Gale Warning 190, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
513 PM AKST Mon Feb 21 2022

.ANALYSIS AND UPPER LEVELS...

The large plume of moisture continues to push into Southern
Alaska between the upper level ridge in the eastern Gulf and the
low in the Bering Sea. Warm air is associated with this system,
though the Cook Inlet and Kenai Peninsula has been mostly snow
today with the warmer air aloft being a bit muted. It will
probably take southeasterly winds to reach the surface before
changing precipitation to rain from the snow in Southcentral.
Southwest Alaska is a bit warmer, especially in the Bristol Bay
region. This persistent southerly flow is keeping precipitation
mostly rain with widespread low clouds and fog especially along
the coast.

&&

.MODEL DISCUSSION...

Models remain in good synoptic agreement through most of the
week. The main item of note is that the NAM is a bit later
bringing southeast winds into Anchorage this evening and keeping
the northerly surface flow around a little longer which is keeping
more snow in the area. The note in the last discussion about the
NAM hinting at a little more southwesterly flow seems to be right
on as that is helping to keep all downsloping out of the Cook
Inlet region earlier today.

&&

.AVIATION...

PANC...Winds shear will persist until this evening when the gusty
southeasterly winds descend to the surface. At this time it looks
like wind gusts should increase to 25 to 30 kt with a few higher
gusts between 06Z and 10Z. Until the winds switch the precipitation
type should remain snow, but warmer air in conjunction with these
winds will switch any remaining precipitation to rain at that
time.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Tonight through Thu
afternoon)...

A strong upper level ridge remains anchored over the North Pacific
while a strong upper level shortwave trough continues moving
northeastward across the Alaska Peninsula. In between the two
deep, moist, southwesterly flow continues advecting moisture up
the Cook Inlet region. This is resulting in snow falling
practically everywhere. A Winter Storm Warning remains in effect
for the Susitna Valley where an additional 6 to 12 inches of snow
is expected between now and midday Tuesday with highest amounts
across the northern Susitna Valley. Around the Willow area an
additional 3 to 5 inches is expected. Snowfall rates are expected
to increase even further as the upper level shortwave trough moves
closer to the region increasing the lift out ahead of it.
Therefore, the worst of this system may yet be ahead for the
Susitna Valley as we head into the evening and overnight hours.

Kenai Peninsula: Warmer air has been slowly oozing northward along
the interior of the Peninsula west of the Kenai Mountains. As of
this writing...Kenai and Soldotna to Nikiski remain all snow where
couple to several inches may have already fallen. An additional 2
to 4 inches is expected through the evening hours with the highest
amounts near Nikiski. Soldotna is expected to change to rain
sometime this evening with Kenai right on the edge where
uncertainty still remains as to how much warm air makes it in and
if it changes to rain. Nikiski where the deeper cold air remains
should remain mostly snow.

Anchorage Bowl and Mat Valley: Light to at times moderate snow
continues to fall which is expected to continue into the evening
hours. For Anchorage, expecting the Turnagain Arm wind to bend
into the bowl bringing gusts upwards of 40 mph especially south
to west Anchorage. The upper Hillside and Turnagain Arm may see
gusts as high as 70 mph this evening and overnight. Winds are
expected to peak around midnight. Temperatures may rise into the
upper 30s or low 40s overnight through Tuesday. Any snow will
largely change to rain once the winds come in. Same is true for
the Mat Valley including Palmer- Wasilla area where the Knik River
Valley wind will warm temperatures above freezing to change snow
to rain. Hatcher Pass will remain cold enough for all snow with an
additional 18 to 24 inches with additional QPF of 1.5 to 2 inches.

Copper River Basin and Prince William Sound: Snow will continue
overspreading the area through this evening with the steadiest
and heaviest snow overnight into Tue morning. Snow tapers off
by midday Tuesday though some light snow may remain around the
Valdez area through dusk Tuesday. Up to a foot of snow is
expected for Valdez and Thompson Pass area.

Next, the upper level trough moves from west to east across
Southcentral through the day Tuesday ending precipitation from
west to east. Upper level heights build across Southcentral
Tuesday night leading to quieter and drier weather. Then attention
turns to yet another system that will move northward Wednesday
through Thursday, but is expected to largely be a downslope
situation for many of the population areas. Thus, the bulk of
precipitation will be along the coast while interior areas remain
dry.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 through 3 - Tonight
through Thursday night)...

