Prognostic Meteorological Discussion
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FXAK02 KWNH 101809
PMDAK

ALASKA EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
209 PM EDT THU JUL 10 2014

VALID 12Z MON JUL 14 2014 - 12Z FRI JUL 18 2014

LATEST MODEL/ENSEMBLE GUIDANCE APPEARS TO SHOW AVERAGE OR BETTER
AGREEMENT WITH THE LARGE SCALE FCST BUT MEANINGFUL SENSITIVITY FOR
SOME DETAILS IS EVIDENT OVER THE NRN PACIFIC/ALEUTIANS/SRN BERING
SEA AND EVENTUALLY INTO THE NERN PAC.

ACROSS HIGHER LATITUDES MOST SOLNS EXPECT ONE SHRTWV TO EJECT
ACROSS THE NRN MAINLAND EARLY IN THE PERIOD FOLLOWED BY A MEAN
TROUGH DEVELOPING OVER THE VICINITY OF 180 LONGITUDE.  THE 00Z
ECMWF AND TO A SLIGHTLY LESSER EXTENT ECMWF MEAN ARE DEEPEST WITH
THE INITIAL SHRTWV... THOUGH AT LEAST THE 00Z ECMWF IS MORE
PROGRESSIVE THAN ITS PAST COUPLE RUNS AND THE 12Z GFS HAS TRENDED
PARTIALLY TOWARD THE ECMWF SCENARIO.  TOWARD THE END OF THE PERIOD
THE 00Z ECMWF AGAIN LOWERS HGTS ALOFT MORE THAN CONSENSUS OVER THE
NRN-CNTRL MAINLAND.

FARTHER SWD THE PRIMARY QUESTION IS TO WHAT EXTENT UPSTREAM NRN
PAC ENERGY WILL INTERACT WITH THE CLOSED LOW INITIALLY JUST S OF
THE ALASKA PENINSULA.  00Z-06Z GFS RUNS ARE ON THE FAST SIDE OF
THE SPREAD WITH THE UPSTREAM ENERGY AND THUS END UP INCORPORATING
THE ERN UPR LOW INTO THE OVERALL MID LVL SYSTEM... VERSUS EJECTING
THE LATTER NEWD... AND ARE FARTHER EWD/NEWD WITH THE NRN
PAC/ALEUTIANS SFC SYSTEM.  THE 12Z GFS SHOWS A MEANINGFUL TREND
TOWARD THE MAJORITY CLUSTER THAT IS SLOWER WITH THE WRN-NRN PAC
SYSTEM AND EVENTUALLY EJECTS THE UPR LOW ENERGY INITIALLY S OF THE
PENINSULA.  IT REMAINS A QUESTION MARK HOW STRONG THE EJECTING
SHRTWV WILL BE BY THE TIME IT REACHES THE NERN PAC/SRN MAINLAND SO
PREFER TO DECREASE 12Z GFS/00Z ECMWF WEIGHTING BY DAYS 7-8 THU-FRI.

AHEAD OF THIS NRN PAC EVOLUTION THERE IS A FAIR AMOUNT OF SPREAD
WITH A WEAK WAVE THAT MAY TRACK NWD TOWARD THE PENINSULA/KODIAK
ISLAND.  OVERALL THE LATEST GUIDANCE SUGGESTS A WEAKER WAVE THAN
YDAYS CONSENSUS FCST.

BASED ON ABOVE CONSIDERATIONS DAYS 4-6 MON-WED START WITH A
MODEL/ENSEMBLE MEAN COMPROMISE... HALF 12Z GFS/00Z ECMWF AND THE
REMAINDER 00Z NAEFS/ECMWF MEANS.  LOWER CONFIDENCE IN STRENGTH OF
ENERGY ALOFT THAT MAY EJECT ACROSS THE EXTREME NERN PAC/SRN
MAINLAND LATE IN THE PERIOD LEADS TO MINIMAL WEIGHTING OF THE
OPERATIONAL RUNS BY NEXT THU-FRI WHILE THE 00Z ECMWF MEAN
COMPRISES THE LARGEST PCT OF THE FCST BLEND.

RAUSCH

$$





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