Prognostic Meteorological Discussion
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FXAK02 KWNH 241815
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ALASKA EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
214 PM EDT FRI APR 24 2015

VALID 12Z TUE APR 28 2015 - 12Z SAT MAY 02 2015

THE WPC ALASKAN MEDIUM RANGE PRODUCT SUITE HAS BEEN PRIMARILY
DERIVED FROM A BLEND OF THE COMPATABLE 12 UTC GFS AND 00 UTC ECMWF
INTO DAY 4 TUESDAY TO DEPICT ENHANCED SMALLER SCALE DETAIL WHEN
DETERMINISTIC MODEL VARIANCE IS STILL MODEST.

SWITCHED TO A BLEND OF THE STILL REASONABLY COMPATABLE
GEFS/NAEFS/ECMWF ENSEMBLE MEANS DAYS 5-8 TUE-NEXT SATURDAY. THIS
WAS CONDUCTED AS PER ANCHORAGE/FAIRBANKS WFO COORDINATION AND
CONSIDERING RAPIDLY GROWING DETERMINISTIC MODEL FORECAST SPREAD.
OF THE ENSEMBLES...LEANED HARDER ON THE ECMWF MEAN THAT OFFERS
SLIGHTLY BETTER CONTINUITY. ADDITIONAL WPC FORECASTER APPLIED
ADJUSTMENTS OFFER SLIGHTLY DEEPER OCEANIC LOWS CONSISTENT WITH
FAVORABLE UPPER LEVEL SUPPORT. OVERALL...THIS SOLUTION OFFERS GOOD
WPC CONTINUITY IN A PERIOD WITH DECREASING PREDICTABILITY.

AS HAS BEEN THE CASE RECENTLY...A FORECAST FOCUS REMAINS THE
ONGOING SERIES OF NRN PAC/BERING SEA SYSTEMS FEEDING INTO NERN
PAC/GULK OF AK MEAN TROUGH/UPPER LOW. THIS PATTERN FAVORS A
PROLONGED PERIOD WITH POTENTIAL FOR MODEST PCPN INTO SRN/SERN
ALASKA AS FUELED BY CENTRAL GULF OF ALASKA MEAN LOW WRAPPED
MOISTURE. DETAIL DIFFERENCES ALOFT OVER THE INTERIOR WITH A FEW
WEAK SYSTEMS STILL DO NOT APPEAR TO HAVE A SIGNIFICANT IMPACT ON
THE SURFACE PATTERN WHICH SHOULD REFLECT BROAD CYCLONIC FLOW FOR
MUCH OF NEXT WEEK IN A GENERALLY BENIGN MILD/WARM PATTERN.

THE NEXT UPSTREAM SYSTEM IS STILL EXPECTED TO WORK ACROSS THE
S-CENTRAL BERING SEA MONDAY BEFORE FEEDING SEWD INTO THE LEAD GULF
OF AK MAIN MEAN TROUGH TUESDAY ON THE BACKSIDE OF A MAIN GULF OF
ALASKA LOW/SYSTEM. LATEST SOLUTIONS CONTINUE TO DISPLAY GREATER
SPREAD WITH MORE VARIATION IN TIMING AND EXTENT TO WHICH UPSTREAM
SYSTEMS INTERACT/SHEAR AS FLOW ALOFT BECOMES FLATTER AND MORE
COMPLEX. THE WPC BLEND MAINTAINS SOME ELEMENTS OF CONTINUITY AND
ALLOWS FOR SOME PERIODS OF MODEST ALEUTIAN TO SWRN AK PCPN
POTENTIAL. GUIDANCE SHOWS A CONTINUED SERIES OF SYSTEMS TRACKING
ACROSS THIS REGION TUE-NEXT SATURDAY...ALBEIT WITH GREATER
UNCERTAINTY FOR DETAILS BUT WITH DECENT/SLOWLY AMPLIFYING OVERALL
PATTERN SUPPORT.

SCHICHTEL

$$




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