Prognostic Meteorological Discussion
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000
FXAK02 KWNH 211850
PMDAK

Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
249 PM EDT Mon May 21 2018

Valid 12Z Fri May 25 2018 - 12Z Tue May 29 2018

Forecast over the high latitudes has become rather unpredictable
as a result of a lack of steady anomaly centers as well as shifts
in the flow over NW Canada. The thinking for several days was for
the upper high over British Columbia would slowly ease westward
toward the northern Panhandle by next week, but the ensembles have
trended away from that idea in favor of keeping it east of 120W.
That allows the upper low in the Gulf to be more progressive which
seemed to open the upstream Pacific up to a couple other systems
from both the northern and southern stream but the models have yet
to settle on timing/track. Even the ensemble systems were out of
line, making a blend difficult. To the north, an upper high will
likely spill over from north of Wrangel Island to the Beafort Sea
but strength and E-W location differs greatly among the
models/ensembles. Tried to form a middle ground solution via the
00Z NAEFS and ECMWF ensemble mean, with some detail from the 12Z
GFS and 00Z ECMWF/Canadian early in the forecast (Fri-Sat) before
their forecasts diverged. Still kept a reinforced upper high in
the Arctic into next week per the ensemble consensus with lower
heights from the interior and western Alaska into the Gulf.

The upstream Pacific flow was quite chaotic and out of phase, so
finding common ground was difficult. However, ongoing continuity
worked fairly well as it was at least in the middle of the very
broad clustering (~1000km). This kept one system well south of the
Aleutians as it wrapped into the in situ upper low in the Gulf
Sun/Mon with another possible system moving into the western
Aleutians/Bering next Mon/Tue. Confidence was rather low around
the edges of Alaska with the most agreement over the interior,
caught in between the highs/lows.


Fracasso


WPC medium range Alaskan products including 500mb, surface
fronts/pressures progs and sensible weather grids can be found at:

http://www.wpc.ncep.noaa.gov/alaska/ak_5dayfcst500_wbg.gif
www.wpc.ncep.noaa.gov/alaska/akmedr.shtml
http://www.wpc.ncep.noaa.gov/alaska/ak_5km_gridsbody.html


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