Preliminary Forecasts
Issued by NWS

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FXUS02 KWNH 040515
PREEPD

PRELIMINARY EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
114 AM EDT TUE AUG 04 2015

VALID 12Z FRI AUG 07 2015 - 12Z TUE AUG 11 2015

CONSIDERING THE RATHER COMPLEX AND UNUSUAL FLOW PATTERN EMERGING
ACROSS THE LOWER 48---THE MEDIUM RANGE FORECAST REMAINED
SURPRISINGLY STABLE---WITH RESPECT TO `TRACK-ABLE` SYNOPTIC-SCALE
WAVES AND THE LONG WAVE TROUGH CONFIGURATION ALONG BOTH COASTS OF
CANADA. THOUGHT THE 3/12Z ECENS...NAEFS AND PREVIOUS WPC
FORECAST---PROVIDED THE BEST REPRESENTATION OF THE MID-LEVEL FLOW
AND SENSIBLE WEATHER PATTERN FROM COAST TO COAST.

FOR SOME REASON---THE 3/12Z DETERMINISTIC ECMWF/GFS WERE NOT MUCH
HELP AT ALL IN THE GREAT LAKES AND NORTHEAST BEYOND DAY 3. THE
ECMWF/GFS PART WAYS---WHEN THE GFS TRACKS A SYSTEM FROM THE SOUTH
CENTRAL PLAINS THROUGH THE OHIO VALLEY---DIRECTLY INTO THE HEART
OF THE MID-LEVEL NORTHWEST FLOW. ON THE OTHER HAND---THE ECMWF
SEEMED JUST AS UNLIKELY A SURFACE SOLUTION BY EARLY 4---PHASING
MID-LEVEL ENERGY OVER THE EASTERN GREAT LAKES WITH AN INTENSE
SURFACE WAVE EMERGING LEE SIDE OF THE VIRGINIA PORTION OF THE
APPALACHIANS---ALONG THE LEADING EDGE OF THE COLD FRONT. THAT
REALLY LOOKS TOO MUCH LIKE A MID-WINTER SCENARIO...AND COULD NOT
BE USED EITHER.

IF THERE WAS A 3/12Z DETERMINISTIC SOLUTION THAT HELD TO
CONTINUITY ACROSS NORTH AMERICA---AND FOLLOWED THE ENSEMBLE
MEANS---THOUGHT IT WAS THE CANADIAN THROUGH DAY 6. THIS SOLUTION
MAINTAINS GOOD SEPARATION BETWEEN FRONTAL PASSAGES BENEATH THE
UPPER-LEVEL IN SOUTHEAST CANADA ON DAYS 3-4 ACROSS THE NORTHEAST
AND GREAT LAKES.

VOJTESAK







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