Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
633 PM EST Wed Jan 29 2020
Valid 12Z Sun Feb 02 2020 - 12Z Thu Feb 06 2020
Upper pattern will largely maintain troughing in the Bering Sea
into western Alaska with ridging east of about 150W. Within that
orientation, several features will propagate through the North
Pacific and Gulf and try to bring in milder temperatures to at
least southwestern areas of the mainland. Precipitation focus will
lie primarily along/east of the Kenai peninsula and especially
into the Panhandle given the continued onshore flow. Second area
will be over southwestern/western Alaska as low pressure weakens
on Monday.
The 12Z guidance came into very good agreement for the rather
complicated pattern, but with the ECMWF leading the way in
run-to-run continuity, opted to use a deterministic blend for the
Sun-Tue period. Ensemble means may be lagging behind the
deterministic runs in the evolution of the lead system, in
particular the old parent low that is forecast to wrap back to the
east and northeast as northern stream energy rotates around the
backside of the main weakening upper low. This scenario was
contingent upon a couple things coming together but the several
runs of the guidance in that fashion suggest it has some merit.
For next Wed/Thu, the 12Z GFS/Canadian/ECMWF were nearly in line
taking that low into the AKPEN and then Gulf with its frontal
system approaching the Panhandle. To the west, better agreement
exists between the models and ensembles with another system of
modest strength near the western Aleutians.
Temperatures will moderate from well below average to within
several degrees of average over portions of at least southwestern
Alaska, but how quickly that happens is uncertain. The dense cold
air may be reluctant to budge at the surface despite increased
southerly flow aloft. Again trended a bit slower to raise
temperatures than the NBM or most guidance.
Precipitation will be favored along the coast from the Aleutians
eastward. Several inches of liquid equivalent (~3-5") are possible
for the Panhandle, especially from Yakutat southward along the
coastline.
Fracasso
Additional 3-7 Day Hazard information can be found on the WPC
medium range hazards chart at:
https://www.wpc.ncep.noaa.gov/threats/threats.php
Hazards:
- Heavy precipitation across portions of mainland Alaska and the
Aleutians, Sun, Feb 2.
- Heavy precipitation across portions of the Alaska Panhandle and
mainland Alaska, Mon-Tue, Feb 3-Feb 4.
- High winds across portions of mainland Alaska and the Aleutians,
Sat-Sun, Feb 1-Feb 2.
- Much below normal temperatures across portions of mainland
Alaska, Sat-Mon, Feb 1-Feb 3.
- High significant wave heights for coastal portions of mainland
Alaska and the Aleutians, Sun-Mon, Feb 2-Feb 3.
WPC medium range Alaskan products including 500mb, surface
fronts/pressures progs and sensible weather grids can also be
found at:
https://www.wpc.ncep.noaa.gov/alaska/ak_5dayfcst500_wbg.gif
https://www.wpc.ncep.noaa.gov/alaska/akmedr.shtml
https://www.wpc.ncep.noaa.gov/alaska/ak_5km_gridsbody.html