Brisk Wind Advisory 34, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
527 AM AKST Sun Feb 6 2022

.ANALYSIS AND UPPER LEVELS...

Over the Bering a front is moving slowly south across the
northern Bering. It is producing light snow near the front and
small crafts winds north of the front. A weak mesolow is seen on
satellite northwest of Unalaska with the only sensible weather
being a few snow and rain showers. Across Southwest Alaska colder
air is moving south into the Kuskowim Delta with northerly flow
across the area. Temperatures are currently in the single digits
but just north of the area temperatures near -10 have been
reported. Otherwise low stratus clouds and fog have been reported
across Bristol Bay.

The big story is the wrapped up low pressure system currently east
of Kodiak Island and southwest of Middleton Island. This low is
pushing an occluded front across the northern Gulf. Radar shows
precipitation from south of Middleton Island to eastern Prince
William Sound. Cordova is reporting rain and 36 degrees, while the
rest of the populated areas are dry right now. The only other
significant weather across Southcentral is areas of fog from
Palmer and down the Knik Arm to eastern Anchorage.

&&

.MODEL DISCUSSION...

Models have come into better agreement with the track of the Low
across the Gulf today. Precipitation wise all the models wrap
precipitation towards Anchorage and the MAT valley by this
afternoon into the early evening while the NAM is the only model
not showing this trend> So it is considered the outlier and was
not used for POP or QPF purposes. The next low pressure system
late Monday into Tuesday is looking to take a more westerly track
with the main low moving south of the AKPen and then near Shelikof
Strait and Kodiak Island. The GFS and EC agree well on timing and
location but the NAM is a bit faster and a bit to the east than
these Global models. While the GEM is a bit slower but also takes
a more easterly track on Tuesday.

&&

.AVIATION...

PANC...VFR conditions expected through this afternoon. Light snow
and associated MVFR to occasional IFR conditions may develop by
late afternoon, but most likely this evening into the overnight
hours and will persist into Monday morning. 1 to 3 inches of
accumulation are expected. Light northerly winds will give way to
light southerly winds by early Mon morning (07/12-18z) as a low
pressure system moves towards Cook Inlet.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 through 3/Today
through Tuesday night)...

A surface low has arrived in the northern Gulf, just south of
Cordova. The bulk of short-waves aloft continue to track to the
east of the surface low toward the northeast Gulf coast and
Southeast Alaska. Precipitation out ahead of the surface low has
pushed onshore over southeastern Prince William Sound and spread
northward into the southeastern Copper River Basin. However,
ridging aloft over Southcentral combined with dry offshore flow
in the low levels has prevented precipitation from making it any
further north. This will slowly change through the day as an
Arctic trough digs southward across western Alaska causing the
ridge over Southcentral to lift northward. This will allow
snow to spread northward to Valdez and across the heart of the
Copper River Basin all the way up to the Alaska Range. Warmer air
accompanying the low will continue to produce mainly rain at sea
level in Cordova.

The short-waves over the Gulf will largely exit northeastward
tonight. However, a series of weaker short-waves will enter
Southcentral from the west this afternoon through tonight. The
leading wave coming from the western Alaska trough will advect
Arctic air into Southcentral tonight through Monday. While overall
forcing is weak, it looks to be enough to produce light snow from
the western Kenai to Anchorage and the Mat-Su tonight into Monday.
Accumulation will generally be very light, with a dusting to an
inch for much of this area. The Susitna Valley could see a bit
more accumulation thanks to southerly upslope flow. Precipitation
will diminish across Southcentral Monday, but won't completely
end as cyclonic flow aloft and low level southerly flow maintain
light snow along the south sides of mountain ranges.

A new storm system will make its way up from the Pacific on
Monday, taking a farther west track toward Kodiak Island and the
western Gulf. There is increasing confidence in the low track,
likely continuing north to the Kenai Peninsula and then inland.
This will allow warmer air to advect northward to the Kenai and
Prince William Sound regions, leading to mostly rain near sea
level Monday night into Tuesday. However, there will be a lot of
colder air sitting over the Bering Sea and Southwest Alaska. As
the low heads inland across Southcentral on Tuesday some of this
colder air will wrap around the south side of the low center and
help transition precipitation to mostly snow. This low track will
produce downslope drying for Anchorage and the Mat Valley Monday-
Monday night, but there could be a quick shot of light snow on the
back side. With deep southerly flow behind the low and a fast
moving strong short-wave aloft, this looks favorable for a period
of heavy precipitation across Prince William Sound as well as for
the Susitna Valley. The Susitna Valley should remain cold enough
for all snow, with 6 inches or more of snow likely. Stay tuned as
we work out the details for this next storm system.

