Gale Warning 246, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
439 AM AKST Tue Mar 8 2022

.ANALYSIS AND UPPER LEVELS...

Upper level longwave pattern continues, with ridging encompassing
much of the State and the Gulf of Alaska, and troughing over the
Bering and Aleutian Chain. Most of the precipitation that can be
seen on radar is over the Kuskokwim Delta with some light returns
over Cook Inlet. While most of Southcentral continues to see
mostly clear skies, cloud cover has started to roll back in over
Kodiak Island and the Kenai Peninsula. Ridging weakens through
Wednesday as an incoming shortwave moves northwards across the
Gulf. Thus, anticipate cloudy skies and active weather to return
to Southcentral.

&&

.MODEL DISCUSSION...

Models remain in relatively good overall synoptic agreement
through the short term. Solutions continue to struggle with the
development of multiple new surface lows forming within the
longwave trough along the Aleutian Chain. Most of the
inconsistency resides in center location and speed of each system.
Model spread continues to grow by Thursday morning with both the
cluster of lows near the Eastern Aleutians and the system west of
Attu Island, showing a variety of possibilities across each
solution.

&&

.AVIATION...
PANC...VFR conditions and light winds will persist, however,
cloud ceilings may drop below 5000' late Wednesday night.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 and 2)...

Clouds are moving into Southcentral Alaska from the southwest this
morning as a weakening upper level wave moves up Cook Inlet and to
the Alaska Range today. This wave could produce a snow flurry but
does not look to have much punch beyond that. The main event is
with the next front that is over Kodiak early this morning and
bringing them the rain and easterly winds. This front will push
into Southcentral overnight and into Wednesday bringing moisture
and warmer temperatures to the Cook Inlet region as well as north
Gulf coast on Wednesday. This will once again make determining the
precipitation type the biggest forecast challenge. Model agreement
on temperature is not very good with the GFS being a bit colder
than most other models and therefore it is favoring snow.
Temperatures aloft are rising a bit (even on the GFS model) with
surface temperatures over much of the area being in the mid to
upper 30s Wednesday. This was the case last Saturday as well but
the amount of above-freezing temperatures from the 2000 to 5000
ft layer is much different than Saturday where is was below
freezing in that whole layer and only needed some evaporative
cooling to bring the temperatures of the lower column of air
enough for snow. This is closer to many of the systems in the
second half of February that brought rain. One big thing to note
for Anchorage bowl and the Matanuska Valley is that it does not
appear that there will be southeast winds at the surface at any
time during this event. That does bring in a chance of brief
freezing rain late tonight into Wednesday morning before the
expected snow turns to rain. Either way it does look to mix with
rain from the Kenai Peninsula northward to the Matanuska Valley.

Once we get to Thursday, there is some colder air aloft moving
into the area from the southwest. The cooling airmass will likely
be enough to shift precipitation type back to snow by Thursday for
most of Southcentral Alaska. Of course, by that time there will
just be some lingering shower around and not area wide
precipitation.

&&

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

A low pressure system centered north of the Kuskokwim Delta is
continuing to push a front northward across Southwest Alaska.
Ahead of the front has been reporting snowfall, whereas, behind
the front has been reporting rain as warmer air is being drawn
northwards with the front and its parent low. This generalized
trend in precipitation type is expected to continue as far north
as the southern Kuskokwim Delta, where after steadier snowfall
through early this morning, will see a chance of rain showers/ a
rain snow mix today.

A longwave trough will begin to dominate the Bering today as a
longwave ridge over the Northeast Pacific tracks eastward. Various
shortwaves rotating around the aforementioned trough will track
north toward Southwest Alaska, which will result in multiple
rounds of precipitation through the end of the week. Models are
having problems handling how these shortwaves will progress, so
uncertainties arise with precipitation timing, intensity, and
location. The first shortwave to impact the area will spread
precipitation northward from the North Pacific this afternoon.
Precipitation is expected to start off as snow. However, the
airmass moving into the area is warmer than the previous system.
Therefore, snow will transition to a rain/snow mix and then
eventually to all rain being the predominant precipitation type
for Bristol Bay by Wednesday. As the shortwave progresses
northward, rain may begin to mix with snow in the southern
portions of the Kuskokwim Delta and Lower Kuskokwim Valley. This
will especially be evident during the daytime on Wednesday and on
the western (downslope) side of the mountains. Further north in
the Kuskokwim Valley, a long duration light snow event is
expected. Model spread increases even more past Wednesday, but a
general consensus can be met that the warmer air being drawn up
from the North Pacific begins to get cut off as a weak low tracks
north into the eastern Bering and occludes. This will lead to
temperatures cooling and a gradual return to a rain/snow mix for
inland portions of Bristol Bay Wednesday night into Thursday.
Blowing snow for the Kuskokwim Delta may occur as temperatures
cool Thursday. However, forecast confidence is low due to model
uncertainty.

