Prognostic Meteorological Discussion
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FXAK02 KWNH 221822
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ALASKA EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
222 PM EDT FRI MAY 22 2015

VALID 12Z TUE MAY 26 2015 - 12Z SAT MAY 30 2015

OVER THE MAJORITY OF THE MAINLAND AND PANHANDLE... IN PRINCIPLE
MOST OPERATIONAL MODELS APPEAR TO HAVE TRENDED SOMEWHAT TOWARD THE
MORE STABLE AND AGREEABLE ENSEMBLE MEANS REGARDING THE RIDGE ALOFT
THAT SHOULD REBUILD AFTER DEPARTURE OF WEAK ENERGY THAT SHOULD BE
NEAR THE SRN COAST/PANHANDLE EARLY IN THE PERIOD.  HOWEVER
GUIDANCE IS STILL UNDECIDED OVER HOW ENERGY WITHIN THE INITIAL
SHRTWV MAY SPLIT AND THE SHAPE/PATH OF WHAT ENERGY PASSES OVER THE
PANHANDLE.  AMONG VARIOUS OPERATIONAL MODEL POSSIBILITIES THE 12Z
GFS SEEMS ONE OF THE LESS LIKELY OPTIONS WITH AN UPR LOW THAT
SETTLES NEAR THE SRN PANHANDLE AND THEN RETURNS NWD.  CONSENSUS
MODEL/ENSEMBLE BLEND YIELDS A MORE SHEARED FEATURE THAT SEEMS
REASONABLE GIVEN PROXIMITY OF THE MEAN RIDGE.

THE FCST REMAINS DIFFICULT FOR EVOLUTION FROM THE BERING SEA
THROUGH THE NRN PACIFIC WITH SOME INFLUENCE EXTENDING INTO THE WRN
MAINLAND.  ALREADY AT THE START OF THE PERIOD 12Z TUE THERE ARE
MEANINGFUL SFC LOW TRACK DIFFS WITH THE LEADING SYSTEM OVER THE
BERING SEA... ASSOC WITH ABOVE AVG SENSITIVITY IN UPR FLOW DETAILS
OVER THE BERING SEA/SIBERIA.  AS OF 12Z TUE SFC LOWS FROM
INDIVIDUAL 00Z GEFS/ECMWF ENS MEMBERS RANGE FROM THE BERING SEA
JUST E OF 170E SEWD TO JUST S OF THE ALEUTIANS NEAR 170W.
CONTINUITY SEEMS TO FAVOR A SOLN CLOSER TO THOUGH NOT IDENTICAL TO
THE 00Z ECMWF/ECMWF MEAN OVER THE SRN BERING SEA.  BY WED-THU THE
PAST COUPLE DAYS OF OPERATIONAL GFS/ECMWF/CMC RUNS HAVE BEEN
SUGGESTING THAT A WRN TO NRN PAC WAVE MAY TRACK AT LEAST AS FAR
NWD AS THE ALEUTIANS AND PSBLY INTO THE BERING SEA WITH SOME
DEGREE OF INTERACTION WITH THE INITIAL BERING SEA SYSTEM.
CURRENTLY THE 00Z ECMWF MEAN IS ONE OF THE SLOWER/WEAKER SOLNS
WITH THE WRN-NRN PAC WAVE.  CONFIDENCE IS STILL BELOW AVG BUT
GIVEN ONGOING SIGNALS FROM THE MULTIPLE OPERATIONAL MDLS... PREFER
TO BEGIN INCLUDING AT LEAST A HINT OF THE OPERATIONAL SCENARIO.
INTERESTINGLY THE LATEST ENSEMBLE MEANS CONVERGE REMARKABLY WELL
AT THE SFC BY DAY 7 FRI.

COMBINING THE ABOVE CONSIDERATIONS... THE STARTING BLEND INCLUDES
00Z ECMWF/ECMWF MEAN AND 00Z NAEFS MEAN/12Z GFS DAYS 4-5 TUE-WED.
THIS BLEND USES GREATER WEIGHTING OF THE ECMWF-BASED GUIDANCE AND
BALANCES ENSMEAN/OPERATIONAL IDEAS OVER THE BERING SEA/NRN PAC
WHILE DOWNPLAYING UNCERTAIN DETAILS ALOFT NEAR THE PANHANDLE.
SOME WEIGHTING OF THE 00Z ECMWF CAN BE MAINTAINED ALONG WITH THE
ENSMEANS THROUGH DAY 6 THU WHILE PREFS ADJUST TO THE NAEFS/ECMWF
MEANS EXCLUSIVELY BY DAYS 7-8 FRI-SAT.

RAUSCH

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