MESOSCALE DISCUSSION 2272
   NWS STORM PREDICTION CENTER NORMAN OK
   0653 AM CST SAT DEC 29 2007
   
   AREAS AFFECTED...PORTIONS OF ME
   
   CONCERNING...HEAVY SNOW 
   
   VALID 291253Z - 291900Z
   
   EMBEDDED POCKETS OF LOCALLY HEAVY SNOWFALL WITH RATES APPROACHING 1
   INCH PER HOUR WILL EXIST WITHIN LARGER PRECIPITATION SHIELD THIS
   MORNING.  A RAPID DECREASE IN SNOWFALL RATES SHOULD THEN OCCUR FROM
   W-E ACROSS DISCUSSION AREA THROUGH 18Z.
   
   LOWER BRANCH OF INDIRECT THERMAL CIRCULATION ATTENDANT TO EXIT
   REGION OF STRONG UPPER LEVEL JET STREAK PROPAGATING THROUGH THE OH
   VALLEY INTO NERN STATES IS MANIFEST IN 40-60 KT LLJ THIS MORNING
   FROM THE MID ATLANTIC COAST NWD INTO NEW ENGLAND.  DESTABILIZATION
   AND FORCING FOR LARGE-SCALE ASCENT ARISING FROM STRONG THERMAL AND
   MOISTURE ADVECTIONS ALONG THIS LLJ AXIS ARE CONTRIBUTING TO LARGE 
   PRECIPITATION SHIELD EXTENDING FROM NH EWD ACROSS ME AS OF 1215Z. 
   SURFACE OBSERVATIONS INDICATE THAT MOST PRECIPITATION IS FALLING AS
   SNOW EXCEPT FOR THE COAST OF ME WHERE TEMPERATURES ARE ABOVE
   FREEZING.
   
   LATEST SHORT TERM MODEL GUIDANCE SUGGESTS THAT WAA/ISENTROPIC ASCENT
   WILL REMAIN THE PRIMARY FORCING MECHANISM ALONG EWD MIGRATING LLJ
   AXIS.  HOWEVER...RESPONSE TO SFC-925 FRONTOGENESIS ALONG AND N OF
   COASTAL FRONT MAY RESULT IN MORE INTENSE FORCING ON THE
   MESOSCALE...POSSIBLY SUPPORTING E-W ORIENTED BANDING OF HEAVIER
   SNOWFALL ACROSS PARTS OF CNTRL ME.  THIS FORCING WILL BE ACTING ON A
   RATHER FAVORABLE THERMODYNAMIC ENVIRONMENT /REF 12Z GYX SOUNDING/
   WITH AN ISOTHERMAL LAYER FROM 820-700 MB...AND SATURATED CONDITIONS
   PRESENT THROUGH THAT PORTION OF TEMPERATURE PROFILE FAVORING ICE
   CRYSTAL GROWTH THROUGH AGGREGATION.
   
   A RATHER RAPID CESSATION IN HIGHER PRECIPITATION RATES WILL OCCUR
   FROM W-E ACROSS DISCUSSION AREA THIS MORNING WITH THE GREATEST
   POTENTIAL FOR MORE PERSISTENT...HEAVY SNOW EXISTING FROM NEAR OR N
   OF BGR TO THE CANADIAN BORDER NEAR AND S OF HUL.
   
   ..MEAD.. 12/29/2007
   
   
   ...NOTICE...
   SPC WINTER WEATHER MESOSCALE DISCUSSIONS WILL BE ISSUED ON A
   SCHEDULED BASIS FROM DECEMBER 1 THROUGH FEBRUARY 28...FOUR
   TIMES A DAY...AROUND 00 UTC...06 UTC...12 UTC...AND 18 UTC
   FOR SIGNIFICANT SHORT RANGE WINTER WEATHER EVENTS.
   
   ATTN...WFO...CAR...GYX...
   
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