEEP LAYER SHEAR IN AN ENVIRONMENT WITH
MIXED LAYER CAPE IN EXCESS OF 1000 J/KG WILL BE FAVORABLE FOR
SUPERCELLS. AND...LOW-LEVEL HODOGRAPHS BENEATH A 40-50 KT
SOUTHWESTERLY LOW-LEVEL JET AXIS WILL BE LARGE AND SUPPORTIVE OF THE
POTENTIAL FOR TORNADOES.