Mesoscale Discussion 773

MESOSCALE DISCUSSION 0773
NWS STORM PREDICTION CENTER NORMAN OK
1212 PM CDT FRI MAY 02 2008
AREAS AFFECTED...WRN TN/KY...NRN/WRN MS...LA
CONCERNING...TORNADO WATCH
249
...
250
...
VALID 021712Z - 021915Z
THE SEVERE WEATHER THREAT FOR TORNADO WATCH 249...250...CONTINUES.
ADDITIONAL WWS MAY BE NEEDED EAST/SOUTHEAST OF WW 249. BUT...THE
PRIMARY TORNADO THREAT WITH POTENTIALLY LONG-LIVED SUPERCELLS MAY
SHIFT INTO PARTS OF WESTERN KENTUCKY/TENNESSEE BY 19-20Z.
SEVERAL DISCRETE...POTENTIALLY TORNADIC...SUPERCELLS ARE NOW ONGOING
NEAR/JUST AHEAD OF PRE-FRONTAL LOW-LEVEL CONFLUENT ZONE NOW
BISECTING ARKANSAS IN NORTHEAST/SOUTHWEST FASHION. THIS IS
ALONG/JUST WEST OF A 50-60 KT SOUTHERLY 850 JET AXIS...WHICH IS
PROGGED TO CONTINUE TO GRADUALLY SHIFT NORTHEASTWARD THROUGH THE
AFTERNOON HOURS...AS A 90 KT 500 MB SPEED MAXIMUM NOSES NORTHEAST OF
THE MISSOURI OZARKS. BY 19-20Z...STRONGEST LOW-LEVEL SHEAR/ LARGEST
LOW-LEVEL HODOGRAPHS ARE EXPECTED TO BE CONCENTRATED NEAR THE
LOW-LEVEL JET CORE EXTENDING ACROSS WESTERN TENNESSEE/KENTUCKY INTO
EXTREME SOUTHERN ILLINOIS/INDIANA. ADVECTION OF MID/UPPER 60S
SURFACE DEW POINTS INTO THIS REGION BY THAT TIME IS EXPECTED TO
CONTRIBUTE TO A FAVORABLE BOUNDARY LAYER ENVIRONMENT FOR TORNADIC
DEVELOPMENT...INCLUDING THE RISK FOR ISOLATED STRONG TORNADOES.
FARTHER TO THE SOUTH/WEST...INTO PARTS OF NORTHERN LOUISIANA...
WEAKENING LOW-LEVEL SHEAR AND BACKING MID/UPPER FLOW AHEAD OF THE
NEXT IMPULSE PIVOTING AROUND THE MID-LEVEL CLOSED LOW...INTO THE
SOUTHERN PLAINS...ARE EXPECTED TO CONTRIBUTE TO MORE UNCERTAIN
TORNADIC POTENTIAL. BUT...THE BOUNDARY LAYER ACROSS THE LOWER
MISSISSIPPI VALLEY WILL REMAIN VERY MOIST WITH CAPE IN EXCESS OF
2000 J/KG...IN THE PRESENCE OF DEEP LAYER SHEAR WHICH SHOULD REMAIN
SUFFICIENT FOR AT LEAST ISOLATED SUPERCELLS.
KERR.. 05/02/2008