Gale Warning 256, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
510 AM AKDT Mon Mar 20 2023

.ANALYSIS AND UPPER LEVELS...

The pattern remains amplified as an upper level trough extends
across the Bering/Aleutians and Gulf of Alaska with a weak
transient upper level ridge over the Kuskokwim Valley and Bristol
Bay. A front is currently moving eastward across the Kuskokwim
Delta and Bristol Bay and is bringing snow to the area.

Closer to the surface, radar and observations show snow across the
Kuskokwim Delta and Bristol Bay from the aforementioned front.
Radar also shows showers moving northward from the Gulf of Alaska
into the Chugach and Kenai Mountains.

&&

.MODEL DISCUSSION...

Guidance remains in good agreement with respect to the placement
and intensity of synoptic scale features. The biggest challenge
continues to be resolving mesoscale local effects.

&&

.AVIATION...
PANC...VFR conditions will persist for this TAF package. There is
a chance for southeasterly Turnagain Arm winds after 20th/20z.

&&

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

The remnants of the low that moved form south to north across the
Gulf are now pushing some snow showers over the north Gulf coast.
Some clouds are also tracking across the rest of the Kenai
Peninsula due to this old low. The rest of Southcentral is under
mostly clear skies ahead of the strong front that is approaching
the region from the west. This front will move over Kodiak today
and initially bring snow and gusty southerly winds. The big
question is how much warm air will make it over the Islands to
turn precipitation to rain. Farther south areas like Akhiok and
Old Harbor should turn to rain later this afternoon but KOdiak
City will be right on the cusp of the rain/snow line this evening
when the warmest air arrives. This front will then develop a
triple- point low over the southern Kenai Peninsula tonight which
will track due east along the northern Gulf coast. This will keep
the warmer air south of the land areas so snow is expected for the
Prince William Sound region overnight into Tuesday morning.

Southeasterly winds off of Turnagain Arm are expected into
Anchorage by this afternoon with the Matanuska Valley seeing
increasing easterly winds as well. The winds should diminish
after midnight as the cross barrier flow eases and the upper
level wave moves overhead Tuesday morning. There is a chance for
some light snowfall over Anchorage and the Matanuska Valley
Tuesday morning with this upper level wave, but it should not
amount to much.

The next low will then move into the Gulf from the southwest
Tuesday night into Wednesday. This will bring some more Gale force
winds to the Gulf and precipitation to the areas on the Gulf
coast. This low could be an interesting one for Wednesday into
Thursday for the Cook Inlet and MatSu areas. The cold air
advection from the southwest combined with the 500 mb trough in
southwest Alaska moving slowly eastward gives the potential for
some more accumulation snowfall in these areas.

&&

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

A deep low in the northern Bering Sea is pushing a strong front
along the Southwest coast this morning. Blizzard conditions are
ongoing along the Kuskokwim Delta coast, with winds gusting as
high as 65 mph and heavy snow, despite temperatures hovering near
30 degrees. Conditions are beginning to improve on Nunivak Island
behind the front and will continue to do so from west to east as
the front pushes inland rather quickly. This will also bring the
arrival of deteriorating conditions to locations along the
northern Bristol Bay coast. As a result, the Winter Weather
Advisory has been extended eastward to include Dillingham.
Southeasterly winds are not expected to gust as high for Bristol
Bay, reaching only around 35 mph this morning, with visibility
dropping to near half a mile due to blowing snow, before
conditions improve as the front continues eastward. 2 to 4 inches
of snow are expected through this afternoon as a result of the
front. Snow will turn showery in the wake of the front, with
temperatures rising to near and above freezing most places,
limiting any snow accumulation later in the day. Steadier snow
will linger longest within interior Bristol Bay, especially near
Iliamna before the front finally exits the region tonight. Then,
skies clear somewhat and allow temperatures to fall with a quick
transient ridge tonight.

