Heavy Freezing Spray Warning 62, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
530 AM AKST Mon Feb 8 2021

.ANALYSIS AND UPPER LEVELS...

Persistent upper level ridging continues today and tomorrow
across the Gulf and Southern Mainland. A strong upper level Arctic
low develops over the North Slope on Tuesday and tracks
west/northwest through Wednesday. This ultimately will flatten
the ridge briefly as it passes and end up pulling the high
pressure center north over the Southcentral Mainland by Wednesday
evening. Out west, high pressure remains over much of the Bering
through late Tuesday night, keeping the front off a Kamchatka low
confined to the Western Bering. A North Pacific low moves just
south of the Aleutian Chain Wednesday morning, tracking a series
of upper level shortwaves across the Aleutian Islands. The main
front pushes towards the Southern AKPEN early Thursday morning,
which may aid in forcing out the ridging over the Southwest
Mainland. This could result in a more active weather pattern for
the region.

&&

.MODEL DISCUSSION...

Models are in good synoptic agreement for the short term. The
upper levels have come into much better agreement as well compared
to yesterday. The NAM is now conforming towards the
GFS/EC/Canadian solutions by incorporating a strong upper level
Arctic low over the North Slope. At the surface, models agree
relatively well overall, with the main discrepancies being withing
a strong North Pacific low south of the Aleutians on Wednesday. A
secondary low developing within the longwave trough extending to
the east of this parent low is hinted at across all solutions.
However, model spread is still too large to discern when and
where this secondary low will form.

&&

.AVIATION...
PANC...VFR conditions and light winds will persist. Periods of
patchy fog are possible throughout this morning but should
subside by this afternoon.

&&

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

Winter retains a firm grip on the weather across all of
Southcentral for at least the next 2 days, as high pressure
remains in full control over the area. A drier air mass, which as yet
hasn't proven itself to be significantly colder, is filtering
into the area from the northeast this morning. This was expected
to result in temperatures falling even further from the Copper
River Basin through Thompson Pass. However, this has yet to
materialize. In fact, the winds associated with that air mass have
caused temperatures to rise early this morning, with Gulkana now
north of 10 below, and Thompson Pass above zero. Thus, the
bitterly cold wind chills in Thompson Pass have failed to
materialize (not that the 20 to 25 below wind chills they are
seeing are a tropical day by any stretch). With the Copper Basin
not cooling either, it appears all of the model guidance is
unanimously too cold compared with what's actually occurring.
Thus, the Wind Chill Advisory for Thompson Pass has been
cancelled, considering the trend of at least the past 3 days of
the model guidance being too cold.

Elsewhere, the primary forecast challenge remains the movement of
the fog and low stratus around portions of the area. While it is
much less widespread than it was this time yesterday, it is still
temporarily dropping visibilities in some of the affected
locations. As the winds pick up with the advancing drier air mass,
it is expected that all areas should scour out the fog during the
day today. The winds should remain elevated overnight for most
areas, though of course anywhere that the winds can calm down
should see temperatures plummet to potentially their coldest
readings of the winter overnight tonight.

A modest warmup will begin on Tuesday, with late week temperatures
returning back towards seasonal normals. This will occur in part
due to increasing cloud cover from a lee-side inverted surface
trough that develops over the Gulf, then drifts westward towards
the mainland, eventually combining forces with a very slowly
moving front coming in from the Bering. The front adding moisture
to the inverted trough Tuesday night should be enough to bring the
next chance of snow to much of Southcentral. Certainly nothing
earth-shattering is expected, but a general 1-3 inches for much
of the Cook Inlet region, with a bit more for the Susitna Valley
and the Kenai Mountains are expected into the day on Wednesday.
The inverted trough will be fully absorbed into the front by
midday Wednesday, which should end the snow from east to west.

Considerable uncertainty remains for Kodiak Island Wednesday night
however. This is primarily due to large differences as to where
the very slowly moving front will be by then. Most of the model
guidance has at least some precipitation moving in off the Gulf
into Kodiak Island, but it is far from unanimous. Generally
speaking the closer the heavier precipitation is, the warmer, and
thus the more likely to be in the form of rain, whereas if the
bulk of the moisture stays with a front much further south and
west from the island, the more likely the moisture that does come
into Kodiak is in the form of snow. Considering how cold the
present air mass is, the position of the front will be the primary
determining factor as to whether Kodiak could be cold, dry, but
cloudy, a prolonged light snow, heavier snow, or a cold rain by
Thursday. With all of those options currently on the table, that
looks to be the best chance of impactful, hazardous weather
anywhere in Southcentral through midweek. Stay tuned.

