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MESOSCALE DISCUSSION 0556
NWS STORM PREDICTION CENTER NORMAN OK
0742 PM CDT FRI APR 24 2009
AREAS AFFECTED...SWRN/SRN TO NERN IA...FAR SERN MN INTO MUCH OF
CENTRAL/NERN WI
CONCERNING...SEVERE THUNDERSTORM WATCH 180...
VALID 250042Z - 250145Z
THE SEVERE WEATHER THREAT FOR SEVERE THUNDERSTORM WATCH 180
CONTINUES.
00Z SURFACE ANALYSIS INDICATED AN AREA OF LOW PRESSURE LOCATED IN
CENTRAL WI WITH A COLD FRONT TRAILING SWWD THROUGH NERN TO SWRN IA
TO FAR SERN NEB. MEANWHILE...A BOUNDARY EXTENDED NEWD FROM THE
SURFACE LOW INTO THE CENTRAL PART OF THE U.P. OF MI.
...IA...
STRONG TO SEVERE TSTMS WILL CONTINUE TO DEVELOP ALONG THE COLD FRONT
IN IA...WITH DOWNSTREAM MODERATELY UNSTABLE AIR MASS ACROSS
CENTRAL/ERN IA CONDUCIVE FOR ACTIVITY TO PROGRESS EWD AND REMAIN
SEVERE. TSTMS LOCATED ACROSS SWRN IA MAY MOVE EAST OF THE SRN
PORTION OF WW 180 BY 01Z...WITH A LOCAL WFO AREAL EXTENSION
POSSIBLE. EFFECTIVE BULK SHEAR 35-40 KT WITH VECTORS ORIENTED
PARALLEL TO THE COLD FRONT WILL CONTINUE TO FAVOR A MORE LINEAR
STORM MODE.
...SERN MN INTO CENTRAL/NERN WI...
EFFECTIVE BULK SHEAR /35-40 KT/ WITH VECTORS CROSSING THE FRONT AT
MORE OF AN ANGLE THAN FARTHER SW INTO IA SHOULD TEND TO FAVOR AN
ADDITIONAL POTENTIAL FOR ORGANIZED DISCRETE STORMS ACROSS WI THIS
EVENING. 40-50 KT SWLY LLJ EXTENDING INTO UPPER GREAT LAKES REGION
WITH VAD WINDS SHOWING LOW LEVEL DIRECTIONAL SHEAR RESULTING IN
200-300 M2/S2 OF EFFECTIVE SRH. ALTHOUGH THIS WOULD BE SUFFICIENT
FOR A TORNADO THREAT...INCREASING SURFACE BASED INHIBITION WILL
RESULT IN A DECREASING TREND FOR SURFACE BASED PARCELS...AND THUS
LIMIT THE OVERALL TORNADO THREAT.
...NWRN WI INTO WRN U.P. OF MI...
ELEVATED TSTMS HAVE INCREASED IN COVERAGE AND INTENSITY SINCE 00Z
PER REGIONAL RADARS AND LIGHTNING DATA. THIS ACTIVITY IS LOCATED IN
THE POST FRONTAL ENVIRONMENT AND MAY BE SUPPORTED BY ASCENT
SPREADING EWD AHEAD OF THE NRN PLAINS/CENTRAL CANADA POSITIVE TILTED
TROUGH. GIVEN WEAK INSTABILITY AND EFFECTIVE SHEAR OF 20-30 KT...A
FEW STRONGER STORMS COULD PRODUCE AN ISOLATED HAIL THREAT...WITH
ACTIVITY EXPECTED TO MOVE INTO THE WRN PART OF THE U.P. OF MI.
..PETERS.. 04/25/2009
ATTN...WFO...MQT...GRB...MKX...DVN...DLH...ARX...MPX...DMX...
EAX...OAX...
LAT...LON 40809589 42149405 43299265 44369163 44899119 45559214
45959202 46689109 46948979 46788870 46468792 45768775
44288897 42379127 41329268 40489385 40329432 40809589
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