&&

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

A front associated with a broad North Pacific low will stall near
the western Aleutians through Wednesday and pivot into the
central Aleutians. This will bring gusty easterly winds and rain
to the area. Winds will gradually weaken as the front and its
parent low lift northward and exit the Bering. A broad, weak low
pushes a front through the eastern Aleutians on Wednesday and will
result in a round of rain. The low will then cross the southern
portion of the of the Alaska Peninsula and into the eastern Bering
through Thursday. Its front will move over the Pribilof Islands
as northeasterly winds develop, leading to the potential for
blowing snow. Models are having problems agreeing on the exact
track of the aforementioned low and its front. Therefore, forecast
confidence beyond Wednesday begins to decrease.

&&
.Marine (Days 3 through 5: Thursday through Saturday)...

Gulf of Alaska: Wind and waves will decrease/subside as a gale
force barrier jet along the north Gulf coast starts to weaken by
Thursday morning. A series of lows will track from the western
Gulf into the eastern Bering Sea from Friday through Saturday.
Confidence is moderate to high that winds will be less than 35 kts
and seas less than 20 ft.

Bering Sea: A swath of high end small craft northeast winds with
gale force gusts will likely persist over the northern Bering Sea
through Friday night. Northeasterly winds will also increase along
the ice edge west of St. Matthew by Thursday. For the rest of the
Bering Sea and Aleutian Islands, confidence is moderate that
winds will be less than 35 kts and seas less than 20 ft through at
least Saturday evening. By Saturday night, a North Pacific low
will approach the southern Bering Sea. There is a potential for
gales and elevated seas as the low moves further north toward the
Eastern Aleutians and Alaska Peninsula. However, there is model
uncertainty with the overall track, position, and strength
associated with this low. Therefore, forecast confidence in this
feature is low.

&&

.Long Term Discussion (Days 4 through 7: Friday through
Monday)...

A Rex block regime is likely to be present out in the west at the
onset of the extended range on Friday, with a nearly closed off
upper ridge drifting near the international date line over
Siberia while a complex upper level low meanders over the Bering
and Western Aleutians. This pattern should help keep the
prevailing storm track south of the outlook area out along the
main Pacific jet axis through early next week, while very weak
flow aloft over most of Alaska will result in very slow progress
for a couple weak systems over the Gulf and across the Bering
through the end of this week. Models are unsurprisingly
struggling with the weak steering aloft and diverge significantly
for the details of these weaker lows In spite of the poor
agreement for smaller scale features, the consensus is for these
systems be low impact and remain mainly over marine areas. The one
exception will be along the North Gulf Coast, where a stalled
front will focus areas of rain and snow until an offshore pressure
gradient develops on Saturday as a low moves south of the Gulf
and surface high pressure builds over Southcentral.

A pattern change is becoming more likely at the start of next week
between Sunday and Monday, with models beginning to latch on to
the potential for a polar low to dive south out of the Arctic and
approach the Southwest by Monday evening. This could usher in much
colder temperatures over Southwest and perhaps Southcentral by
early next week. However, this possible cold shot will almost
surely be subject to change, with uncertainty still high for
quickly the upper level low moves south around the Siberian
blocking ridge.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...Gale Warning 131 138 177 178
   Heavy Freezing Spray Warning 185
FIRE WEATHER...NONE.

&&

SYNOPSIS AND MODEL DISCUSSION...KM
SOUTHCENTRAL ALASKA...EZ
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...NS
MARINE/LONG TERM...MF/AS