Prognostic Meteorological Discussion
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000
FXUS02 KWBC 241628
PMDEPD

EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1227 PM EDT SAT SEP 24 2016

VALID 12Z TUE SEP 27 2016 - 12Z SAT OCT 01 2016

...OVERVIEW...

FRONTAL SYSTEM WILL SLOWLY EXIT AWAY FROM THE EAST COAST MIDWEEK
BUT THE MODELS VARY ON HOW QUICKLY (OR SLOWLY) THAT WILL OCCUR.
ANOTHER FRONT WILL LINGER IN THE PACIFIC NORTHWEST UNTIL
ADDITIONAL ENERGY PUSHES INTO THE REGION.


...MODEL PREFERENCES AND ASSESSMENT....

THE EVOLVING UPPER LOW IN THE GREAT LAKES EARLY NEXT WEEK IS STILL
NOT YET WELL-HANDLED BY THE MODELS OR EVEN ENSEMBLES, ESPECIALLY
AFTER NEXT WEDNESDAY. A SOMEWHAT COMPLEX UPPER PATTERN OVER
NORTHERN CANADA AND THE NORTH ATLANTIC MAY HELP EITHER KEEP THE
FLOW PROGRESSIVE THROUGH THE NORTHEAST OR ALLOW THEM TO BECOME
CUTOFF FROM THE MAIN WESTERLIES. THE MODELS/ENSEMBLES ARE NEARLY
SPLIT ON EITHER IDEA (WITH MANY SOLUTIONS IN BETWEEN) BUT THE
RECENT 00Z ENSEMBLES GENERALLY ALLOW THE CLOSED LOW TO MOVE MORE
SLOWLY THROUGH THE NORTHEASTERN CONUS THAN DID THE 12Z/23 MEMBERS.
THE 00Z ECMWF/UKMET REPRESENT THE SLOWEST SOLUTIONS WITH A CLOSED
LOW IN THE CENTRAL/SOUTHERN APPALACHIANS  WHILE THE CANADIAN
REPRESENTS THE QUICKEST. THE 00Z/06Z GFS RUNS WERE IN BETWEEN AND
REPRESENTED A GOOD COMPROMISE NEAR THE ENSEMBLE MEANS` TROUGH AXES
(DILUTED AMPLITUDE DUE TO THE SPREAD IN MEMBERS FROM SW TO NE).
USED THE 00Z GFS WITH THE 00Z GEFS/ECMWF ENSEMBLE MEAN AS THE BASE
FOR THE FORECAST PAST NEXT WEDNESDAY.

IN THE WEST, LEAD BOUNDARY SHOULD MAKE LITTLE PROGRESS EASTWARD AS
SW FLOW ALIGNS WITH THE SURFACE FRONT ACROSS OREGON INTO WESTERN
MONTANA TUE-WED. ONCE ADDITIONAL HEIGHT FALLS DIG SOUTHWARD OUT OF
THE GULF OF ALASKA NEXT WEEK (WITH A WEAK SURFACE REFLECTION) THEN
THE FRONT MAY MOVE EASTWARD THROUGH CENTRAL MONTANA/IDAHO. TO THE
SOUTH, THE SOUTHERN EXTENSION OF THE NORTHERN STREAM UPPER LOW
WILL ROTATE THROUGH THE DESERT SOUTHWEST MIDWEEK BEFORE GETTING
SUCKED BACK UP INTO THE SW FLOW OVER THE GREAT BASIN AROUND
THURSDAY.


...WEATHER HIGHLIGHTS...

ASSUMING THE COLD FRONT AND UPPER LOW REMAIN PROGRESSIVE ENOUGH IN
THE EAST, COLD FRONT SHOULD PUSH OFFSHORE THE
NORTHEAST/MID-ATLANTIC LATE TUESDAY INTO WEDNESDAY. THIS WOULD
BRING IN A DRIER AIRMASS TO THE MID-ATLANTIC/SOUTHEAST WED-THU BUT
THE POSSIBILITY EXISTS FOR A MUCH SLOWER EXODUS (A LA THE
ECMWF/UKMET) WHICH WOULD MEAN MORE CLOUDS/SHOWERS AS THE UPPER LOW
PASSES OVERHEAD. TEMPERATURES SHOULD BE NEAR AVERAGE IN THE EAST.

TO THE WEST, UPPER TROUGH AND ONSHORE FLOW WILL MEAN COOLER THAN
AVERAGE DAYTIME HIGHS BUT MILDER THAN AVERAGE OVERNIGHT LOWS ALONG
AND WEST OF THE DIVIDE IN MT/WY. ABOVE AVERAGE TEMPERATURES ARE
EXPECTED AHEAD OF THE COLD FRONT GENERALLY EAST OF THE DIVIDE AND
SOUTH OF THE FRONT INTO NORTHERN NEVADA/CALIFORNIA. UPPER LOW
ROTATING OUT OF THE NORTHERN BAJA MAY SPARK SOME SHOWERS/STORMS IN
THE MOUNTAINS OF INTERIOR SOUTHERN CALIFORNIA/NEVADA AND
ARIZONA/UTAH MIDWEEK.


FRACASSO

$$





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