Preliminary Forecasts
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FXUS02 KWNH 250454
PREEPD

PRELIMINARY EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1153 PM EST FRI FEB 24 2017

VALID 12Z TUE FEB 28 2017 - 12Z SAT MAR 04 2017

...OVERVIEW AND GUIDANCE PREFERENCES...

TROUGHING IS FORECAST TO TRANSITION OUT OF THE WESTERN STATES AND
INTO THE EAST NEXT WEEK AS A SURFACE FRONT EXITS THE PLAINS
TUESDAY AND THE EAST COAST THURSDAY. A TRAILING SYSTEM FROM CANADA
MAY ORGANIZE BY NEXT WEEKEND JUST NORTH OF THE BORDER. THE MODELS
AND ENSEMBLES HAVE BEEN IN GENERALLY GOOD AGREEMENT THOUGH THE GFS
HAS BEEN DISPLACED FROM THE BETTER ENSEMBLE CLUSTERING LED BY THE
ECMWF. AS SUCH, USED A BLEND OF CONTINUITY WITH THE 12Z
ECMWF/CANADIAN AND THE GEFS/ECENS MEAN FOR THE BULK OF THE
FORECAST. CONFIDENCE IS ABOUT AVERAGE. TIMING OF THE COLD FRONT
EASTWARD ON WED/THU MAY BE MODULATED BY A SFC WAVE ALONG THE FRONT
(AS SEEN IN VARIOUS RUNS OF THE GFS/ECMWF/CANADIAN OVER THE PAST
FEW DAYS), BUT LACK OF CONSISTENCY LIMITED CONFIDENCE IN A
DRASTICALLY SLOWER PACE. BY NEXT FRI/SAT, THERE REMAINS LARGE
ENSEMBLE DISAGREEMENT ON HOW THE UPSTREAM PACIFIC FLOW (OFF THE
PAC NW COAST) EVOLVES AND THE ENSEMBLE MEANS ARE BLURRING SOME
QUITE VARIED SOLUTIONS, BUT CANNOT FAVOR ONE OVER THE OTHER AS OF
YET. THIS ALSO TRANSLATES DOWNSTREAM INTO THE NORTHERN TIER AS
SEEN IN THE DIFFERENCE BETWEEN THE RECENT 18Z/12Z GFS RUNS (MUCH
STRONGER AND QUICKER SURFACE LOW) AND THE 12Z ECMWF/CANADIAN
(SLOWER AND FARTHER NORTH THAN THE ENSEMBLE MEANS).


...WEATHER HIGHLIGHTS/THREATS...

SHOWERS AND EMBEDDED HEAVIER RAIN/CONVECTION WILL PROGRESS
EASTWARD WITH THE COLD FRONT FROM THE SOUTHERN ROCKIES THROUGH THE
LOWER MISSISSIPPI VALLEY TUE-WED AND THEN INTO THE
NORTHEAST/MID-ATLANTIC LATER WED INTO THU. SNOW IS LIKELY ON THE
NW SIDE OF THE LOW FROM MN/WI THROUGH THE U.P. OF MICHIGAN IN
MARGINALLY COLD AIR. PRECIPITATION COVERAGE DECREASES BY LATER IN
THE WEEK WITH BROAD NW FLOW THROUGH MOST OF THE CONUS. WASHINGTON
STATE WOULD STAND THE BEST CHANCE FOR MODEST RAIN/SNOW (AND POINTS
NORTHWARD THROUGH COASTAL BRITISH COLUMBIA) GIVEN THE STRONG JET
SETUP. TEMPERATURES SHOULD TREND BACK TOWARD MORE TYPICAL LEVELS
IN THE EAST AFTER THE FRONT CLEARS THE COAST WHILE TEMPERATURES
SHOULD RISE BACK ABOVE AVERAGE IN THE WEST AND THEN THE PLAINS BY
NEXT FRI/SAT.


FRACASSO


$$





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