323
FXUS02 KWBC 131812
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS HYDROMETEOROLOGICAL PREDICTION CENTER CAMP SPRINGS MD
211 PM EDT TUE OCT 13 2009
VALID 12Z FRI OCT 16 2009 - 12Z TUE OCT 20 2009
PRELIMINARY UPDATE...
THE PRELIMINARY FRONTS AND PRESSURES FOR DAYS 3 THROUGH 7 WERE
UPDATED USING THE 00Z/13 ECMWF FOR MUCH OF THE FORECAST
PERIOD...WITH A SUBSTANTIAL INCORPORATION OF ITS ATTENDANT
ENSEMBLE MEAN BY DAY 7. WHILE NONE OF THE GLOBAL NUMERICAL MODELS
HAVE SHOWN THE MOST HEARTENING CONTINUITY OVER THE LAST SEVERAL
RUNS...THE ECMWF AT LEAST RESEMBLES ITSELF FROM
YESTERDAY...PARTICULARLY ALONG THE EAST COAST WHERE THE LONGITUDE
OF CYCLOGENESIS HAS GREAT BEARING ON THE CONDITIONS OVER THE MID
ATLANTIC AND NORTHEAST DURING THE FIRST FEW DAYS. THE FLOW REGIME
IS PURE WINTER...COAST TO COAST...WITH A SPRAWLING...POLAR HIGH
BANKED ACROSS SOUTHEAST CANADA FEEDING ENOUGH COLD AIR INTO THE
CENTRAL AND NORTHERN APPALACHIANS AND THE ADJACENT HIGHER TERRAIN
TO PRODUCE SOME SNOW ON THE BACKSIDE OF THE PRECIPITATION SHIELD
THERE DAYS 3 THROUGH 5. WOULD NOT BE SURPRISED IF SOME
MOUNTAINTOP IN THE MID ATLANTIC STATES SEES A HEFTY ACCUMULATION
DURING THIS TIME. THE POSITIVE TILT OF THE LONGWAVE TROUGH OVER
THE EAST WILL PRECLUDE GULF MOISTURE RETURNING INTO THE CENTRAL
STATES...WITH ANY CLIPPER SYSTEMS HAVING TO WORK WITH LIFT ALONE
TO PRODUCE MUCH PRECIPITATION. NOW THAT THE PACIFIC FLOOD GATES
ARE OPEN...POINTS FARTHER WEST WILL SEE AN UNSETTLED THIRD WEEK OF
OCTOBER...WITH THE COASTLINE FROM 40N UP NETTING THE MOST
RAINFALL. THE SOUTHWEST WILL REMAIN REMOVED FROM THE
FRAY...TUCKED SAFELY WITHIN THE SUBTROPICAL RIDGE.
FINAL...
DESPITE THE MORE AMPLIFIED SOLUTION OF THE 12Z/13 GFS...THE NEW
GUIDANCE OVERALL SPELLS LESS OF A THREAT OF PROLONGED
PRECIPITATION OVER THE UPCOMING WEEKEND FOR THE CENTRAL
APPALACHIANS...AND HENCE...LESS OF A CHANCE OF HEAVY SNOW THERE.
THE GEM GLOBAL IS CLOSE TO THE SOLUTION WHICH INFORMED THE UPDATE
PACKAGE...WITH THE UKMET TRENDING STRONGLY TOWARD IT BY DAYS 5 AND
6 WITH ITS MUCH MORE PROGRESSIVE SOLUTION OVER THE WESTERN
ATLANTIC. STILL FEEL THAT THE WESTERN STATES ARE WELL COVERED BY
THE PRELIMINARY UPDATE.
CISCO
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