Heavy Freezing Spray Warning 104, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
546 AM AKST Fri Mar 5 2021

.ANALYSIS AND UPPER LEVELS...

A front moving eastward from Southwest to Southcentral Alaska
continues to be the main weather maker across the region this
morning. This system brought blizzard conditions and advisory
level snowfall to the Southwest mainland yesterday afternoon, with
conditions improving through the morning hours today as the front
weakens. Quiet conditions across Southcentral are coming to an end
this morning as the aforementioned front approaches.  A triple
point low has developed near Kodiak Island overnight with a long
fetch of moisture being pulled in from about 45N visible on
infrared imagery. Farther west, strong winds and snowfall brought
reduced visibility to the Pribilofs as a quick moving system
moved over the Bering, which are slowly improving this morning.

&&

.MODEL DISCUSSION...

Models are still doing well in the short term with synoptic
features. However, models are still having trouble with the small
scale features as the front weakens and moves over Southcentral
today. The biggest uncertainty is the chance for snowfall across
the Anchorage Bowl and Kenai Peninsula into Saturday morning.

&&

.AVIATION...

PANC...VFR conditions and light winds will persist. Chances for
snowfall return tonight, but should not significantly worsen
conditions.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 and 2: Today
through Saturday Night)...

A front and associated low have moved into Southcentral this
morning. The forecast remains largely unchanged for Kodiak Island.
Snow has begun across all of Kodiak and Afognak Islands, and will
persist through at least midday for most areas, though the falling
snow may end by late morning across the southern portions of the
island. Temperatures are right around freezing, and the snow and
cloud cover should hold them right around there through the end of
significant precipitation around midday. Strong northwesterly
winds behind the front will usher in a renewed colder air mass,
which will result in widespread freezing spray across the marine
areas around Kodiak Island tonight through Saturday morning. These
winds may pick up some of the snow from this morning and blow it
around, resulting in localized reductions in visibility,
especially around Akhiok. See the Winter Weather Advisory for more
details.

Agreement in the guidance farther north regarding snow for the
mainland has improved significantly overnight, likely due to the
development of the initial band, which is evident over the
Sterling and Soldotna area as of this writing, which extends
north into the Susitna Valley. Therefore, confidence in a
widespread 2 to 5 inches of accumulation across the Western Kenai
Peninsula has also greatly increased. The uncertainty continues to
reside with any localized atmospheric disturbances that may
impact the band, which are notoriously difficult to forecast. As a
result, the confidence on which areas are closer to 5 inches of
accumulation remains fairly low. However, from Homer through
Cooper Landing, at least 2 inches of accumulation by Saturday
morning for most areas is expected. See the Special Weather
Statement for more details.

Elsewhere across Southcentral, there remains some uncertainty with
the band's impact across the Susitna Valley. In general, with a
slow westward drift expected with the band, most of the Parks
Highway should see only a light accumulation. The heavier snow
will set up west of the Parks.

Confidence is also much higher for the forecast for Anchorage and
the Valley. Essentially, the area now looks to escape much, if not
all snow with this band, as it all stays west of the area.
Therefore, chances of snow and accumulations have been reduced
significantly. With some shower activity developing on the eastern
side of the band, a stray flurry or snow shower cannot be ruled
out today. When the cold air moves in late Friday night through
Saturday morning, the northwesterly flow may allow for some
upslope to produce up to an inch of snow along the Hillside, but
that is also fairly uncertain.

Skies will clear for most areas Saturday night. The gap winds
will be going with near gale force winds expected through Seward
and Whittier, and gale force gusts likely through Thompson Pass
and the Copper River Delta. Elsewhere, expect another cold night
Saturday night.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 through 2)...

An occluded front extends from Yukon Delta through AKPEN this
morning, where steady light snow continued to fall east of
Nushagak Hills, including Sleetmute and Iliamna. Cold air
advection will remain over the region, with the next wave of much
colder air advection moving across Nunivak Island and Kuskokwim
Bay tonight into Saturday. A warm front moving in from the western
Bering will drive warmer temperatures around Kuskokwim Bay and
Kuskokwim Delta by Saturday morning. However, strong winds aloft
combined with CAA will produce snow accumulation up to 3 inches
for Kuskokwim Delta on Saturday.

Unsettled but generally benign weather will continue across
Southwest Alaska as brisk onshore flow continues over the next
couple days. This will bring snow showers at times, though no
significant snow is expected. We are also monitoring the potential
for coastal flooding along coastal Bristol Bay and the northern
AKPEN on Friday afternoon as strong westerly winds and large long
period westerly swell move into Bristol Bay. As of now the chance
only looks to be marginal at best, though we will continue to
monitor and keep you well advised.

