Prognostic Meteorological Discussion
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FXAK02 KWNH 251908
PMDAK

ALASKA EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
308 PM EDT TUE JUL 25 2017

VALID 12Z SAT JUL 29 2017 - 12Z WED AUG 02 2017

LARGE SCALE FLOW REMAINS IN RELATIVELY GOOD ENSEMBLE AGREEMENT
THROUGH THE MEDIUM RANGE (SAT-WED). THIS KEEPS A REINFORCED UPPER
LOW PINNED TO THE GULF OF ALASKA WITH A STRONG UPPER HIGH SW AND
THEN S OF THE ALEUTIANS. TREND HAS BEEN TOWARD A BETTER-DEFINED
SYSTEM IN THE SE GULF TO START THE PERIOD THAT WILL PUSH PAST THE
PANHANDLE BY SUNDAY. TRAILING SYSTEM TIED TO A WEAK SHORTWAVE
SHOULD ROTATE AROUND THE UPPER LOW SUN/MON AND PUSH TOWARD THE
PANHANDLE NEXT TUE. THIS MAY BE FOLLOWED BY A SUBSEQUENT SYSTEM
OUT OF THE FAR NW BERING SEA AS HEIGHTS FALL IN RESPONSE TO A
SHIFT SOUTHWARD AND EASTWARD OF THE UPPER HIGH/RIDGE IN THE N
PACIFIC. THE ECMWF/ECENS MEAN AND GFS RUNS WERE QUICKER TO LOWER
HEIGHTS IN THE BERING THAN THE GEFS MEMBERS, SO USED THAT LARGER
CLUSTER AS THE BASE TO THE FORECAST. 00Z GFS WAS CLOSE TO THE 00Z
ECMWF AT LATER TIMES AND USED THAT RUN (AS OPPOSED TO THE 12Z GFS)
NEXT WEEK AS THE LAST SYSTEM DROPPED SOUTHEASTWARD OVER THE
EASTERN ALEUTIANS. THE PATTERN SUPPORTS NEAR AVERAGE TEMPERATURES
WITH PRECIPITATION FOCUSED MOSTLY IN THE PANHANDLE. INLAND AREAS
IN THE SE INTERIOR WILL ALSO BE FAVORED FOR SOME RAINFALL AS
MID-LEVEL ENERGY ROTATES AWAY FROM THE UPPER LOW AND TO THE NW
ALONG THE SW SIDE OF THE UPPER RIDGE IN NW CANADA.


FRACASSO


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