Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
203 PM EST Sat Jan 19 2019

Valid 12Z Wed Jan 23 2019 - 12Z Sun Jan 27 2019

Longwave pattern still exhibits above average predictability with
increased upper ridging over western Canada and eastern Alaska
with troughing through the Bering Sea across the western/central
Aleutians. However, the embedded systems of smaller scale show
little predictability and continuity in successive runs from any
deterministic model, so confidence in system timing/strength is
low. In addition, the ensembles continue to shift with each run
and have trended toward a farther west trough/ridge axis than
yesterday.

Used the ensemble means (GEFS/ECMWF ens mean) as a starting point
given their better (though blurred) consistency. The shift in the
upper low in the Bering may now tug a system that tracks
underneath it to pull into the Bering next weekend, though those
details may still change. Enough agreement existed between the 12Z
GFS and 00Z ECMWF early in the period to use them in conjunction
with the means through next week. 12Z GFS was closer to the means
as the next low lifts across the Aleutians so used that as the
deterministic weight next weekend.

What at least remains the same is 1) moderating trend in
temperatures with sustained southerly flow aloft that should work
its way to the surface eventually and 2) increased/persistent
rain/snow from Kodiak/Southcentral into the Panhandle as fronts
lose eastward progression. Should the next significant system lift
into the Bering next weekend, precipitation focus would turn back
to the Aleutians (from 160W eastward).


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