Gale Warning 18, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
551 AM AKST Sun Jan 5 2025

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

Discussion:

Today is the start to more complicated forecast period...with strong
winds, a variety of precipitation types across Southcentral, periods
of moderate to heavy rain for Gulf coastal areas, and heavy snow
anticipated for higher elevations, including Thompson Pass.

Over the past 24 hrs, warmer air has pushed northwards across the
Gulf. Cordova has seen the greatest swing in temperatures as
yesterday mornings temperatures in the mid teens has warmed into the
mid 40s as of this morning. They should remain warm enough to remain
all rain through the next few systems working into the region.
Warmer air has begun to push into Prince William Sound as well as
the eastern Kenai Peninsula. Whittier and Seward have seen a steady
increase in temperatures and should nudge past freezing a bit later
this morning and snow will change over to rain. Cold air still
entrenched near Valdez, and it will take additional time to moderate
temperatures there. Ongoing snow and gusty winds continue this
morning for Thompson Pass which will make for difficult travel.
Elsewhere, temperatures remain cold enough that any precipitation
should remain mostly snow this morning.

This first rather compact Gulf system will move into the Prince
William Sound this morning before moving inland. Coastal areas along
the Gulf might see a brief respite before the next trough and
associated front approach later this morning/early afternoon. This
will bring an additional push of warmer air on modest southerly
flow, and widespread precipitation to the coastal regions. Lower
elevations on the Gulf side should see any lingering snow changeover
to rain (with the exception of Valdez). Several more rounds to
moderate to heavy rain are possible through at least midweek for
these areas, as each system brings a good fetch of moisture with it.
The parent low of the aforementioned trough will move over the
eastern Aleutians/southern AKPEN by tomorrow morning. However,
another system will deepen as it rapidly lifts north along the
eastern periphery towards Kodiak Island. Models have been trending
the surface low moving into the southern Cook Inlet then up towards
the Susitna Valley Monday night into Tuesday.

While the coast and coastal mountains will be dealing with moderate
to heavy precipitation, developing easterly cross barrier flow will
help to downslope the eastern Kenai, Anchorage, and Palmer areas
keeping there areas on the drier side. Strong southerly flow in the
mid to upper levels over the Central Chugach Mountains will allow
some moisture to make it up and over the mountains allowing for snow
and some freezing rain to make in into the southern Copper Basin.
Higher snowfall amounts look to fall south of Tonsina and west of
Tolsona to about Glacier View. However, a shift in track of each
system will impact snowfall amounts for locations in the Copper
Basin. Thompson Pass will see long duration heavy snow with the
potential for several feet of snow through Tuesday.

The other forecast concern will be for a barrier jet of storm force
winds to develop across the northern Gulf and nudge into Prince
William Sound Monday afternoon and evening. These strong winds will
funnel into the western Sound resulting in strong winds for Whittier
of up to 60 mph. Strong winds will also spill over into Portage and
the Turnagain Arm with wind gusts up to 75 mph possible. This will
make for tricky driving along the Seward Highway, especially for
higher profile vehicles. There is the potential for strong winds to
work into the Anchorage Hillside, but lesser confidence on this due
to down inlet flow as winds start to exit the Arm. Winds will
slacken as the surface low move north and general flow becomes more
southerly.

- PP

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA/BERING SEA/ALEUTIANS (Days
1 through 3: Sunday through Wednesday morning)...

An expansive trough containing multiple low centers continues to
reside over Southwest Alaska. Centered roughly 250 miles south of
Unalaska, this feature draws cold air offshore and southwest
across the Bering Sea to the Western Aleutian Islands, while
funneling relatively warm, moisture-laden North Pacific storms
across the AKPen and Southcentral into Southwest Alaska. Due to
this southerly inflow, expect 10 degree warmer temperatures this
week across the Southwest mainland.

