Prognostic Meteorological Discussion
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FXAK02 KWNH 201838
PMDAK

ALASKA EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
238 PM EDT MON APR 20 2015

VALID 12Z FRI APR 24 2015 - 12Z TUE APR 28 2015

THE PRIMARY FOCUS OF THE FCST WILL BE TOWARD THE ONGOING SERIES OF
PROGRESSIVE NRN PAC/BERING SEA SYSTEMS FEEDING INTO NERN PAC MEAN
TROUGH/UPR LOW THAT SHOULD BECOME SOMEWHAT DEEPER BY THIS
WEEKEND... PLUS PSBL NERN PAC SYSTEM INTERACTION.  GUIDANCE HAS
BEEN WAFFLING ON THE SMALLER SCALE DETAILS OVER THE MAINLAND AND
VICINITY BUT ON AVG HINT AT SOME DEGREE OF WEAK RIDGING.  SUCH A
MODEST MEAN RIDGE TELECONNECTS WELL WITH THE NERN PAC TROUGH/UPR
LOW AND POSITIVE HGT ANOMALIES EXPECTED OVER NRN CANADA.
FORTUNATELY DETAIL DIFFS ALOFT OVER THE MAINLAND DO NOT APPEAR TO
HAVE A SIGNIFICANT IMPACT ON THE SFC PATTERN WHICH SHOULD REFLECT
BROADLY CYCLONIC FLOW FROM THE WEEKEND ONWARD.

TO INCORPORATE THE MOST COMMON IDEAS OF LATEST GUIDANCE AND
MAINTAIN SOME LEVEL OF DETAIL... INITIAL FCST BLENDS START WITH A
PRIMARY EMPHASIS ON THE 00Z ECMWF/ECMWF MEAN WITH MODEST INCLUSION
OF THE 00Z NAEFS MEAN.

DURING THE PAST FEW DAYS GUIDANCE HAS BEEN SHOWING DAY TO DAY
OSCILLATIONS WITH TIMING OF THE SYSTEM TRACKING FROM THE BERING
SEA/ALEUTIANS INTO THE NERN PAC EARLY IN THE PERIOD.  AS OF 12Z
FRI THE 00Z UKMET/CMC AS WELL AS 06Z/12Z GFS RUNS THAT ARE
SOMEWHAT NWD OF THE 00Z RUN SEEM TO SUPPORT LEANING TOWARD THE
ECMWF SCENARIO AT THE START OF THE FCST.  AFTER FRI THERE IS A
FAIR AMOUNT OF SPREAD REGARDING PSBL EVOLUTION OF A SYSTEM TO THE
E ASSOC WITH LEADING SHRTWV ENERGY THAT COULD CONCENTRATE/CLOSE
OFF.  AT THE MOMENT WOULD LIKE TO WAIT FOR FURTHER SUPPORT BEFORE
GOING TO THE GFS/UKMET IDEA OF QUICK AND PRONOUNCED CLOSING OF
THIS LEADING ENERGY.  THE RESULTING AREA OF MEAN LOW PRESSURE HAS
ADJUSTED SLIGHTLY NWD FROM 24 HRS AGO.

FOR THE SYSTEM REACHING THE BERING SEA BY SUN... LATEST SOLNS
DISPLAY SOMEWHAT GREATER SPREAD THAN YDAY WITH MORE VARIATION IN
TIMING AND EXTENT TO WHICH THE SYSTEM MAY GET SHEARED AS FLOW
ALOFT BRIEFLY BECOMES MUCH FLATTER OVER THE WRN 2/3 OF THE
PACIFIC.  THE PREFERRED BLEND HELPS TO MAINTAIN SOME ELEMENTS OF
CONTINUITY.

RAUSCH

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