Prognostic Meteorological Discussion
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FXAK02 KWNH 211918
PMDAK

ALASKA EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
318 PM EDT SAT OCT 21 2017

VALID 12Z WED OCT 25 2017 - 12Z SUN OCT 29 2017

THE EXTRATROPICAL TRANSITION OF SUPER TYPHOON CONTINUES TO
INFLUENCE THE MEDIUM RANGE FORECAST OVER ALASKA. THOUGH OVER THE
PAST FEW DAYS THE MORE STABLE ENSEMBLES HAVE LARGELY AGREED WITH
EACH OTHER (GEFS AND ECMWF EPS SPECIFICALLY), DAY TO DAY (OR CYCLE
TO CYCLE) CHANGES REMAIN. NEVERTHELESS, AN EMPHASIS ON SMALLER
DAILY CHANGES SEEMED PRUDENT AND CONTINUED TO RELY ON THE ENSEMBLE
CONSENSUS WITH DETAILS ADDED FROM CLOSELY CLUSTERED DETERMINISTIC
MODELS. THE 12Z GFS AND 00Z ECMWF WERE NEAR THEIR ENSEMBLE MEANS
TO START THE FORECAST AS THE DEEP LAN-INFUSED SYSTEM TRAVERSES THE
BERING SEA WEDNESDAY. TREND HAS BEEN WAFFLING BETWEEN SLOWER AND
FASTER, WITH THE LATEST CYCLE AGAIN SLOWER, LIKELY DUE TO THE
PROLONGED EXISTENCE OF THE PARENT LOW THAT MAY SKIRT JUST NORTH OF
THE ALEUTIANS AS THE OCCLUSION PUSHES TOWARD THE BERING STRAIT AND
INTO W ALASKA WED/THU. TRIPLE POINT SHOULD STILL BECOME THE NEW
PARENT LOW TO THE OLD FRONT CONTINUING THROUGH THE GULF NEXT
THU/FRI BUT THEN LIKELY WEAKENED BY THE END OF THE PERIOD BY
BUILDING RIDGING OVER THE WESTERN COAST OF CANADA. NEXT SYSTEM
SHOULD ENTER THE BERING ON THURSDAY BUT ITS EVOLUTION IS QUITE
UNCLEAR WITH ADDED UNCERTAINTY FROM UPSTREAM IN THE PACIFIC AS
WELL AS NORTH OF HAWAI`I. ENSEMBLES INDICATE A WAVE MAY RIDE
NORTHWARD ALONG THE FRONT ACROSS THE WESTERN OR CENTRAL ALEUTIANS
WHICH AT LEAST MAKES SENSE GIVEN THE EXPECTED DOWNSTREAM RIDGING
TO BUILD.

RELATIVELY MILD AIR SHOULD BE PUMPED INTO W/SW ALASKA AS THE
OCCLUSION COMES ASHORE. PRECIPITATION WILL OVERTAKE MOST OF THE
STATE OUTSIDE THE NORTHEAST 1/3 OR SO, FOCUSED ESPECIALLY ALONG
THE SOUTHCENTRAL COAST INTO THE PANHANDLE WHERE SEVERAL INCHES OF
RAIN (LOCAL MAXIMA OVER TEN INCHES) ARE EXPECTED.


FRACASSO


$$




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