Gale Warning 785, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
456 PM AKST Mon Dec 4 2023

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 through 3:
Tonight through Thursday)...

A gale force low tracking slowly north over the Gulf of Alaska
this evening will lead to primarily marine/coastal impacts
tonight, with increasing precipitation spreading inland through
the week. With the slow moving low only inching northward, its
front remains out over the northern Gulf, allowing cold air to
remain entrenched near the surface over the Copper River Basin.
As a result, northerly gap winds for the Valdez/Thompson Pass area
will remain persistent around the same intensity through at least
Wednesday if not into Thursday. Low-level temperatures over
western portions of Southcentral will be warmer tonight, keeping
winds lighter through Resurrection Bay and Passage Canal.

For Tuesday, a neutrally-tilted trough pushes in across Western
Alaska. Compared to yesterday, models now tilt this trough
slightly negatively with time and are in much better agreement on
this solution. However, models continue to disagree on the
placement of the surface low. The forecast philosophy with a
negatively tilted trough approaching Southcentral Alaska would
favor moisture being drawn northwest from the Gulf low, similar to
the scenario depicted in the GFS solution. As a result, the
forecast today has trended in that direction. This places a band
of precipitation over the western half of the Copper River Basin,
extending westward across the Chugach Front Range and the
Talkeetna Mountains into Anchorage and the Mat-Su Valleys. These
areas may see up to 6 inches of snow through Wednesday afternoon,
with several more inches possible through Wednesday night and into
Thursday, depending on how quickly the trough progresses and
pushes the band of precipitation eastward. Higher amounts will be
possible in the southern Copper River Basin & Thompson Pass, where
more moisture is wrung out over the coastal mountains. Blowing
snow is expected to be an additional hazard for Thompson Pass as
cold air continues to filter out through gaps, leading to
continued sustained winds of 40 to 50 mph.

By Wednesday, the low moves into the northeastern Gulf, drawing
cold air across the Western Alaska Range. This cold air advection
is likely to enhance gap winds in the western Gulf to storm
force, with gusts in excess of 65 knots (75 mph). For Wednesday
evening, this should begin to push precipitation eastward and
eventually clear it out of Southcentral. Though, as mentioned
above, the timing of this progression is uncertain at this time.
For Thursday, a broad low with a strong upper-level component
tracks into Western Alaska. Its cold front brings potential for
another round of snow to Southcentral as it sweeps eastward out
over the Gulf.

CQ

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA AND BERING SEA/ALEUTIANS
(Days 1 through 3)...

The forecast remains on track for Southwest and the Bering Sea
with mostly zonal flow and weak ridging over the Bering and a
broad trough and low pressure system over the Gulf. This pattern
combines the cold air moving south from the Bering Strait with the
forcing of the low in the Gulf to produce strong and gusty winds
along the Alaska Peninsula (AKPen), particularly through areas
like King Cove, Sand Point and Chignik. These winds will slowly
let up and shift east through Wednesday afternoon as the Gulf low
weakens. Between the more zonal/weak ridging over the Bering and
the broad low in the Gulf exists an area of deformation, which has
brought light today from the foothills of the Alaska Range south
to Pilot Point. This will let up quickly this evening as things
shift to the east.

Over the Bering expect cooler temperatures, westerly winds and
show showers to persist through the forecast period. This is
mainly due to ample cold air streaming east and southeast across
the Bering. This will be reinforced by a low developing over
Kamchatka tonight that will stream east into the Norton Sound by
Thursday. This will amplify the westerly winds, reinforce the cold
air, and lead to heavier snow/snow showers for the Bering and
western coastlines of the Mainland and AKPen. Snow will also push
farther into the interior Wednesday and Thursday as this low
drives into Norton Sound and eventually the interior.

-Jones

&&

.LONG TERM FORECAST (Days 4 through 7)...Friday through Monday...

The longwave trough over the eastern Bering and western Alaska,
meanders and drifts southeastward into the Gulf of Alaska with a
surface low heading toward the eastern Gulf of Alaska. There is
low confidence for the weekend period with the location of the
surface and where the heaviest precipitation will be, but
expecting an active pattern ahead for eastern Alaska. High
pressure ridging continues indicate amplification for the western
Bering Sea that encourages cool, northerly flow across the Bering
Sea. Snow showers can be expected under the northerly flow,
especially for the central and east Bering. A closed low forms
over Southern Mainland, and drifts to the East through the
weekend.

A North Pacific low with more available moisture and winds
approaching gale force will lift northward toward the Aleutians,
but looks to drift east toward the Gulf before reaching the
Islands. Bands of precipitation would still be reinforced and
would like keep precipitation going, locally heavier at time along
the Aleutians. Another surface low appears to develop and south
of the Alaska Peninsula and tracks into the western Gulf. At this
time, potentially heavy precipitation (10 percent exceedance of 2
inches in 24 hours) to the northern Gulf coast early next week is
possible. There is still low confidence with the position of the
low this far out in time, but is a feature worth tracking over the
next few days.

rux

&&

.AVIATION...

PANC...VFR conditions will persist through this evening as
northerly winds around 10 to 15 mph slowly diminish. The remnants
of a front moving northeast across the Chugach/Kenai Mountains
could produce a period of light snow late tonight or early Tuesday
morning. However, dry air continuing to filter in from the north
coupled with the short window for favorable lift will limit
snowfall duration and intensity, and ceiling/visibility is
unlikely to drop towards MVFR range for more than a couple hours
or so early on Tuesday morning.

AS

&&