Prognostic Meteorological Discussion
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FXAK02 KWNH 121805
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ALASKA EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
205 PM EDT SAT JUL 12 2014

VALID 12Z WED JUL 16 2014 - 12Z SUN JUL 20 2014

GUIDANCE CONTINUES TO STRUGGLE WITH DETAILS FOR THE OVERALL MEAN
TROUGH EXPECTED TO DEVELOP JUST W/NW OF THE MAINLAND AS WELL AS
FOR THE SYSTEM OVER THE NRN PACIFIC AS OF DAY 4 WED.  THIS
ULTIMATELY LEADS TO FURTHER INCREASES IN UNCERTAINTY BY THE LATTER
HALF OF THE PERIOD AS THE TWO FEATURES INTERACT.  IN SPITE OF THE
SPREAD AND DAY TO DAY VARIABILITY WITH SOME ASPECTS OF THE FCST...
BY THE END OF THE PERIOD MULTI-DAY MEANS FROM MODEL/ENSMEAN SOLNS
SHOW REMARKABLY GOOD AGREEMENT WITH THE EXPECTED LARGE SCALE
PATTERN CONSISTING OF THE TROUGH JUST NW OF THE MAINLAND AND A
RIDGE CENTERED BETWEEN ALASKA AND HAWAII.

SHRTWVS WITHIN THE NRN STREAM MEAN TROUGH WILL INFLUENCE
WAVINESS/POSN OF A SFC FRONT EXPECTED TO AFFECT THE NRN MAINLAND.
CURRENTLY GUIDANCE IS SPLIT AS TO WHETHER LEADING SHRTWV ENERGY
EJECTS ACROSS THE NRN MAINLAND WHILE UPSTREAM ENERGY FEEDS INTO
THE MEAN TROUGH VERSUS INITIAL ENERGY REMAINING IN PLACE AS IT
COMBINES WITH UPSTREAM FLOW.  THE 00Z GFS/CMC REPRESENT THE
EJECTING SCENARIO WHILE THE 06Z GFS/00Z ECMWF GENERALLY MAINTAIN
ONE TROUGH AS DO THE ENSEMBLE MEANS.  THE 12Z GFS BRINGS LEADING
ENERGY FARTHER EWD INTO THE WRN MAINLAND BUT STILL DOES NOT EJECT
IT.  YDAYS MODEL/ENSMEAN CONSENSUS FOLLOWED THE IDEA OF
MAINTAINING A SINGLE TROUGH SO WOULD PREFER TO MAINTAIN CONTINUITY
AS MUCH AS POSSIBLE UNTIL THERE IS BETTER SUPPORT FOR AN
ALTERNATIVE EVOLUTION.

WITH THE NRN PAC/ALEUTIANS SYSTEM THE 06Z GFS IS A PRONOUNCED
EXTREME ON THE NRN SIDE OF THE ENVELOPE WITH ITS BEST DEFINED SFC
LOW BY EARLY DAY 5 THU.  IT IS AN OUTLIER VERSUS 00Z
GEFS/ECMWF/CMC ENSEMBLE MEMBERS THOUGH BARELY WITHIN THE SPREAD OF
06Z GEFS MEMBERS.  THE 12Z GFS STRAYS TO THE FAST/ERN SIDE OF THE
SPREAD FROM THE START OF THE FCST EARLY WED.  COMPARING OTHER
GUIDANCE... OPERATIONAL MODELS GENERALLY AGREE THAT THE UPR LOW
SHOULD REMAIN BETTER DEFINED AND A LITTLE SLOWER THAN THE ENSEMBLE
MEANS BY NEXT THU-FRI.  INTERESTINGLY AS OF EARLY FRI THE 00Z
GFS/ECMWF/CMC DIFFER SIGNIFICANTLY ON SFC LOW STRENGTH/DEFINITION
EVEN THOUGH THEIR UPR LOWS ARE ABOUT THE SAME DEPTH.  ALSO IT IS
AROUND THIS TIME THAT EVOLUTION OF THE NRN STREAM TROUGH IS LIKELY
TO BEGIN HAVING AN INFLUENCE ON TIMING/TRACK.  BASED ON THE
DISTRIBUTION OF GUIDANCE SOME WEIGHTING OF THE OPERATIONAL
CLUSTER... BEST REPRESENTED BY THE 00Z ECMWF... IS REASONABLE
THOUGH ENSMEAN PREFS FOR THE NRN STREAM TROUGH REQUIRE INCLUSION
OF THEIR SOLNS AS WELL ESPECIALLY IN THE LATTER HALF OF THE
PERIOD.

COMBINED PREFS FOR BOTH PRIMARY FEATURES RESULT IN A STARTING
POINT BLEND OF HALF 00Z ECMWF AND THE REMAINDER 00Z ECMWF MEAN/00Z
NAEFS MEAN/06Z GEFS MEAN FOR DAYS 4-7 WED-SAT... FOLLOWED BY 80
PCT WEIGHTING OF THE ENSEMBLE MEANS BY DAY 8 SUN TO EMPHASIZE THE
MORE AGREEABLE LARGE SCALE PATTERN.

RAUSCH

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