Wind Chill Advisory 3, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
524 PM AKST Tue Dec 20 2022

.ANALYSIS AND UPPER LEVELS...
Deep cold remains over most of mainland southern Alaska today with
high pressure remaining over the surface of the state and a cold
upper level low aloft. The weak low near the north Gulf coast
remains nearly stationary from a day ago through it is pushing
some mid-level clouds into the Copper River Basin which has warmed
temperatures near Glennallen from around -45F up to -25F this
afternoon.

The big weather action is in the Bering Sea and Eastern Aleutians
where there is a stationary frontal boundary between the high
pressure over the Northern Bering Sea and a low in the Western
Aleutians. This front is quite long and has a moisture tap that
originates around 20N with the location seen on satellite as being
just east of the Hawaiian Islands. This tropical moisture feed has
dropped over three inches of rain on Unalaska Island.
Interestingly enough, Akutan which is not all that far to the east
of Unalaska received less than half an inch. Strong winds are
occurring near this front along the Aleutians through the Pribilof
Islands.

&&

.MODEL DISCUSSION...

Model agreement continues to improve in regards to the north Gulf
of Alaska low with Hi-resolution models bringing the weak low
into Prince William Sound overnight and then dissipating it
Wednesday.

The next low that will move into the Gulf late this week has a
considerable spread on its track between models. This will impact
the Kodiak forecast and the Gulf of Alaska marine forecasts more
than anywhere else. The Bering Sea will still be mainly affected
by the strong front that is across it through the week, but there
is indication this frontal boundary will weaken later in the week.
By the weekend the different models mostly want to push some low
from the Pacific toward the Bering, but the solutions are both
scattered and clunky.

&&

.AVIATION...
PANC...Fog and stratus will continue to move in and out of the
Anchorage terminal area through tomorrow morning.

&&

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

A weakening low pressure system currently situated near Middleton
Island will move into Prince William Sound (PWS) tonight. Light
snow with this system is expected to continue for the eastern
Chugach Mountains before shifting to the western Chugach and Kenai
Mountains Wednesday morning. Meanwhile, a northerly flow pattern
with mostly clear skies and well below temperatures will likely
persist for the rest of the week across the southern mainland.

A front extending ahead of a North Pacific low reaches the north
Gulf coast Wednesday afternoon. This will bring another round of
snow for the eastern Kenai Mountains, with lighter accumulations
elsewhere along the coastal mountains. For the low-lying areas,
Kodiak City will see a brief period of light snow before
transitioning to all rain by early Wednesday afternoon as the
atmospheric column of air warms above the surface. Otherwise, most
the precipitation will stay south of PWS.

Over the coastal waters, increasing easterly winds associated the
front will reach to storm force with hurricane gusts possible
sometime between Wednesday night and Thursday morning. There
remains some model disagreements with the track and position of
the low over the Gulf, but winds are expected to slowly decrease
to gales beginning on Friday. An Arctic trough pushes southward
across the mainland, bringing another surge of polar air with
continued dry and colder conditions.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 through 3: This afternoon
through Friday afternoon)...

Quiet and cold weather continues for Southwest Alaska as the ridge
to the west continues to weaken its grip on the west coast and
become more concentric off the coast of northwest Alaska in the
Chukchi Sea. An upper low is moving westward over the area is
providing colder air for tonight as low temperatures dip into the
negatives, even along the coast; and well into the negative teens
in twenties for interior locations, especially the middle
Kuskokwim Valley. Temperatures will be warmer Wednesday area wide,
but especially for the coast as a front associated with a North
Pacific low lifts northward into the Alaska Peninsula (AKPEN)
also sending warmer air northward with it. Most precipitation
associated with this front remains confined to the AKPEN Wednesday
afternoon through Thursday morning. There is some chance the
Bristol Bay coast and Kuskokwim Delta coast could see light
precipitation as the low moves northward into the eastern Bering
Sea Thursday afternoon and evening; snow amounts, if any, will
remain light. Colder conditions return for Friday as the Bering
Sea pulls away westward. The only exception will be portions of
the AKPEN easterly to southeasterly flow could cause additional
rain showers for the favored upslope locations.

&&

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

The active pattern continues for the Bering Sea, Aleutians, and
the Pribilof Islands. The pressure gradient between low pressure
in the western Bering and higher pressure over Mainland Alaska is
causing gusty/blustery conditions throughout the central Bering to
the northwest Bering. There are widespread gales in the Bering along
with a southeast to northwest oriented belt of storm force winds
that exists over the central Bering and is forecast to further
elongate and potentially impact the Pribilof Islands early
Wednesday morning. The storm-force wind belt then retreats off the
northwest through Wednesday afternoon and evening. Storm force
winds also develop on the Bering and Pacific sides of the Alaska
Peninsula Wednesday night into Thursday morning as a North Pacific
low and its front both lift northward and track into the region.
Rain should be the main precipitation type with this system.
However, the Pribilof Islands could have enough dynamic cooling
from higher precipitation intensity to produce a period of snow.
The current thinking is that this would be most likely be
overnight Wednesday into very early Thursday morning before
switching back to rain/snow mix. At this point, it is not expected
for temperatures to reach freezing or below, but they will be
close. Snow amounts would not to anything impactful and will only
be a couple inches if it accumulates. There is still uncertainty
somewhat with the temperature forecast for the Pribilofs, so pay
attention to additional forecast updates as they become available.
Elsewhere, the western Aleutians also have the chance at some
rain/snow mix at times during the short-term period as multiple
systems traverse through the western Bering and North Pacific.

.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...FLOOD WARNING 185.
MARINE...STORM 132 138 150 155 165 179 180 185 352 411 412 414.
GALE 120 130 131 136 137 139 160 170 171 172 181 351 413.
HEAVY FREEZING SPRAY 130 139 140 160 180 181 185.
FIRE WEATHER...NONE.

&&

SYNOPSIS AND MODEL DISCUSSION...EZ
SOUTHCENTRAL ALASKA...MF
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...DN
LONG TERM...VR