Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
226 PM EST Mon Feb 05 2018

Valid 12Z Fri Feb 09 2018 - 12Z Tue Feb 13 2018

Models and ensembles generally support the erosion/suppression of
the upper ridge across the interior by next week, but how that
unfolds remains ensconced in uncertainty. Relative measure of
predictability decreases with time, indicating an even steeper
loss of predictability relative to lead time; i.e., ensembles were
of utmost use in the forecast by this weekend. Only the 00Z ECMWF
ensemble mean was used for the Mon/Tue forecast next weekend as it
fit the progression of the system lifting northward out of the
Pacific (slower than the forecast yesterday).

Upstream upper pattern will feature a deep upper low swinging
through northeastern China this weekend which will help amplify a
rather short wavelength ridge into the western Aleutians and then
a sharp trough along 170W. The flow will be complicated by the
southward movement of the upper ridge to between 40-50N south of
the Gulf of Alaska. Used a blend of the recent GFS/ECMWF and their
ensemble means to form a consensus with the lead systems into the
Gulf Fri-Sat. For Sun-Tue, considering continuity and the track of
recent deterministic runs, opted to rely on the better defined and
slower ECMWF ensemble mean over the GEFS mean which was much too
washed out. This would take that system northward then
northeastward into the Gulf as the upper ridge sinks southward.
Finally, another system would approach the western Aleutians early
next week.

Used an ensemble blend for the temperatures/PoPs and other surface
weather grids in light of ensemble spread. Precipitation should be
modest along the coastal areas from the eastern Aleutians over to
the Panhandle -- several inches over several days though some days
would have heavier periods of rain with approaching fronts and/or
near the sfc lows (i.e., Kodiak and southeastern Kenai peninsula).


Fracasso