Preliminary Forecasts
Issued by NWS

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FXUS02 KWNH 270433
PREEPD

PRELIMINARY EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1232 AM EDT TUE SEP 27 2016

VALID 12Z FRI SEP 30 2016 - 12Z TUE OCT 04 2016

A BLEND OF THE 26/12Z ECENS/NAEFS AND GEFS MEANS SEEMED TO
MAINTAIN VERY GOOD CONTINUITY WITH THE PREVIOUS PACKAGE. THE DAY
SHIFT DISCUSSION DESCRIBES THINGS WELL ENOUGH. VOJTESAK

AN UPPER LEVEL CLOSED/CUTOFF LOW WILL VERY SLOWLY LIFT OUT OF THE
OHIO VALLEY LATER THIS WEEK THROUGH THE WEEKEND WHILE TROUGHING IS
REINFORCED INTO THE PACIFIC NORTHWEST. THE MIDDLE SECTION OF THE
COUNTRY WILL START DRY AND MILD BUT WILL SEE AN INCREASED CHANCE
OF RAIN LATE IN THE WEEKEND INTO EARLY NEXT WEEK.

FOR THE FIRST TIME IN ABOUT A WEEK, THE MODELS AND THEIR ENSEMBLE
MEANS HAVE NEARLY SETTLED ON A COMMON SOLUTION REGARDING THE
EVOLUTION OF A PARTICULARLY POORLY-HANDLED UPPER/CLOSED LOW IN THE
EAST LATER THIS WEEK. THERE IS AGREEMENT THAT THE CLOSED LOW WILL
COMPLETELY CUT OFF FROM THE WESTERLIES NEAR OH/KY THU/FRI AND THEN
SLOWLY LIFT NORTHWARD THIS WEEKEND. A +2 SIGMA HEIGHT ANOMALY NEAR
JAMES BAY IS FORECAST TO SLOWLY MOVE NORTHEASTWARD THROUGH THE
PERIOD WHICH FAVORS A SLOW EXODUS OF THE CLOSED LOW TO ITS SOUTH
THROUGH NEW ENGLAND AROUND NEXT MONDAY. A BLEND OF THE 06Z
GFS/GEFS AND 00Z ECMWF/ECENS MEAN OFFERED A REASONABLE STARTING
POINT FOR THE FORECAST THROUGH SUNDAY. THE 00Z ECMWF WAS SLOWEST
TO MOVE THE CLOSED LOW AWAY FROM THE GREAT LAKES COMPARED TO THE
GFS AND CANADIAN AND WOULD NOT AT ALL BE UNEXPECTED, BUT OPTED TO
USE AN ENSEMBLE BLEND GIVEN THE DISAGREEMENT IN THE WEST AS TO THE
ORIENTATION OF THE TROUGH AND UNCERTAINTY IN EMBEDDED SHORTWAVES.

WITH THE CLOSED LOW NEARLY STUCK IN THE EAST FOR SEVERAL DAYS, AN
INFLUX OF MOISTURE FROM THE ATLANTIC WILL BE CHANNELED INTO THE
MID-ATLANTIC AND NORTHEAST IN WAVES. COOLER THAN AVERAGE DAYTIME
HIGHS ARE EXPECTED WITH ABUNDANT CLOUDINESS. AS THE UPPER LOW
WEAKENS AND FILLS OVER TIME, PRECIPITATION COVERAGE WILL DECREASE
BY SUN/MON. COLD POOL ALOFT SUGGESTS LINGERING CLOUDS AROUND THE
DECAYING CIRCULATION WITH AFTERNOON HEATING. THE ENSEMBLES FOCUS
THE PRECIPITATION INITIALLY ON THE MID-ATLANTIC LATER THIS WEEK
(THU-FRI) AND THEN NORTHWARD INTO THE NORTHEAST AS THE UPPER AND
SFC SYSTEMS MOVE NORTHWARD. TAIL END OF THE FRONTAL BOUNDARY WILL
LINGER AROUND FLORIDA WHICH WILL KEEP RAIN IN THE FORECAST NEARLY
EVERY DAY FOR CENTRAL/SOUTH PORTIONS.

THE WEST WILL SEE A LEAD FRONTAL BOUNDARY LINGER THU/FRI AND THEN
PROGRESS EASTWARD THIS WEEKEND, BRINGING COOLER TEMPERATURES TO
MONTANA/WYOMING AND EVENTUALLY INTO THE HIGH PLAINS. MUCH OF THE
PACIFIC NORTHWEST INTO NORTHERN/CENTRAL CALIFORNIA AND THEN THE
GREAT BASIN WILL SEE BELOW AVERAGE TEMPERATURES AS THE TROUGH GETS
REINFORCED THIS WEEKEND. PRECIPITATION WILL SPREAD EASTWARD
THROUGH THE CENTRAL AND NORTHERN ROCKIES AS THE FRONT MOVES SOUTH
AND EAST.

FRACASSO

$$





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