MESOSCALE DISCUSSION 1870
   NWS STORM PREDICTION CENTER NORMAN OK
   1142 AM CDT TUE SEP 21 2010
   
   AREAS AFFECTED...NORTHERN/CENTRAL LOWER MI
   
   CONCERNING...SEVERE POTENTIAL...WATCH POSSIBLE 
   
   VALID 211642Z - 211845Z
   
   SEVERE THREAT MAY INCREASE THROUGH EARLY/MID AFTERNOON ACROSS
   NORTHERN/CENTRAL PORTIONS OF LOWER MI. DAMAGING WINDS WOULD BE THE
   PRIMARY CONCERN...BUT SEVERE HAIL/PERHAPS A TORNADO WILL BE POSSIBLE
   AS WELL.
   
   PER LATEST WATER VAPOR IMAGERY...A FAST MOVING SHORTWAVE TROUGH IS
   SPREADING EAST-NORTHEASTWARD NEAR THE U.P. OF MI VICINITY AT MIDDAY.
   IMMEDIATELY AHEAD OF THIS...IT IS CONCEIVABLE THAT LARGE SCALE
   ASCENT COUPLED WITH A HEATING/MOISTENING BOUNDARY LAYER WILL BE
   FAVORABLE FOR STRONG/SEVERE TSTM DEVELOPMENT OVER THE NEXT FEW HOURS
   ACROSS NORTHERN LOWER MI...ALTHOUGH LOW LEVEL CONVERGENCE IS
   INITIALLY MODEST OWING TO A PRE-FRONTAL BAND OF CONFLUENCE. THE 12Z
   OBSERVED RAOB FROM ALPENA MI REFLECTED AMPLE MOISTURE BENEATH
   RELATIVELY STEEP LAPSE RATES ALOFT...WITH IMPLICATIONS FOR SURFACE
   BASED TSTM DEVELOPMENT TO BECOME MORE PROBABLE AS CINH CONTINUES TO
   ERODE WITH TEMPERATURES WARMING THROUGH THE UPPER 70S/LOWER 80S F.
   GIVEN THE MAGNITUDE OF OBSERVED WIND FIELDS /50+ KT BETWEEN 1-6
   KM/...INCREASING SIGNS OF SURFACE BASED TSTM DEVELOPMENT WOULD
   LIKELY PROMPT A WATCH ISSUANCE THIS AFTERNOON.
   
   ..GUYER.. 09/21/2010
   
   
   ATTN...WFO...DTX...APX...GRR...
   
   LAT...LON   45578550 45618379 45178320 43688368 43158563 44068661
               45578550