&&

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

Another dry day is in store for much of Southwest Alaska today as
the upper level ridge remains over the region. The main thing
today will be breezy conditions with sustained northeast winds of
15 to 25 mph with the cold temperatures. This will create very
cold wind chills in the teens below zero (especially across the
Kuskokwim Delta) to single numbers above zero throughout the rest
of Southwest. Some high clouds associated with a weak frontal
system off the coast of Southwest will remain fairly stationary
throughout the day keeping any snow with this over the ice/open
water in the Bering. Nunivak Island especially the western side
has the best chance to see any snow out of this front.

Tonight into Tuesday morning, the pressure gradient tightens some
across Southwest, resulting in wind speeds increasing another 5-10
mph from where they are now. Cold air advection overnight will
result in temperatures falling even further tonight especially for
the Kuskokwim Delta into the single numbers below zero with the
wind. This will result in wind chills between -25 to -35 below
zero.

Another frontal system is poised to move into Southwest beginning
as early as Tuesday morning or not until Tuesday
afternoon/evening. There still remains some considerable
uncertainty on the timing of this front even though we are almost
inside 24 hours. Model guidance has just been having a real tough
time with handling the individual features in this pattern. The
one area of high confidence is for overnight Tuesday into
Wednesday when snow is expected to overspread much of Southwest. A
couple to several inches of snow is possible from this event
along with the wind and reductions in visibility. The best
confidence for reductions in visibility to 1/2 mile at this time
appears to be along the Kuskokwim Delta Coast and Nunivak Island
for Wednesday morning through Wednesday evening, though,
uncertainty remains. As a result, no product will be issued just
yet with this package as things can still change.

&&

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

A frontal system currently between the Pribilofs and Nunivak
Island will remain fairly stationary throughout the day while
weakening. It won't make any progress further east due to the
strong Arctic high pressure in place across the Alaska Interior.
If anything, the front will retrograde back to the west some.
Dutch Harbor will continue to remain in the unsettled pattern as
well as Cold Bay and Sand Point as another system moves up from
the south and brings more rain to the area especially for
Tuesday. This rain is not expected to be nearly as heavy as it was
in recent days.

A narrow upper level ridge remains in place across Adak and Atka
keeping them dry with even some sunshine expected today. Another
frontal system in place to the west of Adak but east of Shemya
put on the breaks overnight as the pattern remains very stagnant
and not much is able to push eastward. This front also is expected
to retrograde back to the west and bring winds and mostly rain
but some snow might mix in back towards Shemya. Yet another
frontal system is expected to move northward and phase with the
one currently in place resulting in a stronger front with the
potential for storm force winds across the far westernmost
offshore zone in the Bering tonight.

Lastly, yet another storm system as the Bering remains very active
will move north Tuesday afternoon and evening and absorb the
energy from the front to the north. This will result in an even
stronger storm system (~950 mb) with storm force winds for the
Bering and Southern AKPEN marine waters with the gale force winds
widespread. This storm will keep the Bering Sea unsettled for
several days. It will also pass off some its energy to the front
that has remained stationary for several days now and basically
reinvigorate it bringing even more precipitation to the eastern
Aleutians and AKPEN Wednesday evening into early Thursday though
uncertainty remains on the timing. Basically, the Bering will stay
very active!

&&

.MARINE (Days 3 through 5: Wed through Fri)...

Bering Sea: Models are coming into better agreement with a deep
North Pacific low on Wednesday positioned south of the western
Aleutians. The associated front will bring widespread high end
gale force winds stretched across the entirety of the Bering Sea
through Thursday afternoon as the low center lifts towards Adak.
There is some uncertainty of where the strongest core of winds
will be located, but there is a chance to see sustained storm
force winds Wednesday and Thursday across the Bering, which when
then start to slightly weaken on Friday.

Gulf of Alaska: There is good agreement of a front over the
western Gulf on Wednesday, which will increase to gale force
strength and persists through Friday morning. By Friday afternoon,
winds will decrease to small craft advisory level and continue to
weaken through the night.

&&

.LONG TERM FORECAST (Days 4 through 7: Thu through Sun)...

A cool but relatively quiet pattern is in store for the Alaskan
mainland as surface and upper level high pressure extend across
the area. There is good ensemble agreement that higher pressure
will be over the Alaskan interior and lower pressure off shore in
the Bering and Gulf, thus the flow will be offshore and thus keep
the cool and dry airmass in place. Deterministic models show an
upper level wave moving northward across Southwest Thursday night
into Friday. There is low confidence in the forecast of this upper
level wave due to significant discrepancies between guidance with
the placement and orientation of this wave. The predominant storm
track will remain over the Bering/Aleutians as North Pacific storm
systems move northeastward along the aforementioned upper high and
into the Bering/Aleutians.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...Storm Warning 411
		 Gale Warning 127 177 178 185
		 Heavy Freezing Spray Warning 119 127 139 160 180 185
FIRE WEATHER...NONE.

&&

SYNOPSIS AND MODEL DISCUSSION...KM
SOUTHCENTRAL ALASKA...JW
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...MV
MARINE/LONG TERM...AH/ED