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FXAK02 KWNH 241855
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ALASKA EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
254 PM EDT TUE MAY 24 2016

VALID 12Z SAT MAY 28 2016 - 12Z WED JUN 01 2016

THUS FAR GUIDANCE HAS BEEN SHOWING ABOVE AVERAGE SPREAD AND RUN TO
RUN VARIABILITY WITH RESPECT TO THE EVOLUTION OF NERN PAC INTO ERN
BERING/MAINLAND ALASKA RIDGING.  SOLNS HAVE RANGED BTWN AN OPEN
RIDGE AND A CLOSED HIGH AND WITH VARIED LOCATIONS AND
ORIENTATIONS... SOME SUFFICIENTLY FAR WWD/SWWD TO ALLOW A DECENT
AMOUNT OF ENERGY TO CROSS THE NERN HALF OF THE MAINLAND.  BASED ON
DATA THROUGH THE 06Z CYCLE THE 00Z ECMWF ENSEMBLE MEAN HAS
GENERALLY BEEN THE MOST STABLE PIECE OF GUIDANCE OVER RECENT RUNS
THOUGH THE 00Z VERSION SHOWS SOME MEANINGFUL DETAIL ADJUSTMENTS TO
THE S OF 60N LATITUDE AROUND DAYS 4-5 SUN-MON.  IN ADDITION
TELECONNECTIONS RELATIVE TO THE MOST PROMINENT HGT ANOMALY CENTERS
FAVOR MAINTAINING A DECENT MEAN RIDGE INTO THE MAINLAND... ARGUING
AGAINST SOLNS THAT BRING LOWER HGTS INTO THE MAINLAND.  THUS
PREFERRED TO WEIGHT TODAY`S FCST MORE IN THE DIRECTION OF THE 00Z
ECMWF MEAN... WITH MINORITY WEIGHTING OF THE 06Z GEFS MEAN TO
ACCOUNT PARTIALLY FOR SOME GUIDANCE BEING STRONGER AND MORE CLOSED
WITH THE RIDGE.  THE NEW 12Z MODEL RUNS SUGGEST INCREASED
PROBABILITY OF A STRONGER/CLOSED HIGH THOUGH NOT TO THE EXTENT OF
THE 00Z CMC WHOSE STRENGTH HAD PARTIAL SUPPORT FROM ONLY A HANDFUL
OF 00Z CMC/GEFS/ECMWF ENSEMBLE MEMBERS COMBINED.  THE 06Z GFS/00Z
ECMWF WERE CLOSE ENOUGH TO THE MEANS ON DAY 4 SAT TO GIVE MORE
WEIGHT TO THOSE OPERATIONAL SOLNS AT THE START OF THE PERIOD.
AFTER SAT THERE WAS DECENT MODEL/ENSEMBLE SUPPORT FOR PULLING THE
WEAK NRN PAC SYSTEM FARTHER S OF THE ALEUTIANS THAN FCST BY THE
GFS RUNS.  12Z SOLNS STILL HAVE VARIED IDEAS ON THIS SYSTEM WHICH
HAS HAD HIGH SENSITIVITY OVER RECENT DAYS.

UPSTREAM THERE IS GENERALLY BETTER CLUSTERING AND CONTINUITY FOR A
SYSTEM COMING INTO THE PICTURE OVER THE WRN ALEUTIANS/SWRN BERING
SEA... THOUGH LATTER PERIOD DETAILS WILL HINGE ON THE EVOLUTION OF
RIDGING TO THE EAST.  THE ENSEMBLE MEANS MAY BE A BIT ON THE WEAK
SIDE BUT OFFER A REASONABLE APPROACH FOR DEALING WITH THE SPREAD
THAT DEVELOPS BY NEXT TUE-WED.  AT THAT TIME THE INITIAL ENSEMBLE
MEAN BLEND WAS STRENGTHENED SLIGHTLY FOR SFC PRESSURES AND ASSOC
WINDS.

RAUSCH

$$





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