Tuesday morning, another round of snow showers arrives for
Southwest Alaska with a much weaker low tracking across the Alaska
Peninsula. The greatest snowfall totals will be focused within
the Kuskokwim Delta and western portions of Bristol Bay (as well
as on the Alaska Peninsula), where one to two inches of snow will
be possible through Tuesday night. The low intensifies as it
enters the western Gulf, drawing much colder air across the
eastern Bering Sea and Southwest Alaska Tuesday night. This will
lead to cooler temperatures region-wide for Wednesday, with snow
showers likely to persist along the Alaska Peninsula and only
light scattered snowfall across portions of the mainland
Southwest.

&&

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

A strong low in the northern Bering Sea is bringing high winds to
the Pribilof Islands this morning. Seas over 30 feet will
accompany the strong winds on the south side of the low today
before it exits northward and winds diminish. In its wake,
widespread snow showers will move in across the Bering Sea, with a
particularly enhanced area associated with a weak low expected to
track eastward along the Aleutian Islands this afternoon through
Tuesday night. Gusty winds are also expected in association with
this low, and winds through the eastern Aleutians have the
potential to gust as high as 75 mph on Tuesday afternoon, though
confidence associated with this relatively weak feature is low at
this time. Then, a broad, flat ridge of high pressure is expected
to enter the western Bering on Wednesday with warming
temperatures for the western and central Aleutians as westerly
flow begins to predominate. Snow showers are expected to continue
into midweek further north within the central and eastern Bering
Sea.

&&

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

The extended forecast looks to remain active through the Gulf of
Alaska and Southcentral Alaska at least through Friday. While
guidance exhibits agreement somewhat on the bigger synoptic
features, namely the negatively tilted trough extending from
Siberia and through Southern Alaska, there remains questions on
the ultimate tracks of lows within this pattern. Guidance has
trended weaker with a central Gulf low Thursday, but there are
still disagreements with the ultimate track. The 12z Canadian and
12z ECMWF guidance are the most progressive in moving the low
southeast to the North Pacific, while the 12z GFS lingers the low
longer in the Gulf through Friday night. This is in part due to
the negatively tilted trough on the Canadian and ECMWF guidance
pinching off further to the south while a ridge tries to build in
around the upper Pan Handle region. The trough on the GFS stays
open longer due to little ridging trying to build in, and another
shortwave drops in from the northwest to the Gulf Friday. The 12z
GFS ensembles and Canadian ensembles, to some degree, agree with
the 12z deterministic GFS. However, the 12z ECMWF/ensembles, and
12z deterministic Canadian insist on cutting off the trough with
the Pan Handle ridge. All-in-all the eastern Kenai Peninsula and
the northern Gulf Coast, including Prince William Sound, still
look to have the best chances at precipitation through at least
Friday. It still remains up for debate if precipitation chances
will linger past then. Guidance, both deterministic and ensembles,
then hints at a pretty strong ridge moving over the southern
mainland Saturday and Sunday with potentially quieter weather.

Out west, Southwest Alaska, the central Bering Sea, and the eastern
Bering remain active through Saturday morning as a series of
frontal systems moves eastward to the southwestern coast. Each
frontal system will bring precipitation chances and gusty winds
for the central/eastern Aleutian Chain, Bristol Bay, and the
Kuskokwim Delta. The strongest of these systems appears to be for
Friday. However, there are disagreements on the eastward extent
of this front extending off a low near Kamchatka. Right now, the
GFS appears to be an outlier with the front remaining well off
shore in the Bering, while the Canadian and ECMWF have the front
extending to the southwest coast and providing precipitation
chances through Saturday. While the western Bering/Aleutian Chain
remain mostly benign through the long-term, the cold front of the
aforementioned Kamchatka low looks to sweep through the western
and central Bering and Aleutians Friday through Sunday and
potentially reaching the southwestern coast Sunday evening.
However, there are disagreements both on the strength of the front
and the exact timing and eastward progression of it. At least
gale-force winds, with potentially pockets of storm-force winds,
look to accompany this front as it makes it to the western Bering
for Friday.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...Blizzard Warning 155.
High Wind Warning 195.
Winter Weather Advisory 161.
MARINE...Storm Warning 774 775 766 412 414.
Gale Warning 755 759 770 771 772 773 776 777 778 780 781
782 783 784 785 786 787 763 764 765 767 411 413.
FIRE WEATHER...NONE.

&&

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