Wind Chill Advisory 4, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
533 AM AKST Wed Dec 21 2022

.ANALYSIS AND UPPER LEVELS...

Cold and clear conditions continue to blanket much of the
southern Mainland as high pressure lingers overhead and cold
Arctic air filters into the valleys. For Southcentral, the
coldest temperatures persist across portions of the Copper River
Basin and Mat-Su Valleys (-20s to -40s). Patchy fog and low
stratus developed overnight across the Anchorage area south to the
northwestern Kenai Peninsula. Light snowfall has started for the
western Chugach and eastern Kenai Mountains this morning as a
result of a weakening low pressure system near Prince William
Sound.

For Southwest Alaska, not only are conditions clear and cold, but
they are very windy, too, especially along the coast. The already
frigid temperatures coupled with gusty northeasterly offshore
winds is creating very cold wind chills for the Kuskokwim Delta,
as low as 45 below zero. Thus, a Wind Chill Advisory remains in
effect until late this morning for the Kuskokwim Delta.

Out west, a stationary front drapes across much of the domain,
specifically from the eastern Aleutians northwest to the western
Bering. Strong and widespread easterly winds accompany the front,
where gusts to storm-force are expected. Rain is occurring for the
eastern Aleutians, while the Pribilof Islands are getting snow
with the cooler temperatures.

&&

.MODEL DISCUSSION...

Models are coming into better agreement with the synoptic pattern
expected for the next few days. There is consensus for a front to
lift into the southern Gulf by this evening and then remain
nearly stationary over the entire Gulf until the end of the work
week. The associated low center is generally advertised to reach
the southern Gulf by Friday morning, however model agreement
begins to diverge beyond this time in regards to the exact track
and placement of the low. Out west, there is good agreement that
the large stationary front will begin to break down late Thursday
into Friday as a North Pacific surface low elongates and tracks
into the southern Bering.

&&

.AVIATION...

PANC...Patchy fog and low stratus may continue to move in and out
of the Anchorage terminal area through the morning. VFR
conditions and light northerly winds will otherwise persist
outside of any periods of low stratus that manage to move back
over the terminal.

&&

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

A ridge to the north and another ridge across the Gulf with a
trough of low pressure that is shearing apart will bring mostly
clear skies and below normal temperatures through Friday. Patchy
areas of fog and stratus are expected through the morning around
Anchorage and along and near the Knik Arm as well as parts of the
eastern Kenai Peninsula to near Soldotna. Lingering mid level
clouds across the Copper River Basin have kept temperatures a bit
warmer than past couple of night, but these clouds are expected to
clear out later this morning. A shortwave will move southward
today a may slightly increase the northerly winds especially near
Valdez, Thompson Pass and the Copper River Delta where the best
energy will be albeit fairly weak.

Our attention then turns to a frontal system moving into the
southern Gulf and Kodiak Island later today. This will bring a
quick shot of snow before changing to rain in most populated
areas including Kodiak City where an inch or two of snowfall is
expected. Light snow will also push into the eastern Kenai
Peninsula where a couple inches of snow are possible in populated
areas. Winds will also increase significantly with gales quickly
ramping up to high end gales and pockets of storm force winds
across the southern Gulf, Shelikof Strait, and the Barren Islands.
Even pockets of hurricane force wind gusts are possible in these
areas but are expected to be short lived. This front will stall
across the southern Gulf and slowly weaken late Thursday into
Friday with the winds slowly decreasing.

Finally, another stronger shortwave will move towards
Southcentral Thursday night and Friday which will bring colder air
towards the Copper River Basin along with a tightening pressure
gradient between a surface high across northern Alaska and a low
pressure system across the southern Gulf. These forces will
combine and may produce strong winds across the Matanuska Valley
with winds gusts up to 60 mph beginning Thursday night and
continuing into Friday. Winds may also increase across Thompson
Pass and Valdez where gust of 55 to 65 mph are possible. There is
a chance that these winds could reach high wind criteria of 75
mph, however confidence is low right now. Stay tuned as we refine
the forecast.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 through 3: Today
through Saturday)...

An upper-level low located north of Bethel continues to track
northwestward across the region today. Simultaneously a ridge of
high pressure will be pushed back over Southwest as a North
Pacific low tracks towards the eastern Aleutians. This will
result in warmer temperatures across the region and a mix of rain
and snow showers over the Alaska Peninsula this afternoon into
Thursday morning. A chance of light snow showers is possible for
the Bristol Bay and Kuskokwim Delta coasts as the low moves
northward into the eastern Bering Sea Thursday afternoon and
evening. Cooler temperatures will work their way back into the
region for Friday, but will mostly stay in the single digit
positives for day-time highs and then drop to single digit
negatives for night-time lows as cloud cover will help moderate
temperatures. The exception will be the Kuskokwim Valley where
night-time lows could drop to the double digit negatives. Drier
weather and offshore flow will continue across the region through
Saturday, except along portions of the Alaska Peninsula as
easterly to southeasterly flow could cause additional rain showers
for upslope locations.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 through 3: Today
through Saturday)...

An active weather pattern will persist through the forecast
period. A stationary front associated with a low in the western
Bering, is currently extending from the eastern Aleutians
northwest through the central Bering. This front is aiding in
tightening the pressure gradient between the low pressure in the
western Bering and the high pressure located over Mainland Alaska,
resulting in gusty conditions throughout the central Bering to
the northwest Bering. Widespread gales are located in the Bering
along with a southeast to northwest oriented belt of storm force
winds that exists over the central Bering. Storm force winds also
develop on the Bering and Pacific sides of the Alaska Peninsula
tonight into Thursday morning as a North Pacific low and its
associated front both lift northward and track into the region.
Rain should be the main precipitation type with this system with
the possibility of a rain/snow mix as well in some locations. One
thing to note is that the Pribilof Islands could have enough
dynamic cooling from higher precipitation intensity to produce a
period of snow for tonight into early Thursday and then switch
back over to a rain/snow mix. Winds will start to relax heading
into the weekend with the continued chance of precipitation across
the region as multiple systems traverse through the Bering.

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

Overall synoptic pattern appears to be in agreement, but the
details of the forecast could have quite a different result. In
the upper levels, an upper trough elongates as it dips southwest
across the state. This low appears to cut off and continue
westward where a broad area of troughing exists this weekend
through Tuesday. This offshore motion would help with advecting
cooler air out of the interior, especially this weekend.
Temperatures below normal could linger into next week with this
flow regime. Meanwhile, the weather becomes more active in the
Gulf with southeasterly flow and multiple easterly waves passing
along the coast. The coldest temperatures over Southcentral will
be this weekend, followed by a rebound to more seasonable
temperatures for the week.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...WIND CHILL ADVISORY: 155.
		 FLOOD WARNING: 185.
MARINE...STORM WARNING: 130-132, 138, 150, 155, 160, 165, 179-181,
						185, 351, 352, 411, 412, 414
		 GALE WARNING: 119, 120, 136, 137, 139, 140, 170-172, 413.
		 HEAVY FREEZING SPRAY: 130, 139, 140, 160, 180, 181, 185.
FIRE WEATHER...NONE.

&&

SYNOPSIS AND MODEL DISCUSSION...AF
SOUTHCENTRAL ALASKA...RC
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...NS
LONG TERM...VR