Hurricane Force Wind Warning 1, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
600 AM AKST Sun Feb 12 2023

.ANALYSIS AND UPPER LEVELS...

A broad upper-level longwave continues to stretch across much of
Alaska, that has created a synoptic circulation over northern
Southwest Alaska and a surface low set-up in the Central Gulf of
Alaska. This pattern has also produced several small closed
circulations near the surface along the southern edge of the
Aleutian Chain. The presence of these disturbances has promoted
unsettled conditions, with snow showers across much of Southern
Alaska. A mix of rain/snow is still found along the Prince William
Sound due to warmer air coming in from the Southeast.

This pattern is expected to linger through Sunday morning, when
the low over the Gulf will begin to shift eastward, easing the
snow/rain found across Southcentral. Similarly in Southwest
Alaska, snow showers will continue before easing off by Sunday
evening. Precipitation in the Chain will persist, and will be
reinforced by a North Pacific low by Sunday afternoon. This low
will drift eastward, pushing a swinging front first into the
Eastern Aleutians by Monday morning, then into Southwest Alaska by
Tuesday morning. By Tuesday time, a new low will enter the
Western Aleutians, maintaining the consistent disturbed pattern
across Southern Alaska into the beginning of the next work week.

&&

.MODEL DISCUSSION...

Synoptic agreement amongst the deterministic models remain fair,
with some slight discrepancies regarding the track and associated
impacts of the surface low in the Gulf. Overall forecast
confidence is moderate. Lower agreement in the short-term again is
mostly linked to the lingering surface low in the North Gulf.
Areas of minor convective activity also make it difficult to
expect where localized snowfall maxima will be. Agreement between
models improves by Monday morning as the North Pacific low
approaches the Bering, with little discrepancies seen regarding
its track and impact. However, model solutions then again diverge
by Monday afternoon, specifically regarding timing the eastern
progression of the front pushing along the Chain into Southwest
Alaska.

&&

.AVIATION...

PANC...Predominant IFR vis with 1-3 SM in light snow and MVFR-
VFR cigs through the TAF period. Prolonged periods of LIFR
vis/cigs are possible this morning as convective bands move
through. LIFR VIS and heavier snow bands are possible to return
later today as systems move through the area until Sunday
night/Monday morning. Steady northwest flow throughout the period
with gusts possible Sunday night.

&&

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

Active weather continues through the rest of the this weekend.
The low over the northern Gulf is begin to move eastward today.
Snow showers will taper off but could individual waves may bring
periods of snowfall along the coast near the Copper River Delta.
Meanwhile, a trough behind the low will swing across Southwest
Alaska into the western Gulf later today. Cold air is beginning to
advect from the west and will continue to usher east throughout
the day. Winds will also accompany the cold air, gusting as high
as 70 kts through the Barren Islands. This raises extreme freezing
spray hazards along Shelikof Strait and the Barren Islands.
Westerly winds are expected to push into Kachemak Bay and bring
visibility in blowing snow to a quarter mile or less later this
morning into tonight. A Marine Weather Statement and Blizzard
Warning was issued and remains on track. Many wind gap prone
locations, such as Whittier, Seward, Valdez, and Thompson Pass
will also experience an increase in outflow winds Sunday into
Monday.

Snow has been persisting through the Anchorage area, northern
Kenai Peninsula, and the Matanuska and Susitna Valleys. This will
likely continue through today and taper off Monday morning.
Localized heavy banding is possible for the Anchorage area late
afternoon through tonight. There is some uncertainty in where the
heaviest banding will set up along Anchorage and also with the
spatial extent northward to Talkeetna and southward to Kenai.

The next system will shift winds southeasterly Monday night and
allow temperatures to briefly warm along the Gulf coast for
Tuesday and Wednesday. The brief break from snow on Monday
afternoon will end by Tuesday when the trough lifts northeastward.
Under this highly amplified pattern, expect active weather to
continue.

&&

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

A shortwave trough extending across Southwest Alaska will keep
the light, lingering snow showers over Bristol Bay, the Kuskokwim
Valley, and portions of the Alaska Peninsula this morning.
Snowfall should taper off into the late morning/early afternoon
hours as the wave rotates off to the east. Cold air remains in
place over the Mainland, with daytime temperatures in the single
digits today, sub-zero on Monday, and overnight temperatures
dropping to a frigid 20 below tonight. There will be a weak
warming trend mid-week as a Bering front moves towards the
Southwest Coast, as well as another round of snow showers.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 and 2)...

A storm force low makes its way towards the Central Aleutians
today. The associated front tracks into the Bering Sea this
evening, passing an area of storm force winds over the Central
Aleutians, as well as a band of snow on the leading edge of the
front. Snow is expected to quickly transition to rain along the
Aleutian Chain as a mass of warmer air moves in immediately behind
the front. By Monday morning, the front pushes towards the
central Bering Sea. Gusty northerly winds and periods of heavy
snowfall will create blizzard conditions for the Pribilof Islands
beginning Monday morning; a Blizzard Warning has been issued for
the area. Due to the track of the low as it moves eastward along
the Chain, strong winds and snowfall will continue to wrap around
the low, keeping the Pribilof Islands locked into blizzard
conditions through Monday and into Tuesday morning. Total snow
accumulations are expected to be between 7-9 inches with wind
gusts to 60 mph possible. Additionally, strong winds will continue
across the Central Aleutians, and cold air wrap around will allow
for another round of snowfall on Monday night. There may be brief
periods of blowing snow at times but should remain above advisory
criteria.

&&

.LONG TERM FORECAST (Days 4 through 7: Wednesday through
Saturday)...

A highly amplified pattern is expected next week with a series of
strong lows forecast to track across the region. The run to run
continuity with the models is resulting in low forecast
confidence this forecast period. But there are a few things to
glean. The Gulf of Alaska looks active. Out west, a low near
Kamchatka, potentially as deep as 944 mb, pushes a storm force
front into the western and central Aleutians on Wednesday. The
front sweeps to the eastern Aleutians by Thursday. Model uncertainty
amplifies with time. Generally expect a series of short-waves
embedded in the long-wave pattern to traverse the Bering Sea
region. This will result in continued active weather from the
Aleutians to southern Alaska. The overall progressive upper level
flow will maintain a cold enough airmass to support primarily snow
over southern Alaska.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...Blizzard Warning 121, 195.
MARINE...Heavy Freezing Spray Warning 121 129 130 131 132 136 137
									  138 139 141 150 160 165 179
									  180 185 412 414.
		 Storm Warning 120 130 131 175 176 177 178 411 413 414.
		 Gale Warning 119 121 132 136 137 138 139 141 150 155
					  165 170 171 172 173 174 179 351 352 412.
FIRE WEATHER...NONE.

&&

SYNOPSIS AND MODEL DISCUSSION...CL
SOUTHCENTRAL ALASKA...VR
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...KM
LONG TERM...PS