&&

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

Strong gales embedded within the westerly flow trailing a surface
trough east of Pribilof Islands will continue to impact both Saint
Paul and Saint George this morning until winds diminish in the
afternoon. For this reason, the Winter Weather Advisory for
Pribilof Islands was extended until 10 AM AKST this morning to
reflect this situation. Overnight observations from Saint Paul
indicated a maximum sustained wind of 43 knots with high gusts up
to 56 knots. Steady moderate to heavy snow and blowing snow
conditions continued into early this morning, and these conditions
will persist for the next several hours until mid- morning today.

Gales with higher gusts will move across the Bering and around the
Aleutians coast for the next day or two. The presence of heavy
freezing spray along the Kuskokwim Delta and Etolin Strait today
and around Saint Matthew waters today and Saturday should be
closely monitored.

The next frontal system from a low east of Kamchatka will elevate
swells and winds as the front moves east and across the Bering
Sea and the Aleutians through the weekend. The P-type will be
rain/snow mix through Saturday morning, followed by pockets of
rain from the North Pacific in response to a warm front upstream
Saturday afternoon. Overall, the forecast period will remain a
bit active in the next couple days.

&&

.MARINE (Days 3 through 5: Sunday through Tuesday)...

Bering Sea: A Northern Bering low tracks into Northwest Alaska
through Tue. Forecast confidence is good. Widespread small craft
winds and waves with some areas of gale force winds move into the
Northern Bering Sun, diminishing Tue. Seas to 19 feet over the
Central Bering and Pacific side of the Aleutians subsides by Tue.
A new low and front moves across the Central Aleutians and Bering
through Tue. Seas 14 feet Tue.

Gulf of Alaska: A low exits the Gulf late Sun. Forecast
confidence is good. Widespread small craft winds and waves
diminish over the Gulf late Sun. Wave heights 12 feet subsiding. A
new low and front enter the Western Gulf Mon, moving to the
Central Gulf Tue. Widespread small craft winds spread across the
Gulf with the front. Areas of gale force winds with the low center
over the Barren Islands, Southern parts of Shelikof Strait and
around Sitkinak Tue. Waves building to 14 feet for late Mon into
Tue.

&&

.LONG TERM FORECAST (Days 4 through 7: Monday through Thursday)...

An Arctic/Siberian upper level low that has been in place across
eastern Russia for quite some time now will continue to remain in
place through the forecast period. However, the one difference is
that this upper level low will finally begin moving northward over
the Arctic Ocean by the Wednesday night into Thursday timeframe.
An upper level ridge in place across much of the Alaska Mainland
early on in the forecast period will move off to the east and be
replaced with another blast of cold air. Although, this time the
air mass doesn't look to be as cold as the current one we are in
but still cold nonetheless. Overall, expect below normal
temperatures for the forecast period with Tuesday being the
closest to near normal temperatures before dropping back down yet
again. Precipitation-wise, a storm system is currently anticipated
to track from the Bering across Southwest Alaska and then through
Southcentral Monday through Tuesday time period with snow chances.
Another storm system is possible behind this one towards the end
of the forecast period bringing the potential for more unsettled
weather.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...Winter Weather Advisory 152 171 195.
MARINE...Gales 130-32 150 155 160 165 170-81 185.
         Heavy Freezing Spray 180 185.
FIRE WEATHER...NONE.

&&

SYNOPSIS AND MODEL DISCUSSION...ALH
SOUTHCENTRAL ALASKA...JPW
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...CMB
MARINE/LONG TERM...MK/MV

SPECIAL WEATHER STATEMENT
National Weather Service ANCHORAGE AK
1001 AM AKST Fri Mar 5 2021

AKZ181-060300-
Alaska Peninsula-
Including the cities of Cold Bay and Sand Point
1001 AM AKST Fri Mar 5 2021

...TRACE ASHFALL POSSIBLE IN THE VICINITY OF VENIAMINOF...

The Alaska Volcano Observatory has detected some activity and low
level ash emission in webcam and satellite data from the
Veniaminof Volcano located north of Perryville. Any ashfall is
expected to be of trace amounts.

Surface winds are expected to briefly be out of the southwest this
morning. Surface winds are then expected to shift northwesterly.
Any potential ashfall would be to the south or southeast of the
volcano.