Prognostic Meteorological Discussion
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FXAK02 KWNH 231933
PMDAK

Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
230 PM EST Fri Feb 23 2018

Valid 12Z Tue Feb 27 2018 - 12Z Sat Mar 03 2018

...Guidance/Predictability Assessment and Weather
Highlights/Threats...

Model and ensemble offer reasonably compatable larger scale
patterns into medium range time scales. This pattern is
highlighted aloft at high latitudes by a cold Arctic closed
trough/low. Strong height falls/shortwave energy digging down
across the interior then southern/southeastern Alaska early to
mid-next week will provide a cold shot across the region with
unsettled wintery conditions. Underneath, unusually large timing
differences that were evident recently with the flow of energetic
lows and frontal systems working from the north Pacific
northeastward to Alaska have decreased with latest gudiance. A
lead system and associated weather/high seas swath moving rapidly
across the southern/southeastern tier of the state and Gulf of
Alaska early in the forecast period. This constitues a significant
WPC continuity change from yesterdays much less progressive progs
valid early next week. The adjustment seems warranted now
condsidering the strong guidance trend signal and upstream water
vapor imagery that shows quite a potent supporting jet from
eastern Asia to the western Pacific.

The pattern reloads upstream mid-later next week with development
of a deep Bering Sea low, high seas, and downstream
rebuilding/amplified Gulf of Alaska to western/southwestern Alaska
mid-upper level ridge. System approach would eventually threaten
western/southwestern Alaska with organized late next week weather.

Accordingly, the WPC medium range product suite was primarily
derived from a blend of the GFS/ECMWF days 4-6 and then mostly
ensemble means into days 7/8.

Schichtel



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