Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
549 PM EST Sun Dec 27 2020
Valid 12Z Thu Dec 31 2020 - 12Z Mon Jan 04 2021
...Deep system in the western Bering late this week with strong
winds...
...Overview and Guidance/Uncertainty Assessment...
Upper pattern for Alaska will be driven by the eastward
progression of a deep upper low from the northwestern Pacific into
the Bering Sea and then into the Gulf of Alaska. Weak ridging over
the Interior later this week will slip northwestward into
northeastern Russia and beyond, allowing lower heights from the
Yukon to move into the Tanana Valley and Y-K Delta next weekend
into next Monday. The 12Z guidance was clustered enough so that a
mostly deterministic blend sufficed to start. The GFS was again
just a bit removed from the ECMWF-led cluster (though that also
contained the parallel GFS), especially with an offshore system
well south of the Aleutians Thursday that will lift into the Gulf
by Friday. Over the Bering, models continue to advertise a very
deep low in the 930s mb or so and have trended lower accordingly
given the consistent trends the past few days. Progressive flow
will keep any frontal system moving steadily eastward, including
another Pacific system underneath the Bering low next weekend.
Trended toward much more ensemble weighting by next Sun-Mon as
timing becomes much more uncertain with these smaller-scale
features.
...Weather/Hazards Highlights...
Deep Bering system will bring at least a period of modest
rain/snowfall and certainly windy conditions (40-50kts+) around
the center. Parent low will take several days to wind down,
maintaining scattered precipitation for the Aleutians/Bering
Sat-Tue. Triple point low detaching from the occlusion could
provide more focus for rain/snow across at least parts of the
AKPen next weekend, though this has trended a bit farther south.
The Panhandle may see several rounds of rain/snow as each system
moves through. Temperatures will start near to above normal,
especially over western areas of the mainland, Thu-Fri. By the
weekend into next week, colder temperatures will filter in from
the east. Anomalies of 5-15 degrees below normal may be common
north of the Alaska Range with some pockets of near to slightly
above normal temperatures near the Brooks Range. Below zero highs
will be likely with lows 10-30 below in the valleys.
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
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