Prognostic Meteorological Discussion
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FXAK02 KWNH 271933
PMDAK

ALASKA EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
332 PM EDT THU JUL 27 2017

VALID 12Z MON JUL 31 2017 - 12Z FRI AUG 04 2017

ENSEMBLES REMAIN IN GOOD AGREEMENT ON THE LONGWAVE PATTERN NEXT
WEEK WHICH MAINTAINS THE UPPER LOW IN THE GULF. AREAS OF MODEL
CONTENTION LIE ALONG AND NORTH OF 70N AND ALSO THROUGH THE BERING
SEA. THE ECMWF HAS GENERALLY LED THE GUIDANCE RECENTLY IN TERMS OF
BETTER VERIFICATION (OR AT LEAST BEING FIRST TO SHOW A SCENARIO)
THOUGH IT HAS NOT BEEN PERFECT. WITH THE CONCURRENCE OF ITS
ENSEMBLE MEAN TODAY, OPTED TO USE THEIR 00Z FORECAST AS THE
MAJORITY BASIS OF THE FORECAST. THE 06Z/12Z GFS WERE CLOSE TO BUT
A BIT REMOVED FROM THE ECMWF-LED FORECAST, BUT REPRESENTED A
MOSTLY REASONABLE SOLUTION AS WELL THOUGH HAD RESERVATIONS ABOUT
HOW STRONG IT WAS IN THE ARCTIC/BEAUFORT WHILE THE ENSEMBLES
SUGGESTED KEEPING HEIGHT FALLS FARTHER NORTH/NORTHWEST. EVEN THE
00Z ECMWF WAS LIKELY TOO DEEP WITH AN INCOMING UPPER LOW OUT OF
NORTHEASTERN RUSSIA TOWARD THE STRAIT BY NEXT FRI.

TREND WAS TO SLOW DOWN THE APPROACHING SYSTEM THROUGH THE GULF
NEXT MON-WED AS LEAD ENERGY SHOULD SLIDE NORTHEASTWARD AHEAD OF IT
ON MONDAY WHICH ALLOWS THE TRAILING UPPER LOW TO BE SLOWER. AFTER
THAT, KEPT THE NEXT SYSTEM DIVING SOUTHEASTWARD ACROSS THE
EASTERN/CENTRAL ALEUTIANS AND ROUND THE BASE OF THE UPPER TROUGH.
FARTHER WEST, THE GFS HAS BEEN MORE INSISTENT ON BRINGING A SYSTEM
NORTHWARD AROUND THE UPPER/SFC HIGH SITUATED SOUTHWEST OF THE
ALEUTIANS WHILE THE OTHER MODELS AND MOST ENSEMBLES LEAVE IT IN
THE MID-LATITUDES NEAR OR WEST OF THE DATELINE. HOWEVER, LATEST
12Z ECMWF LOOKED MUCH MORE LIKE THE LATEST 12Z GFS WITH THAT
SYSTEM, BUT IT WAS SLOWER THAN THE 06Z GFS AND KEPT IT OVER THE
FARTHEST WEST ALEUTIANS ISLANDS BY NEXT THU/FRI.


FRACASSO


$$




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