Midwest Chasing

...SEVERE THUNDERSTORMS EXPECTED OVER PARTS OF THE MIDWEST THIS  
AFTERNOON AND TONIGHT...  

THE NWS STORM PREDICTION CENTER IN NORMAN OK IS FORECASTING THE  
DEVELOPMENT OF WIDESPREAD DAMAGING WINDS AND LARGE HAIL OVER PARTS  
OF THE MIDWEST THIS AFTERNOON AND TONIGHT.  

THE AREAS MOST LIKELY TO EXPERIENCE THIS ACTIVITY INCLUDE  

       MUCH OF IOWA  
       NORTHERN ILLINOIS  
       NORTHEAST NEBRASKA  
       SOUTHEAST SOUTH DAKOTA  

SURROUNDING THE MODERATE RISK AREA...THERE IS A SLIGHT RISK OF  
SEVERE THUNDERSTORMS FROM SOUTHEAST MONTANA...ACROSS THE MID  
MISSISSIPPI VALLEY...INTO PARTS OF OHIO AND KENTUCKY.  

A VERY MOIST AND EXTREMELY UNSTABLE AIR MASS IS FORECAST TO DEVELOP  
THIS AFTERNOON ALONG AND SOUTH OF A SURFACE BOUNDARY EXTENDING FROM  
PARTS OF SOUTH DAKOTA AND NEBRASKA...ACROSS IOWA AND INTO NORTHERN  
IL.  AN UPPER LEVEL IMPULSE WILL APPROACH THE AREA FROM THE WEST BY  
LATE AFTERNOON...LEADING TO THE DEVELOPMENT OF SCATTERED  
THUNDERSTORMS ALONG THE BOUNDARY.  FAVORABLE WIND FIELDS  
ALOFT...EXTREME INSTABILITY...AND APPROACHING UPPER SYSTEM WILL  
PROMOTE THE DEVELOPMENT OF ONE OR MORE LARGE CLUSTERS OF SEVERE  
THUNDERSTORMS.  THESE CLUSTERS WILL MOVE RAPIDLY EASTWARD ALONG THE  
BOUNDARY WITH A RISK OF WIDESPREAD DAMAGING WINDS AND LARGE HAIL.