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Mesoscale Discussion 249
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   MESOSCALE DISCUSSION 0249
   NWS STORM PREDICTION CENTER NORMAN OK
   0617 AM CDT MON MAR 21 2016

   AREAS AFFECTED...COASTAL AND INLAND PORTIONS OF SOUTHERN TO DOWNEAST
   MAINE

   CONCERNING...HEAVY SNOW 

   VALID 211117Z - 211600Z

   CORRECTED FOR TYPO IN FIRST SENTENCE OF THE DISCUSSION.

   SUMMARY...MODERATE TO HEAVY SNOWFALL RATES /WITH GREATEST RATES
   AROUND 1 INCH PER HOUR/ WITHIN ONE OR MORE BANDS WILL DEVELOP ACROSS
   THE WESTERN PORTION OF THE DISCUSSION AREA THROUGH 12Z AND INTO
   DOWNEAST MAINE BY 15Z.  ONCE SNOWFALL BEGINS...IT IS EXPECTED TO
   PERSIST THROUGH THE MORNING AND SHOULD LINGER THE LONGEST INTO THE
   EARLY AFTERNOON ACROSS PARTS OF DOWNEAST MAINE...WITH A CONTINUATION
   OF MODERATE TO HEAVY SNOWFALL RATES.

   DISCUSSION...TRENDS IN MOSAIC RADAR IMAGERY AND SURFACE OBSERVATIONS
   SINCE 10Z INDICATED TWO BANDS OF MODERATE-HEAVY SNOWFALL RATES HAVE
   TRANSITIONED INTO A SINGLE...PRIMARY BAND EXTENDING FROM CENTRAL MA
   THROUGH SOUTHEAST NH TO SOUTHWEST AND SOUTH-CENTRAL MAINE.  SNOWFALL
   RATES UP TO AROUND 1 INCH PER HOUR HAVE OCCURRED THUS FAR WITHIN THE
   BANDS.  

   THIS PRIMARY BAND IS LOCATED IN THE WEST/NORTHWEST PERIPHERY OF A
   DEEPENING LOW PRESSURE AREA WHICH WAS TRACKING TO THE NORTHEAST FROM
   EAST/SOUTHEAST OF 40N/70W EARLY THIS MORNING AND SHOULD REACH
   WESTERN PART OF NOVA SCOTIA BY EARLY AFTERNOON.  THE DEEPENING
   SURFACE LOW IS IN RESPONSE TO AN INCREASE IN UPWARD VERTICAL MOTION
   AS 1/ A SHORTWAVE TROUGH TAKES ON MORE OF A NEGATIVE TILT TODAY
   TRACKING THROUGH NEW ENGLAND AND 2/ THE DISCUSSION AREA BECOMES
   JUXTAPOSED BENEATH COUPLED STRONG SWLY MID- TO UPPER-LEVEL JETS. 
   GIVEN THE AFOREMENTIONED AND ALREADY FORMED BAND WITH ONGOING
   MODERATE TO HEAVY SNOWFALL RATES...THE 06Z NAM APPEARS TO BE THE
   BETTER MODEL WHICH SUGGESTED FAVORABLE MIDLEVEL /600-MB AND 700-MB/
   FRONTOGENETICAL FORCING WILL PERSIST AND SPREAD ACROSS SOUTHERN AND
   DOWNEAST MAINE THROUGH AT LEAST THIS MORNING.  THUS...ONE OR MORE
   BANDS OF SNOW WILL BE LIKELY.  THIS INCREASING ASCENT WILL CONTINUE
   TO OCCUR WITHIN THE DENDRITIC GROWTH ZONE SUPPORTIVE OF THE HEAVIER
   SNOWFALL RATES.  AS THE SURFACE LOW MOVES CLOSER TO NOVA SCOTIA...
   THE ORIENTATION OF THE BANDS BEING SW-NE IS EXPECTED TO SHIFT TO
   SSW-NNE ACROSS THE DISCUSSION AREA...AS THIS REGION BECOMES
   INFLUENCED MORE FROM THE NORTHWEST PERIPHERY OF THIS STORM SYSTEM.

   ..PETERS.. 03/21/2016


   ATTN...WFO...CAR...GYX...

   LAT...LON   43656991 43127073 43467094 43977038 44666943 45526798
               45676757 45126692 44786712 44276797 43866939 43656991 

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Page last modified: March 21, 2016
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