Preliminary Forecasts
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FXUS02 KWNH 300555
PREEPD

PRELIMINARY EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
154 AM EDT FRI SEP 30 2016

VALID 12Z MON OCT 03 2016 - 12Z FRI OCT 07 2016

...OVERVIEW...

A COLD FRONT WILL WORK ITS WAY ACROSS THE COUNTRY NEXT WEEK OUT OF
THE ROCKIES AND THROUGH THE PLAINS TOWARD THE APPALACHIANS. A
LINGERING COLD FRONT WILL LIE OFFSHORE THE SOUTHEAST STATES AND
THE NATIONAL HURRICANE CENTER FORECASTS HURRICANE MATTHEW TO BE
MOVING NORTHWARD THROUGH THE BAHAMAS LATE TUESDAY.


...GUIDANCE PREFERENCES AND UNCERTAINTY ASSESSMENT...

LARGE SCALE PATTERN REMAINS RELATIVELY WELL-FORECAST FOR NOW, WITH
WEAKENING TROUGHING IN THE WEST AND RIDGING IN SOUTHEASTERN CANADA
WITH A SLOWLY EXITING UPPER LOW MOVING THROUGH NEW ENGLAND.
FARTHER UPSTREAM, THE PACIFIC IS IN A STATE OF FLUX AS THE MODELS
DISAGREE ON HOW TO HANDLE A LEAD SYSTEM EXITING NORTHERN JAPAN AT
THE START OF THE MEDIUM RANGE PERIOD AHEAD OF RECURVING WHAT IS
FORECAST TO BE TYPHOON CHABA OVER SE JAPAN EARLY NEXT WEEK. TREND
IN THE ENSEMBLES HAS BEEN TOWARD LESS RIDGING OFFSHORE THE PAC NW
ON WEDNESDAY SO THAT THE IMMEDIATE RIDGE DOWNSTREAM OF EX-CHABA
CAN BUILD INTO ALASKA. STRENGTH/EVOLUTION OF THE SFC LOW IN THE
PLAINS MIDWEEK REMAINS A QUESTION. IN ADDITION, HOW QUICKLY THE
UPPER LOW WEAKENS AND MOVES INTO THE NW ATLANTIC IS STILL IN
QUESTION, WHICH INFLUENCES THE RIDGE TO ITS SOUTHEAST AND THE
FORWARD SPEED OF MATTHEW IN THE BAHAMAS. BY NEXT THU/FRI THE
ENSEMBLE SPREAD WITH MATTHEW REMAINS RATHER LARGE - 1500 MILES
ACROSS FROM SW TO NE (GULF OF MEXICO TO S OF NOVA SCOTIA).
EXTRAPOLATED POSITION FROM THE 03Z NHC POINTS ALONG WITH
CONTINUITY FROM DAY SHIFT NHC/WPC COORDINATION TAKES MATTHEW
NORTHWARD THEN EAST OF NORTH OFF CAPE HATTERAS BY NEXT THU/FRI.
00Z GFS IS CLOSEST TO THIS SOLUTION.

GIVEN THE UNCERTAINTY, A BLEND OF THE 18Z GEFS MEAN AND 12Z ECMWF
ENSEMBLE MEAN OFFERED A GOOD STARTING POINT THAT STAYED RATHER
CLOSE TO CONTINUITY. OFF THE SOUTHEAST, THE DEARTH OF ENSEMBLE
MEMBERS NEAR THE PREFERRED TRACK OF MATTHEW MADE FOR SOME CREATIVE
ISOBARIC MANIPULATION.


...WEATHER HIGHLIGHTS...

SHOWERS WILL SLOWLY EXIT THE NORTHEAST AS THE UPPER LOW WEAKENS
AND DRIFTS EASTWARD - FINALLY. A DRIER AND MILDER AIRMASS WILL
BECOME DOMINANT, THOUGH NORTHEAST FLOW FROM SFC HIGH PRESSURE OVER
NOVA SCOTIA WILL KEEP TEMPERATURES A BIT BELOW AVERAGE EAST OF THE
APPALACHIANS. AHEAD OF THE FRONT IN THE PLAINS, TEMPERATURES WILL
RISE TO 5-15 DEGREES F ABOVE AVERAGE (70S AND LOW 80S IN THE
NORTHERN PLAINS) EARLY IN THE WEEK. BEHIND THE FRONT, TEMPERATURES
WILL BE BELOW AVERAGE BY ABOUT 5-15 DEGREES (WIDESPREAD 50S WITH
40S AT HIGHER ELEVATIONS).

SHOWERS AND STORMS WILL FOCUS ALONG AND AHEAD OF THE MAIN FRONT
AND AROUND THE SFC LOW PRESSURE MOVING OUT OF WYOMING THROUGH THE
DAKOTAS. SYSTEM HAS THE POTENTIAL TO WRAP UP MORE THAN INDICATED
WHICH MAY ENHANCE PRECIPITATION ON THE NW SIDE FROM E MT INTO
ND/SD. A COUPLE WEAKER FRONTS WILL BRING PRECIP TO WA/OR AS WELL.

TO THE EAST, FRONT MAY LOSE MUCH OF ITS PRECIP SHIELD AS THE UPPER
SUPPORT LIFTS INTO CANADA. AND UNCERTAINTY WITH THE TRACK OF
MATTHEW SUPPORTS AT LEAST A CHANCE OF RAIN ALONG THE SE COAST FROM
FL TO NC AND SE VA WED THRU FRI FROM S TO N.


FRACASSO

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