MESOSCALE DISCUSSION 2101
   NWS STORM PREDICTION CENTER NORMAN OK
   1156 PM CDT FRI SEP 02 2011
   
   AREAS AFFECTED...IA TO FAR SOUTHERN WI/NORTHERN IL
   
   CONCERNING...SEVERE THUNDERSTORM WATCH 824...
   
   VALID 030456Z - 030630Z
   
   THE SEVERE WEATHER THREAT FOR SEVERE THUNDERSTORM WATCH 824
   CONTINUES.
   
   SEVERE TSTM WATCH 824 CONTINUES UNTIL 09Z...WITH A CONTINUED THREAT
   FOR DAMAGING WINDS AND SOME SEVERE HAIL ON AN ISOLATED BASIS. A
   SEVERE THREAT COULD SPREAD EAST-NORTHEASTWARD INTO FAR SOUTHERN
   WI/NORTHERN IL OVERNIGHT...AND A WATCH MAY BE NEED TO BE CONSIDERED
   FOR THESE AREAS.
   
   TWO RELATIVELY DISTINCT CLUSTERS OF STRONG/SEVERE TSTMS CONTINUE TO
   STEADILY SPREAD EAST-NORTHEASTWARD EARLY IN THE OVERNIGHT...ONE NEAR
   THE WATERLOO AREA IN ADDITION TO ANOTHER NEAR THE DES MOINES/AMES
   VICINITIES AS OF 0445Z. IN FACT...A 51 KT WIND GUST WAS RECENTLY
   MEASURED AT WATERLOO IA. THESE STORMS WILL CONTINUE TO FAVOR A
   CORRIDOR NEAR/JUST NORTH OF A SURFACE FRONT...WHERE A FAVORABLE
   COLLOCATION OF VERTICAL SHEAR/MODERATE INSTABILITY JUST ABOVE THE
   SURFACE EXISTS. WHILE THE LONGEVITY OF THE SEVERE THREAT IS
   QUESTIONABLE GIVEN FACTORS SUCH AS INCREASING NEAR-SURFACE
   CINH...WEAK WARM ADVECTION AND EXISTING ORGANIZATION OF THESE STORMS
   MAY ALLOW AT LEAST AN ISOLATED SEVERE THREAT TO SPREAD INTO PORTIONS
   OF SOUTHERN WI/NORTHERN IL OVER THE NEXT FEW HOURS.
   
   ..GUYER.. 09/03/2011
   
   
   ATTN...WFO...LOT...MKX...DVN...ARX...DMX...
   
   LAT...LON   41339440 42069442 42449399 43109060 42868891 41688933
               41299230 41339440