MESOSCALE DISCUSSION 0116
   NWS STORM PREDICTION CENTER NORMAN OK
   0641 AM CST SAT JAN 22 2005
   
   AREAS AFFECTED...LOWER MI/NRN IND/PA/WRN NY/MD/NJ/DE/NRN VA/WV
   
   CONCERNING...HEAVY SNOW 
   
   VALID 221241Z - 221845Z
   
   HEAVY SNOW WILL CONTINUE/SPREAD FROM THE LOWER PENINSULA OF MI
   ACROSS THE OH VALLEY AND MID ATLANTIC THIS MORNING...WITH HOURLY
   RATES 1-2"/HR WITH LOCALLY 3"/HR POSSIBLE. IN ADDITION TO THE HEAVY
   SNOW...A MIX OF FREEZING RAIN/SLEET WILL OCCUR ROUGHLY SOUTH OF
   PITTSBURGH TO COLUMBUS TO DAYTON.
   
   WATER VAPOR IMAGERY LOOPS SHOW TWO DISTINCT UPPER CIRCULATION
   CENTERS...WITH THE MAIN FORCING FOR LOW LEVEL CYCLOGENESIS FOCUSED
   OVER THE OH VALLEY. SATELLITE IMAGERY SUGGESTS THAT THE NRN CYCLONIC
   CENTER NOW ENTERING CNTRL IL WILL BECOME DOMINANT...WITH A
   "DUMBBELLING" EFFECT EXPECTED TO OCCUR AS THE SRN CIRCULATION OVER
   NRN IND ROTATES CYCLONICALLY AROUND IT. 
   
   SEVERAL FACTORS WILL COMBINE TODAY TO PRODUCE HEAVY SNOW OVER THE
   MID ATLANTIC INCLUDING THE ENHANCED UPPER DIVERGENCE ASSOCIATED WITH
   THE EXIT REGION OF THE IL JETSTREAK...WARM AIR ADVECTION/ISENTROPIC
   LIFT ON THE NOSE OF A 60 KT LOW LEVEL JET...AND STRONG PVA
   ASSOCIATED WITH STRONG HEIGHT FALLS / 240 METER FALLS / BY 00Z.
   
   IN THE SHORTER TERM...HEAVY SNOW WILL BE FOCUSED ACROSS SRN LOWER MI
   AND NRN OH. LONGER RADAR LOOPS SUGGEST DEFORMATION ZONE WILL LIKELY
   PIVOT TO A MORE WSW/ENE ORIENTATION IN RESPONSE TO DIGGING UPSTREAM
   WAVE. THIS WILL KEEP AREAS LIKE DETROIT...ANN ARBOR AND LANSING IN
   AN AXIS OF HEAVY SNOW FOR AN EXTENDED TIME. 
   
   FARTHER SOUTH IN WAA ZONE...FZRA WILL BE DEVELOPING ESPECIALLY SOUTH
   OF A DAYTON OH WHEELING WV TO PIT LINE. FZRA/FZDZ ARE BEING REPORTED
   FROM CVG/LHQ/CKB...AND WITH CONTINUING WAA AND SUBFREEZING SFC
   TEMPS...POTENTIAL FOR FZRA EXISTS.
   
   FINALLY...WAA PRECIPITATION HAS ALREADY OVERSPREAD PA/MD WITH
   PRECIPITATION OCCURRING MAINLY ALOFT. POINT FORECAST SOUNDINGS
   SUGGEST SNOW BEGINNING BETWEEN 12-14Z ACROSS MD/ERN PA...AND ONCE
   SNOW STARTS...AN EXTENDED PERIOD OF 8-12 HOURS OF MOD/HEAVY SNOW IS
   LIKELY GIVEN STRONG DYNAMICS AND FAVORABLE DENDRITIC GROWTH ZONE.
   ENOUGH CONVECTIVE INSTABILITY EXISTS...GIVEN RECENT LIGHTNING
   OBSERVED OVER OH...THAT SNOWFALL RATES MAY APPROACH THE 2-3"/HR
   RANGE BY MID MORNING INTO AFTERNOON.
   
   ..TAYLOR.. 01/22/2005
   
   
   ...NOTICE...
   SPC WINTER WEATHER MESOSCALE DISCUSSIONS WILL BE ISSUED ON A 
   SCHEDULED BASIS...FOUR TIMES A DAY...BETWEEN 00-01 UTC...
   06-07 UTC...12-13 UTC...AND 18-19 UTC AS SIGNIFICANT SHORT
   RANGE WINTER WEATHER EVENTS UNFOLD.  THIS SCHEDULE WILL BE
   USED FROM DECEMBER 1 THROUGH FEBRUARY 28.
   
   ATTN...WFO...OKX...ALY...PHI...BGM...AKQ...BUF...CTP...LWX...PBZ...RLX...CLE...ILN...DTX...IWX...GRR...IND...LOT...
   
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