The next of these lows crosses the AKPen late Sunday afternoon,
then lingering in the Eastern Bering between False Pass and the
Pribilofs. Its front brings light precipitation to the Kuskokwim
delta Sunday afternoon followed by a shortwave that crosses Kodiak
a few hours later, and arriving at King Salmon and Dillingham by
Monday morning. Warmer temperatures behind the front will hasten a
transition from snow to rain south of Dillingham to Lake Iliamna,
although this change may revert several times over the next
several days as a stronger low approaches Cook Inlet Tuesday
morning. This new system moves over Southwest on Tuesday then
toward the interior Tuesday afternoon pulling all the
aforementioned features behind it.

While confidence concerning the development and track of these
lows is moderated by continued model differences, confidence is
high that periodic, light to moderate precipitation will persist
across the region through Wednesday. Snow is expected dominate
north of the Pribilofs to Dillingham, rain for the eastern
Aleutians, and mixed precipitation for the AKPen. Additionally,
offshore winds from the Kuskokwim Delta will contribute to
widespread gales in the northern Bering and widespread freezing
spray with heavy freezing spray within 20 miles of the ice edge,
west and south from Mekoryuk through Wednesday.

&&

.LONG TERM FORECAST (Days 4 through 7: Wednesday through
Saturday)...

The start of the forecast period features a strong upper level
low dominating much of the Bering Sea-western mainland Alaska and
a steep ridge of high pressure along the Canadian Coast and
Eastern Alaska. The high pressure ridge will weaken and retreat
eastward slightly along the Gulf of Alaska and Southern Alaska
allowing a very strong North Pacific low and its associated fronts
to travel northward into the Gulf and into the Alaskan Peninsula
Thursday and into Friday before being absorbed by the long wave
trough of low pressure over the Baring Sea. This pattern will
bring unseasonable warmer temperatures and mixed precipitation
along the coastlines near the surface and has the real potential
for heavy snow accumulations in the higher elevations.

The upper level low will gradually retreat back into Eastern
Siberia and the Chukchi Sea as the Ridge of high pressure
reasserts its dominance Friday and into Saturday. This will
flatten out the southern portion of the long wave trough allowing
several compact surface lows and their associated fronts to
transit along the Aleutians and coastal southern Alaska.

Confidence in the model guidance is moderate with a slight bias
between the GFS and European solutions through Thursday. The
European and Canadian better handle the synoptic features Friday
and into Saturday.

DD

&&

.AVIATION...

PANC...Mainly VFR conditions will persist through the TAF period.
There could be a brief time of MVFR if some snow showers were to
make it over the mountains and to the terminal today. However, due
to strengthening southeasterly flow, most, if not all the TAF
period should be dry due to downslope drying. Northerly winds will
persist into early Monday morning before a potential brief period
of southeasterly Turnagain Arm winds ensues later in the morning.
Northerly winds become dominant again at the end of the TAF period
as flow returns to down-inlet. Low-level windshear looks to
develop this afternoon and beyond with the strengthening southeast
winds aloft while surface flow remains mostly out of the north;
except for the brief period of Turnagain Arm winds Monday
morning.

&&

SPECIAL WEATHER STATEMENT
National Weather Service ANCHORAGE AK
1253 PM AKST Sun Jan 5 2025

AKZ103-126-061500-
East Turnagain Arm-Western Prince William Sound-
Including the cities of Girdwood, Portage, Whittier, Seward,
and Moose Pass
1253 PM AKST Sun Jan 5 2025

...AREAS OF VERY LIGHT FREEZING RAIN EARLY THIS WEEK...

A series of storms will bring considerably warmer weather and a
chance of precipitation from today through Tuesday. While
temperatures are expected to gradually rise above freezing through
Monday, surface temperatures may remain below freezing due to the
recent cold weather. Rain, heavy at times, may flow across and/or
puddle on various surfaces. Untreated and snow-covered surfaces
and roadways may become extremely slick. Please exercise caution
if traveling over the next few days.