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