Looking beyond Tuesday, the upper level flow will continue to
amplify as a deep and cold upper low drops south across the Bering
Sea. As a result, it looks like another potentially deeper storm
system will track up to Southcentral Tuesday night through
Wednesday.

&&

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

Temperatures will continue to cool today as an arctic air mass
spreads southward and a trough deepens over the Bering and
Kuskokwim Delta. By tonight, lows will dip in the 20s below zero.
Offshore winds will gradually increase, up to 20 mph through the
Kuskokwim Delta where wind chills are expected to reach 40 to 50
below zero Monday and Tuesday mornings. The Wind Chill Advisory in
effect remains on track for the Kuskokwim Delta. While not quite
as cold through the Bristol Bay area, offshore flow will bring
down wind chills to roughly 30 below. While the interior Bristol
Bay and the Kuskokwim Valley may also get bitterly cold wind
chills, winds will be much lighter to nearly calm.

A North Pacific low will track towards the western Gulf and the
AKPen through Monday. Models continue to diverge on the center of
this low, decreasing forecast confidence, especially for the
strength of the resulting wind field and the extent of
precipitation and precipitation type near the AKPen and Southwest
Alaska. Another low will follow close behind on Tuesday afternoon
for another potential round of snow.

&&

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

As an arctic airmass drives southward through the Bering, the
weather will become a little more active. Temperatures will
decrease down into the to near zero by Tuesday morning in the
Pribilofs and into 20s across the Aleutian Chain. Northeast winds
will increase to around 30 kts over the Bering today and spread
south. Expect an increasing threat for heavy freezing spray over
the Bering and spreads southward towards the Aleutians through
Tuesday.

&&

.Marine (Days 3 through 5: Tuesday through Thursday)...

Gulf of Alaska:

A weakening low near Prince William Sound on Tuesday morning will
maintain high end small craft winds with gale force gusts and
seas close to 20 ft south of Middleton Island. As the low moves
inland Tuesday afternoon, expect winds less than 35 kts and seas
less than 20 ft. A well developed North Pacific low with an
associated front approaches near Kodiak Island late Tuesday night.
There is growing confidence that the front will bring easterly
gale force winds along the north gulf coast from Wednesday through
Thursday. During the same time frame, widespread high end
southerly gales with the potential of storm force gusts ahead of
the front will spread across the Gulf and along the Alaska
Peninsula. Seas building above 20 ft are expected as well. Winds
and seas will diminish by Thursday morning. Forecast confidence
with this storm system is moderate to high.

Bering Sea/Aleutians:

A well developed North Pacific low approaches near Sand Point
late Tuesday night into Wednesday morning. Expect north-
northwesterly gale force winds funneling through gaps and passes
along the Central and Eastern Aleutians/Alaska Peninsula through
Wednesday afternoon. Seas will build to 20 ft Pacific side of the
Central Aleutians and on the Bering side as well. As the center of
the low pushes out east into the Western Gulf, winds and seas
will subside by Wednesday evening.

Another North Pacific low will approach near the Central
Aleutians Thursday morning. There is a potential for another round
of gales and elevated seas extending across the same regions and
possibly in the Bering Sea for the rest of day Thursday. However,
there is model uncertainty with the overall track, position, and
strength associated with this storm system. Therefore, forecast
confidence is low.

&&

.Long Term Discussion (Days 4 through 7: Wednesday through Saturday)...

Overall, the latest operational model runs are in decent
agreement with the synoptic scale features in the short term, but
begin to diverge toward the end of the period. An active weather
pattern will be the main theme for the entire southern state as a
series of North Pacific lows will track north of the Western Gulf.
Compared to previous model runs, the first low approaches closer
to Kodiak Island instead going into the Southwest mainland for
late Tuesday night into Wednesday morning. Widespread moderate to
heavy precipitation and gusty winds are increasingly likely as
southerly flow draws warmer air in the Gulf. Most of the warmer
air will be confined along the north Gulf coast with a wintry mix
and/or all rain.

Meanwhile, an Arctic low over the western mainland will bring a
surge of colder air across the Bering Sea and Aleutian Islands.
This will help maintain the potential for snow for these regions,
in addition to the interior valleys and surrounding high
elevations as well. Subsequent lows will continue from Thursday
onward. However, model spread has increased significantly with the
track of these lows and interactions of small to mid scale
embedded systems streaming northward from the Southern Bering Sea.
For now, a wet and active pattern will likely persist as we head
into next week.

&&
.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...Wind Chill Advisory: 155.
MARINE...Gales: 119, 120, 130, 131, 138, 139, 351, 352.
         Heavy Freezing Spray: 160, 165, 179, 180, 185, 412, 414.
FIRE WEATHER...NONE.

&&

SYNOPSIS AND MODEL DISCUSSION...RC
SOUTHCENTRAL ALASKA...SB
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...VR
MARINE/LONG TERM...MF