An active weather pattern continues for Southwest AK as broad
frontal systems combined with mid to upper short-wave troughs
advance from the North Pacific and the Eastern Bering into the
Southwest the next few days. Precipitation from the current
system will diminish tonight, with just some light snow lingering
over interior areas through Tuesday. Ridging aloft will bring
brief relief to Southwest as early as Tue afternoon into Tue
evening before the next frontal system from the south of eastern
Aleutians moves into Bristol Bay Tue night. Warm tropical moisture
will once again stream northward, leading to warming temperatures
and a transition from snow to rain for much of the region.
Wednesday in particular looks quite warm and thus expect rain
to become the dominant precipitation type.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 through 3 -
Tonight through Thursday night)...

A very active weather pattern will persist for the
Aleutians/Bering Sea the next three days as one low in the
central Bering gets replaced by another in the western Bering.
In general, rain will favor areas from Unalaska east and snow or
mixed precipitation is more likely to the west with colder
temperatures aloft. Rain is expected to continue along the Alaska
Peninsula and eastern Aleutians as a shortwave coupled with deep
southerly flow moves over the area. Meanwhile, a gale force front
extending from a Kamchatka low will move slowly east across the
Western and eventually Central and Eastern Aleutians. Expect rain
along the front with convective snow showers behind as cold air
wraps around the low. Early Wednesday the front will combine with
a north Pacific low and upper level shortwave to produce some
heavier rain before the low shifts north into the Bering Sea and
returns the region to a more showery regime.

&&

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

Gulf of Alaska:
A barrier jet is expected to set up along the Gulf coast
beginning Wednesday night that will strengthen to gales and
possibly storm force through at least Friday as a low enters the
Gulf on Thursday and tracks north. As this low moves inland,
westerly winds will return and diminish the coastal barrier jet
Saturday. Seas build through late Friday night to around 20 feet,
but expect seas to go back down to around 10 feet Saturday night.

Bering Sea/Aleutians:
A passing low northward across the Aleutians and the Bering sea
will keep southerly flow across the region through Friday when
winds will become westerly and another low approaches from the
western Gulf toward the AKPen. Winds will return to generally
southerly flow again Saturday. Seas to about 10 feet on the Bering
side and generally 10 to 15 feet on the Pacific side through the
last half of the week.

&&

.Long Term Discussion (Days 4 through 7: Friday through Monday)...

Overall, the latest operational model runs are in decent agreement
with the synoptic scale features in the short term, but increasing
uncertainty emerges toward the end of the period. A large upper
level ridge extends northwestward from the eastern Pacific into
the Arctic. Meanwhile, a negatively-tilted trough extends from the
western to central Bering Sea to the central Pacific. This synoptic
setup will set the stage for a southerly flow pattern to persist
possibly through early next week.

On Friday, models are suggesting a shortwave and developing
surface low south of the Alaska Peninsula/Kodiak Island streaming
northward into the Gulf. With southerly flow and warmer air aloft,
most of the precipitation will fall as rain along the southern
Alaska coast and parts of the interior valleys. The exception will
be for the surrounding mountains as precipitation type is
expected to be snow as colder air remains in place. However,
moisture may be limited in the Western Kenai Peninsula, Anchorage,
and the Matanuska Valley as 850 mb winds shows a southeasterly
component flowing across the Chugach Mountains, which would result
in downslope drying.

Out west, broad cyclonic flow with embedded shortwaves will
maintain a cool and wet pattern for the Bering Sea and Aleutian
Islands through the end of the weekend. However, model spread has
increased significantly with the small to mid scale embedded
systems streaming northward from the southern Bering Sea, though
minimal impact is expected. By early Monday, a gale force front
extending from a Kamchatka low will move slowly east across the
Western/Central Aleutians.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...Winter Storm Warning 145.
         Winter Weather Advisory 121 152.
MARINE...Gale Warning 119 125 130 138 139 141 155 160 165 173
                      174 175 176 177 178 180 181 185.
FIRE WEATHER...NONE.

&&

SYNOPSIS AND MODEL DISCUSSION...EZ
SOUTHCENTRAL ALASKA...MV
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...CB
MARINE/LONG TERM...VR/MF