Prognostic Meteorological Discussion
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FXAK02 KWNH 181852
PMDAK

ALASKA EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
251 PM EDT THU SEP 18 2014

VALID 12Z MON SEP 22 2014 - 12Z FRI SEP 26 2014

WPC ALASKAN MEDIUM RANGE SURFACE FRONTS/PRESSURES AND 500MB PROGS
ALONG WITH ASSOCIATED SENSIBLE WEATHER GRIDS HAVE BEEN PRIMARILY
DERIVED FROM A BLEND OF COMPATABLE GUIDANCE FROM THE 06 UTC GFS
ENSEMBLE MEAN AND 00 UTC ECMWF ENSEMBLE MEAN. RECENT DETERMINISTIC
MODELS SEEM TOO RUN TO RUN INCONSISTENT...BUT DESPITE AMPLE
FORECAST SPREAD...DECIDED TO INCORPORATE A SMALL PERCENTAGE OF THE
GFS/ECMWF CONSIDERING RECENT TRENDS TOWARD MORE AMPLIFIED
MID-UPPER LEVEL TROUGHING/COOLING LINGERING DOWN INTO THE INTERIOR.

RECENT DETERMINISTIC GFS AND ECMWF MODEL RUNS HAVE BEEN ROBUST AT
TIMES BUT REMAIN OVERALL QUITE RUN TO RUN INCONSISTENT WITH
TIMING/POSITION OF MID-UPPER LEVEL TROUGH ENERGY DIGGING FROM THE
ARCTIC INTO THE ALASKAN INTERIOR THIS WEEKEND INTO NEXT WEEK AND
AS WITH ANY POTENTIAL INTERACTION WITH MORE SRN STREAM BASED FLOW.
ABOVE AVERAGE FORECAST SPREAD WITH THE FEATURE MAY STILL BEST
PORTEND AN ENSEMBLE MEAN APPROACH. THE WPC BLEND THOUGH DOES SHOW
COOLING MEAN MID-UPPER LEVEL INTERIOR TROUGH DEVELOPMENT.

AMPLE MID-UPPER LEVEL TROUGHING SETTLES OVER THE GULF OF ALASKA
THIS WEEKEND...AND GUIDANCE NOW ALLOWS LINGERING MUCH LONGER WEEK
IN AMPLIFIED MID-UPPER LATITUDE FLOW. THIS SEEMS REASONABLE NOW
CONSIDERING EXPECTATION OF ENOUGH STREAM FLOW SEPARATION.
ASSOCIATED SURFACE SYSTEM ORGANIZATION SHOULD ACCORDINGLY FAVOR
HEAVIER PRECIPITATION FROM SRN TO SERN AK. THIS ENERGY AND
WEATHER/QPF FOCUSING LOW INTERACTS NEXT WEEK WITH APPROACHING
UPSTREAM NRN PACIFIC KICKER ENERGIES. IN THIS PATTERN...WELL
ORGANIZED LOW ENERGY AND WEATHER FOCUS TRANSLATION IS LESS
PROGRESSIVE IN RECENT GUIDANCE AND NOW SINKS SEWD FROM THE WRN
ALEUTIANS MORE IN ERNEST INTO EARLY-MID NEXT WEEK TO REACH THE
GULF OF ALASKA MID-LATER NEXT WEEK. THIS FEEDS ENERGY INTO A
RENEWED MEAN TROUGH POSITION THAT LEADS TO A THREAT FOR GULF OF
ALASKA FRONTOGENESIS/CYCLOGENESIS...BUT WPC SYSTEM DEPICTION IS
NOW NOT AS WELL DEFINED CONDISERING ENERGY INTERACTION UNCERTAINTY
AND INCONSISTENCY. THE POTENTIAL REMAINS HOWEVER.

SCHICHTEL

$$





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