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492
FXAK02 KWNH 291828
PMDAK

ALASKA EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
228 PM EDT FRI AUG 29 2014

VALID 12Z TUE SEP 02 2014 - 12Z SAT SEP 06 2014

THE ALASKAN FLOW PATTERN REMAINS HIGHLIGHTED BY A SIGNIFICANT
ARCTIC VORTEX NEAR THE NORTH SLOPE NEXT WEEK ALLOWING FOR A
PROLONGED PERIOD OF UPPER-LEVEL TROUGHING FROM THE ARCTIC OCEAN
THROUGH THE INTERIOR. EXPECT BELOW NORMAL TEMPS FOR MUCH OF ALASKA
AS 500/700 MB HEIGHT ANOMALIES WILL CENTER 2-3 STANDARD DEVIATIONS
BELOW NORMAL NORTH OF THE ARCTIC CIRCLE. THE PATTERN SHOULD ALLOW
MODEST LINGERING IMPULSES AND SURFACE DEVELOPMENT UNDERNEATH OVER
THE ALASKAN SRN/SERN TIER BOTH OVER/FROM THE GULF OF AK AND LATE
WEEK UPSTREAM SOUTH OF THE ALEUTIANS. THE 00 UTC ECMWF IN
PARTICUALAR SHOWS MORE STREAM INTERACTION/PHASING THAN COMPARED TO
OTHER DETERMINISTIC MODELS UP INTO THE BERING SEA/SW ALASKA NEXT
WEEK...BUT THIS DOES NOT SEEM SUPPORTED AT THIS POINT ENOUGH BY
ENSEMBLES OR WATER VAPOR LOOPS TO EMBRACE. A QUICK PEEK AT THE
NEWER 12 UTC ECMWF STILL SHOWS PHASING BUT WITH LESS VIGOR.

GIVEN DETERMINISTIC UNCERTAINTY...THE WPC ALASKAN MEDIUM RANGE
PRODUCT SUITE HAS BEEN DERIVED FROM AN ENSEMBLE MEAN FORECAST
APPROACH. THE 00 UTC GFS ENSEMBLE MEAN WAS PRIMARILY USED AS BEST
MAINTAINS PATTERN CONTINUITY WITH EMBEDDED FEATURES WHILE
REMAINING REASONABLY COMPATABLE...ESPECIALLY ALOFT...WITH 00 UTC
ECMWF/NAEFS ENSEMBLE MEANS.

SCHICHTEL

$$






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