Gale Warning 255, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion...UPDATED
National Weather Service Anchorage AK
951 PM AKDT Sun Mar 19 2023

.ANALYSIS AND UPPER LEVELS...

The high amplitude trough over the Southern Mainland that has
been the dominant weather feature over the past week is shearing
apart from north to south as a strong jet streak and attendant
hurricane force low move east from the Western Bering this
afternoon. High Wind Warnings are in effect from Adak Island west
towards Shemya, in addition to the Pribilof Islands. A Blizzard
Warning is also in effect for the Kuskokwim Delta coast as the
strong front moves onshore later tonight. Over Southcentral, quiet
weather has taken hold of the region, with sunny skies and
warming temperatures being enjoyed by many underneath the March
sunshine. The exception to this is the Eastern Kenai Peninsula,
where a small area of low pressure in addition to cold air aloft
has continued a showery regime and overcast skies. Some of these
high clouds have also made their way over the Kenai Mountains and
into the Anchorage area.

&&

.MODEL DISCUSSION...

Overall models are in excellent agreement in the short term. The
NAM solution does indicate a splitting of the low over the Kenai
Mountains late Tuesday night as it forms along the triple point,
but this solution is an outlier with the remaining solutions
moving the low south of the Kenai Peninsula. This would have some
effect on the wind field, but overall the difference is minor.

&&

.AVIATION...

PANC...VFR conditions will persist. Light and variable winds will
persist through the morning hours Monday before a Turnagain Arm
wind moves in around sunrise.

&&

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

A compact low continues to push north over the northern Gulf this
evening, with the center now about halfway between Middleton
Island and Seward. While this low is lacking in upper level
support, it has been interacting with an upper trough axis sitting
over Cook Inlet, where upper level divergence is combining with
moisture influx from the small Gulf low to produce weak bands of
light snow across the western Kenai Peninsula. Otherwise, most of
the snow associated with the low will stay towards the opposite
coast of the Kenai Peninsula between Whittier and Seward this
evening. All of the above activity should die down later tonight
as the low moves into the coast near Seward and quickly shears
apart.

Looking towards Monday, an impressive low moving over the Bering
Sea will push it's front into the the southwest corner of the
Gulf, sending rain and snow into Kodiak Island by the early
afternoon. Southeast flow will begin to strengthen over the
remainder of Southcentral out ahead of the frontal wave and
deepening upper trough approaching from the west, with gap winds
expected to begin to pick up through the Kenai Mountains and
western Chugach Range, namely along the Turnagain Arm. These winds
will strengthen through Monday night as a new low forms at the
frontal triple point north of Kodiak Island and quickly deepens
with support from the amplifying upper trough ejecting into the
Gulf. Snow will spread back into the eastern Kenai Peninsula and
Prince William Sound region as well, especially where aided by
upslope flow near the coast. Most of the Mat-Su Valleys and
Anchorage areas will stay dry through early Tuesday due to the
strong cross-barrier flow and downslope drying continuing ahead of
the low.

On Tuesday, the Gulf low will weaken as it continues northeast
towards Prince William Sound as the upper trough continues to lift
northeast towards the Copper River Basin. There is some potential
for a short burst of snow to follow along the best upper forcing
near the trough axis, with a band possibly organizing over the
western Kenai Peninsula during the morning and advancing swiftly
north past the Mat Valley and Anchorage areas by the afternoon.
However, any snow accumulation across these areas would remain
very minor, with only a quick hour or so of snow pushing past any
given location before the trough lifts up into the Alaska Range
Tuesday evening. A somewhat stronger low will enter the Gulf on
Wednesday, likely supporting gale force winds over much of the
open Gulf waters. Once again, this is shaping up to be another
mainly coastal event for heavier rain/snow, including most of the
Prince William Sound region, eastern Kenai Peninsula and across
Kodiak Island.

&&

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

Generally calm conditions have been observed over Southwest
Alaska today. A dissipating low from the Gulf of Alaska has
petered out over interior Bristol Bay, leaving scattered clouds
stretching northward into the Lower Kuskokwim Valley. The
Kuskokwim Delta meanwhile enjoyed a temporary period of clear
skies. All of this will gradually come to an end through
tonight/tomorrow morning with the arrival of a front into
Southwest. Of immediate concern is the expectation for blizzard
conditions to develop from Nunivak Island into the Kuskokwim Delta
tonight into Monday morning. A blizzard warning is in effect for
winds gusting as high as 60 mph along coastal areas with blowing
snow to reduce visibility down to one quarter mile. Gusty winds
and snow will gradually extend southward into northwestern
portions of Bristol Bay Monday morning as well. A winter weather
advisory has been issued for Togiak and areas north and west,
including the cities of Platinum and Goodnews Bay, for snow and
blowing snow. Accumulating snow ranging from 3 to 5 inches will be
met by increasing southeasterly winds gusting up to 35 mph on
Monday. Which should promote blowing snow and reduced visibilities
down to one half mile at times.

High pressure is forecast to spread across Southwest Alaska
through Tuesday with a break from winds and precipitation. An
Aleutian low will then move into Southwest late Tuesday into
Wednesday with showers and winds to return to the region.

&&

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

A hurricane force low is skirting just north of the Western and
Central Aleutians this evening with widespread gales everywhere
else. Cold air advection wrapping around the backside of the low
is producing strong westerly winds gusting to 65+ knots.
Unsurprisingly, high wind warnings are in effect from Shemya to
Adak to Saint Paul. Shemya's winds have likely peaked over the
past hour with multiple observed gusts to 75 mph. Adak, not to be
outdone, reported gusts to 77 mph around 4pm AKDT mph and could
see higher gusts through the next few hours. As the low continues
tracking off to the northeast through tonight, a swath of elevated
winds and seas will accompany the low across the Pribilof Islands
through the morning hours on Monday. Seas to over 30 feet will be
possible within the core of the strongest winds. Winds will
ultimately move into Kuskokwim Delta coast late Monday as the low
continues to fill in and weaken, while seas diminish near the ice
edge to the east of the Pribilofs earlier in the day.

Forecast uncertainty begins to decrease Monday into Tuesday.
Models are depicting a shortwave trough digging across the
Aleutian Chain late Monday into Tuesday morning. With it will come
renewed shower chances, mainly snow, and gusty conditions as the
current hurricane force low is expected drag widespread minus six
degree 850 mb temperatures and colder across the entire Bering and
well south of the Aleutians through early next week. A ridge of
high pressure is then forecast to move into the western Bering on
Wednesday with warming temperatures for the Western and Central
Aleutians.

&&

.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...High Wind Warning: 191 195 187
         Winter Weather Advisory: 161
         Blizzard Warning: 155
MARINE...Hurricane Force Wind Warning: Central Bering, Western Aleutians
         Storm Warning: Western/Eastern Bering, Central Aleutians,
                        Pribilof Islands Gale Warning: Alaska Peninsula
                        Bering Side, Eastern Aleutians, Kuskokwim Delta
                        Coast, Saint Matthew Island
Heavy Freezing Spray Warning: Kuskokwim Delta Coast

FIRE WEATHER...NONE.

&&

SYNOPSIS AND MODEL DISCUSSION...CJ
SOUTHCENTRAL ALASKA...AS
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...BL
LONG TERM...DN