Gale Warning 741, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
529 AM AKST Mon Nov 21 2022

.ANALYSIS AND UPPER LEVELS...

There is a broad longwave trough from the Central Bering to the
Gulf Of Alaska with numerous shortwaves aloft. At the surface
there is a weak low over the northern Gulf and another surface low
with a magnitude of 983 mb near Sand Point. On satellite imagery
(GOES Airmass RGB), there is an elongated occlusion from the
Alaska Peninsula (AKPEN) into the northern Gulf. South of the
chain there is a jet core with an estimated magnitude of 170
knots. Also on satellite imagery (CIMSS MIMIC PW) the strongest
portion of the fetch of moisture is south of Cordova. There is a
dome of high pressure south of Attu and Shemya this morning.

&&

.MODEL DISCUSSION...

Models are in decent agreement with the major synoptic features
especially through 00z Wednesday. The main forecast challenge will
continue to be the precipitation type (p-type). The thermodynamic
profiles are different on the NAM, GFS and numerous different
high-resolution models. There are some minor differences with the
shortwaves aloft on the global and the regional models. The
forecast is going to remain tricky for portions of Southcentral.
Forecast confidence is much higher for Southwest Alaska, the
Bering Sea, and Aleutians.

&&

.AVIATION...
PANC...The cigs are going to bounce around today. Expect VFR
conditions and light winds at times. There remains a chance for
rain and/or freezing rain, especially mid-morning, in conjunction
with a weak frontal wave moving through the area.

&&

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

It is a very sloppy weather situation for Southcentral Alaska this
morning as the weak low in the Gulf moves inland over the Kenai
Peninsula. This is bringing more rain to the eastern Kenai
Peninsula and the Prince William Sound region. The rain is heading
northwestward with the low and the big question for the immediate
timeframe is whether the rain will make it to the lee side of the
mountains for Anchorage and the western Kenai Peninsula.
Temperatures in the western Kenai are still generally above
freezing, but some lower lying areas may get some brief freezing
rain this morning before it warms up. The lower elevation of
Anchorage have all dropped below freezing overnight and there
remains a concern for freezing rain this morning. The freezing
level on the 12Z Anchorage sounding is around 3000 ft so any
precipitation under the 2500 to 3000 ft level should be liquid.
The real challenge is whether the rain makes it into the Anchorage
Bowl or downslopes out in the marginal cross- barrier flow that
will remain all day. It will really be watching the radar and
seeing how the precipitation behaves as it moves over thew
Anchorage area. The most likely scenario is that a little more
rain/freezing rain occurs this morning and then ends and
temperatures warm above freezing by afternoon. It is not certain
that this rain will make it over the Chugach Mountains and is
expected to be light if it does. If the rain does pick up in
intensity, it should also be accompanied with temperatures rising
above freezing more quickly and therefore transitioning to
straight rain from freezing rain. Either way, the show should be
over by early afternoon.

The next item of increasing interest is the way there appears to
be increasing chances for rain/snow and then snow over the
Western Kenai Peninsula tonight into Tuesday. This is a very
subtle feature where there is weak cold advection and enhanced
lift occurring over the western Kenai so the chances for a little
snow tonight into tomorrow seems to be increasing. There is a
chance this area of enhanced lift sets up farther north near
Anchorage, but it is looking more like the Western Kenai at this
point.

On Wednesday, the cold upper level low which is currently over the
Northern Bering Sea will track over Kodiak Island and help to
bring a change and cooler temperature to Southcentral by
Wednesday night.

&&

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

A filling, weak low with a few embedded smaller centers will begin
to move slowly from the Alaska Peninsula (AKPEN) towards the
western Gulf by this evening. In the meantime, areas of light
rain/snow mix or drizzle will be possible across the Bristol Bay
region as stagnant air and low level moisture remain trapped in
place under a low level temperature inversion as the persistent
warm nose above it remains in place to start out. However, a
marked pattern shift will arrive from the northwest in the form of
a cold front arriving from the northwest later today and tonight.
This front will mark the leading edge of a returning push of
Arctic air descending southing from the northern Bering between
this afternoon and Tuesday, resulting in temperatures returning
below freezing across all of Bristol Bay by early Tuesday, while
also falling into the upper 10s to low 20s across the Y-K Delta
and Lower Kuskokwim Valley. Periods of snow will develop along and
behind the front as strong northwest flow becomes established
behind the front from tonight into much of Tuesday. The best
potential for snowfall will be focused along and just west of the
Aleutian and Alaska Ranges, as well as near the Kuskokwim
Mountains, where upslope enhancement will be favored. In
addition, snow showers forming out over water will likely affect
much of the Kuskokwim Delta Coast at times on Tuesday as they move
ashore. This intermittent snow will combine with northwesterly
winds around increasing to 20 to 30 mph along the coastline on
Tuesday, possibly resulting in areas of blowing snow and reduced
visibility as bands of snow move across, particularly between
Kipnuk and Toksook Bay and around Nunivak Island.

