MESOSCALE DISCUSSION 0756
NWS STORM PREDICTION CENTER NORMAN OK
0328 PM CDT THU MAY 01 2008
AREAS AFFECTED...PARTS OF ERN NEB/WRN IA INTO SE SD/SW MN
CONCERNING...SEVERE POTENTIAL...WATCH LIKELY
VALID 012028Z - 012200Z
IT APPEARS PROBABLE THAT A TORNADO WATCH WILL BE NEEDED AT SOME
POINT LATE THIS AFTERNOON OR EARLY EVENING...POSSIBLY AS EARLY AS
THE 21-22Z TIME FRAME.
A GRADUAL MOISTENING OF LOWER LEVELS CONTINUES IN A NARROW TONGUE
ACROSS THE EAST CENTRAL PLAINS/MID MISSOURI VALLEY...INTO THE
VICINITY OF A DEEP SURFACE CYCLONE NEAR NORFOLK NEB. THIS IS NEARLY
COINCIDENT WITH A CORRIDOR OF STRONGER SURFACE HEATING AHEAD OF AN
INITIAL WEAK COOL SURGE TO THE SOUTH OF THE SURFACE LOW.
AND...LATEST RUC GUIDANCE SUGGESTS THAT INHIBITION FOR BOUNDARY
LAYER PARCELS IS BECOMING NEGLIGIBLE ACROSS NORTHEAST
NEBRASKA...WHERE DEEPENING CUMULUS/TOWERING CU ARE ALREADY EVIDENT.
ALTHOUGH STRONGER FORCING ASSOCIATED WITH AN INITIAL IMPULSE
ROTATING AROUND THE CENTRAL ROCKIES MID-LEVEL CIRCULATION CENTER
APPEARS TO BE LIFTING NORTH OF REGION...AND FORCING WITH THE NEXT
IMPULSE MAY NOT INCREASE UNTIL NEAR/SHORTLY AFTER 02/00Z...THE
INITIATION OF STORMS BENEATH DIFLUENT CYCLONIC MID-LEVEL FLOW
APPEARS POSSIBLE AS EARLY AS 01/22-23Z. AS THIS OCCURS...MIXED
LAYER CAPE UP TO AROUND 2000 J/KG...IN THE PRESENCE OF MODERATE TO
STRONG DEEP LAYER NEAR THE POLAR JET AXIS...WILL BE SUPPORTIVE OF
SUPERCELLS. SIZABLE CLOCKWISE CURVED LOW-LEVEL HODOGRAPHS AND
AMBIENT VERTICAL VORTICITY WILL BE FAVORABLE FOR TORNADOES...IN
ADDITION TO THE RISK FOR LARGE HAIL/LOCALIZED DAMAGING WIND GUSTS.
..KERR.. 05/01/2008
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