Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
532 PM EST Sat Dec 26 2020
Valid 12Z Wed Dec 30 2020 - 12Z Sun Jan 03 2021
...Deep system in the western Bering later next week...
...Overview and Guidance/Uncertainty Assessment...
Noisy/complicated/uncertain pattern to start the period will
translate into better-defined flow as a deep system enters the
Bering Sea around next Friday. With lingering uncertainty in
system placement/timing over the open Pacific, favored a
multi-center blend though with limited 12Z GFS influence over the
water. Parallel 12Z GFS clustered closer to the
ECMWF/Canadian/UKMET south of 50N giving credence to
a system farther south of the AKPen 00Z Thu than the op 12Z GFS.
Closer to Southcentral, 12Z ECMWF was much drier than the others
to start the forecast (seemingly too dry). Models and ensembles
have trended decidedly deeper with the Bering system for next
Fri-Sat, which fits the pattern of the deep western Pacific upper
low moving eastward. Trended deeper with the low, into the 950s
mb, but not as low as the operational models as low as the 930s
mb. Despite the strong center, trend continues to be progressive
again today. Triple point low will move into the Gulf around next
Saturday and steadily into the Panhandle thereafter. Subsequent
shortwave around the mean Bering circulation could tap another
surface cold front to follow in its wake. Trended toward the
ensemble means for the Fri-Sun period due to timing
spread/uncertainty.
...Weather/Hazards Highlights...
Generally lighter and scattered rain/snow is forecast for Tue-Wed
along the Aleutians and across Southcentral, with some enhancement
via stronger embedded features. Bering system will bring at least
a period of more modest rain/snowfall and certainly windy
conditions (40kts+) around the center. Triple point could provide
more focus for locally heavier rain/snow across at least parts of
the AKPen/Southcentral by next weekend. Ensembles show the
heaviest amounts over southeastern Kenai. Temperatures will
generally be near to above normal through the period, especially
over western areas of the mainland. Colder temperatures may filter
in by next weekend north of the Alaska Range.
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