Looking towards Wednesday, expect things to dry out but remain
rather chilly as a shortwave ridge axis moves into place from the
eastern Bering and as an upper low moving southeast along the
coast moves into the western Gulf. Temperatures area-wide will dip
mostly down into the 10s both early Wednesday morning and late
Wednesday night as winds begin to relax and partial clearing
allows the surface to effectively radiate out and cool.

&&

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

A low spinning near the southern Alaska Peninsula (AKPEN) should
exit into the Gulf later this evening as a cold front and
associated push of Arctic air continues to advance from northwest
to southeast across the Bering/Aleutians. Strong northwesterly
winds to Gale force will shift from the central Aleutians to
eastern Aleutians and southern AKPEN as strong northerly flow and
cold air advection shift east with time through Tuesday.
Widespread rain and snow showers will transition to all snow by
this evening for all but the western Aleutians, then back to a
rain-snow mix for areas around Dutch Harbor by Tuesday afternoon
as a fast-moving low diving southeast quickly crosses the central
portions of the Chain and then exits into the North Pacific by
Wednesday morning. The next system of interest will follow soon
behind early on Wednesday as a gale force front extends into the
western Bering behind a transient shortwave ridge pushing across the
central and eastern Bering. A warmer air mass will push north
ahead of the front, with mainly rain arriving along the frontal
zone as it moves across the central/western Aleutians and into the
Pribilofs through Wednesday evening.

&&

.LONG TERM FORECAST (Days 4 through 7: Thursday through Sunday)

A longwave trough setting up over the state on Thursday will push
eastward through the weekend, promoting a pattern shift to colder
weather through the long term forecast period. On Thursday, a
colder airmass over Southwest Alaska will be drawn across the
Aleutian Range into the western Gulf of Alaska. In combination
with a strong low in the eastern Gulf of Alaska, this promotes
gusty winds to gale force out of bays and passes in the western
Gulf. The development of offshore flow in response to low pressure
in the Gulf also shuts off precipitation along the north Gulf
coastal mountains Thursday morning. Inland locations will stay
mostly dry, with the most likely location for potential snow in
the Copper River Basin as moisture wraps around the north side of
the eastern Gulf low and precipitation returns to the north Gulf
coast on Thursday afternoon.

Out west, there is increased confidence compared to yesterday
with the track of a large low in the northern Bering Sea. All
global models are now in agreement that the low will push a broad
swath of colder air across the eastern Aleutians and southern
Alaska Peninsula into the North Pacific, producing gusty gale
force gap winds there on Thursday as well. Additionally, the cold
air aloft will support widespread showers developing over the
relatively warm waters of the central/eastern Bering Sea and
moving into the Aleutian Chain and Pribilof Islands. The low will
also push a front along the Southwest coast. With a cold air mass
in place, this would bring mostly snow to the region. However, the
front is not expected to move very far inland, so precipitation
would be limited to coastal areas.

As an upper-level low sets up over the Gulf of Alaska,
northwesterly flow on the back side of the low will reinforce the
cold air mass over the southern mainland and shift the focus of
gap winds eastward, south of the Alaska Peninsula and into the
western Gulf for Friday. The cold, dry air mass will also keep
much of the region dry through the long term forecast period. The
Copper River Basin will continue to be the exception as cold air
filtering in across the Alaska Range into Southcentral will
continue to support periods of snowfall through Sunday. Another
low will then begin to track into the far western Bering and
pushes a potentially storm-force front northward, bringing warmer
conditions and rain to the western/central Bering Sea and
Aleutians Friday through Saturday. While much of the Bering Sea
will see warmer conditions next weekend, colder air will continue
to flow in over southern mainland Alaska, with 850 mb temperatures
dropping to -20C for some locations by Sunday, suggesting below
average temperatures for the weekend.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...Winter Weather Advisory 101.
MARINE...Gale 150-176 178-185.
		 Heavy Freezing Spray 181 185.
FIRE WEATHER...NONE.

&&

SYNOPSIS AND MODEL DISCUSSION...PJS
SOUTHCENTRAL ALASKA...EZ
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...AS
LONG TERM...CQ