Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
432 PM EST Wed Jan 15 2025

Valid 12Z Sun Jan 19 2025 - 12Z Thu Jan 23 2025

...Stormy pattern from Western Alaska through the Alaskan southern
tier...


...General Overview...

Stormy weather will continue through the upcoming holiday weekend
into next week for parts of the Aleutians,
Northwest/Western/Southwest Alaska, and the Southern Coast with
plenty of onshore flow ahead of mean troughing through the
Aleutians and Alaska Peninsula. A couple of shortwaves rotating
through the base of this trough will lift across western Alaska,
eventually working into strong ridging extending from the Gulf
into Mainland Alaska. Another deepened upper low/trough looks to
amplify across the Aleutians and into the Bering Sea next week to
renew a stormy flow track conduit into these regions again with
the rebuilding of the downstream upper ridge next week.

...Model Guidance Assessment...

Latest models and ensembles generally continue a recent trend for
relatively good agreement on the overall synoptic pattern, but
plenty of uncertainty in the details. Much of the uncertainty
surrounds smaller scale shortwaves rounding through the base of
the larger scale trough over the Bering/Aleutians and as energies
lift poleward on the western periphery of an ambient and amplified
blocky ridge downstream up over the mainland. This includes
individual surface/triple point lows lifting towards the AK
Peninsula to Southern Coast into this weekend, which will work to
enhance local winds/precipitation. The bulk of guidance agrees
that one shortwave this weekend should act to briefly push upper
ridging over the Mainland/Southeast eastward to a degree, but
should build back again ahead of the next trough into the
Bering/Aleutians early next week. This pattern may generally
repeat into mid-later next week, albeit with less amplitude.

Again prefer today a composite of reasonably clustered larger
scale 12 UTC ECMWF/UKMET/Canadian guidance to provide maximum
detail as consistent with predictability Sunday-Monday. The 12 UTC
GFS seems to crash energy too much into the ambient blocking upper
ridge versus running system energies more up the periphery. Opted
to switch to best compatible GEFS/ECMWF/Canadian ensemble means
guidance amid slowly growing forecast spread through later time
frames. This maintains good WPC product continuity.

...Weather/Hazards Highlights...

Heavy precipitation/winds will spread across South-Central and
parts of Southeast Alaska through the holiday weekend as a
broadening closed low expands slowly eastward, shifting the
atmospheric river from the Pacific slowly in that direction with
time as tempered by the blocking ridge. The stronger wind flow
should also work inland and be enhanced from terrain up
through/over the Alaska Range. Rain should linger across the
Aleutians and into southwest AK through the period. There is now a
stronger signal for moderate to heavy snow/blowing snow and high
wind chances increasing for western/Northwest Alaska as well into
this weekend, and to a lesser extent the Interior. Above normal
temperatures will make rain the main precipitation type in
southwest AK and for coastal locations, but wintry mixed
precipitation and snow is likely farther north and at elevation.
Rain falling on top of snow could enhance snowmelt and lead to
localized flooding concerns in some areas. The strong nature of
the low will also likely produce strong gusty winds from the
Aleutians to western Alaska across the Bering Sea and Bering
Strait up through the western/Northwest AK coast. A lingering
front and strong pressure gradient may make the Northern Slope
breezy as well.

Schichtel


Additional 3-7 Day Hazard Information can be found on the WPC
medium range hazards outlook 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