Preliminary Forecasts
Issued by NWS

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FXUS02 KWNH 260613
PREEPD

PRELIMINARY EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
212 AM EDT TUE SEP 26 2017

VALID 12Z FRI SEP 29 2017 - 12Z TUE OCT 03 2017

...OVERVIEW AND GUIDANCE EVALUATION/PREFERENCES...

PROGRESSIVE PATTERN LATER THIS WEEK WILL ATTEMPT TO RE-ESTABLISH
THE WESTERN CONUS TROUGH AND EASTERN RIDGE BY THIS WEEKEND INTO
NEXT WEEK. SURFACE COLD FRONT AND SECONDARY FRONT WILL SINK
SOUTHEASTWARD FRI-SUN WHILE ANOTHER SYSTEM MOVES THROUGH THE
NORTHWEST AND ACROSS THE PLAINS. THE MODELS/ENSEMBLES HAVE
STRUGGLED FOR SEVERAL DAYS WITH THE UPSTREAM FLOW OUT OF THE NORTH
PACIFIC, AND THE LATEST 12Z ENSEMBLES WERE MUCH THE SAME. DESPITE
THE DISAGREEMENT BETWEEN THE 12Z GEFS AND 12Z ECMWF ENSEMBLE AND
CANADIAN MEANS, THE 18Z GEFS MEAN CAME INTO BETTER AGREEMENT WITH
THE OTHER CENTER MEANS IN THE WEST BY NEXT WEEK SHOWING TROUGHING
RELOADING INTO THE WEST COAST LATE MON INTO TUE. BLEND OF THE
RECENT 12Z/18Z GFS WITH THE 12Z ECMWF (AND SOME 12Z UKMET) OFFERED
A GOOD STARTING POINT FOR THE FIRST FEW DAYS (FRI-SUN). TREND WAS
FOR A LITTLE QUICKER PROGRESSION OF THE UPPER TROUGH OUT OF THE
NORTHEAST BUT STRONGER RIDGING BEHIND IT THROUGH THE UPPER MIDWEST
INTO SOUTH CENTRAL CANADA. THIS WAS AIDED BY THE NOW DUAL UPSTREAM
TROUGHING THAT BARRELS INTO THE WEST. DETERMINISTIC MODELS HAVE
BEEN WOEFULLY INCONSISTENT BY NEXT SUN/MON, SO A TREND TOWARD THE
18Z GEFS MEAN AND 12Z ECMWF ENSEMBLE MEAN WAS WARRANTED. THE 18Z
GFS OFFERED SOME DETAIL TO THE LAST DAYS OF THE FORECAST AS THE
ECMWF SEEMED TOO DEEP WITH ITS SECOND UPPER LOW CENTERED OFF SW
OREGON BY NEXT TUE PER THE ENSEMBLE SPAGHETTI.


...WEATHER HIGHLIGHTS...

PRECIPITATION WILL BE FAVORED ALONG AND AHEAD OF THE FRONT IN THE
SOUTHEAST, PRIMARILY IN FLORIDA, BUT ALSO IN THE NORTHEAST AS THE
UPPER LOW AND SECONDARY FRONT DEPART. THE PAC NW WILL SEE BOUTS OF
RAIN AND MOUNTAIN SNOW WITH THE FIRST FRONTAL AND THEN THE UPPER
TROUGH PASSAGE FRI-SUN FOLLOWED BY THE NEXT SYSTEM MON-TUE.
ADDITIONAL RAINFALL IS LIKELY OVER WESTERN TEXAS BACK THROUGH
NM/CO AROUND THE BACKSIDE OF THE UPPER HIGH EARLY IN THE PERIOD.
TEMPERATURES WILL SETTLE BACK TO WITHIN THE MORE TYPICAL RANGE OF
LATE SEPT/EARLY OCT -- FEW, IF ANY, RECORD HIGHS/LOWS ARE
EXPECTED.


FRACASSO


$$




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