Heavy Freezing Spray Warning 102, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
500 AM AKST Wed Mar 3 2021

.ANALYSIS AND UPPER LEVELS...

Lingering showers have diminished across the North Gulf Coast this
morning as a mature complex low in the Gulf exits southward. Low
stratus and fog over Cook Inlet has moved over Anchorage early
this morning. Along the coastal locations, the northerly outflow
pattern continues out of the usual gap areas across Southcentral.
Farther west, conditions have improved from blizzard criteria
across the Southwest mainland, Aleutians, and Pribilofs overnight.
However, strong winds and lingering snowfall continue early this
morning. Brief upper level ridging is set up behind this system
across the central Bering and Aleutians, with the next storm force
front just west of Shemya ready to enter the western Bering.

&&

.MODEL DISCUSSION...

Models remain in good agreement with the synoptic pattern over
the Bering Sea over the next few day. By Friday, models start to
diverge with the development of a triple point low near Kodiak
Island. There is still some uncertainty in the track and strength
of the low position and whether this will bring snowfall or
downsloping to Southcentral by the end of the week.

&&

.AVIATION...

PANC...Freezing fog over Cook Inlet has drifted into the terminal
this morning. Conditions should improve by this afternoon with
light northerly winds and VFR conditions expected.

&&

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

The weather begins to turn a bit more active by the tail end of
the forecast period Thursday night into Friday. Until then, gap
winds, freezing spray in many of the marine areas, and freezing
fog around Cook Inlet will be the primary hazards.

Freezing fog has developed around the Anchorage area, down
Turnagain Arm, and along the western foothills of the Kenai
Mountains this morning. The dissipation of at least some of the
high cloud cover that started out the night last night is likely
at least part of the cause of the fog, along with lingering
moisture. With the strengthening March sun, the fog should
dissipate, or at least lift by around midday today in most areas.
However, the fog is likely to redevelop again tonight with very
little change in the large scale weather pattern expected between
now and tonight.

With the renewed shot of colder air, freezing spray (with
localized areas of heavy freezing spray) will be an issue both
today as the winds increase through the gaps through Thursday
morning, and then again after the next front moves through on
Friday through Friday night. The freezing spray concern will be
felt even around Kodiak Island. For most of the rest of
Southcentral, it should simply mean continued below normal
temperatures through the forecast period.

The gap winds will keep conditions windy through Resurrection Bay
and Seward, the Whittier area, Thompson Pass, and the Copper River
Delta through Thursday morning. Gusts to 60 mph are possible
through Thompson Pass and the Copper River Delta, with gusts to 40
mph possible for Whittier and the Seward area.

The next bout of snow is expected from Thursday night through
Saturday morning for portions of the area. Since this moisture
will be largely devoid of warm air, as it will be a cold air mass
replacing a warmer, but still below freezing air mass, most areas,
even along the coast should see at least mostly snow. The snow
will begin around midnight Thursday night as a front eventually
succumbs to a low developing along it. The low center will track
just south of Kodiak Island by Friday morning, but Gulf moisture
with temperatures right around freezing could make for several
inches of accumulation across Kodiak Island. The snow will quickly
spread north along the coastal mountains Friday morning, but
Anchorage, the Valley, and the western Kenai will start off
largely downsloped, with little in the way of any precipitation
expected. That could change come Friday evening into Friday night
with the approach of an upper level wave and the Gulf low moving
away effectively ending the downsloping. While we are generally
looking at a 1 to 4 inch snowfall event as of now, that remains a
highly uncertain forecast. Stay tuned for updates.

&&

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

The radars at Bethel (PABC) and King Salmon (PAKC) have been
active overnight and early this morning. Northerly and
northwesterly winds have been strong enough to causing drifting
and blowing snow. The tight pressure gradient over southwest
Alaska will continue into the afternoon, then it will slacken and
there will be a lull. Thursday morning the winds will shift as a
new front moves into the eastern Bering. Another batch of snow is
forecast for Southwest Alaska on Thursday. The potential exception
will be the Alaska Peninsula which could see a rain snow mix.

&&

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

In the wake of the recent frontal passage, northerly flow has set
up over the eastern Bering. Meanwhile, a new front is pushing into
the western Bering complete with a "baroclinic leaf" on satellite
imagery. Early this morning, the ASCAT (Advanced Scatterometer)
data detected gale force winds with the enhanced northerly flow
over the eastern Bering and the new front impacting the western
Aleutians. There is a a weak transient ridge over the Central
Aleutians. However, the pattern is so progressive the new front
will be over the eastern Aleutians and moving into the western
Alaskan mainland Thursday afternoon. Expect more unsettled weather
for the Bering and the Aleutians the next 48 hrs.

&&

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

Bering Sea: A low and trailing front approaching the Alaska
Peninsula from the west will bring widespread westerly gales with
an area of storm force winds and 30 feet seas moving with the
low, or north of the Eastern Aleutians on Fri morning. Winds
decrease to gales over the Eastern Bering by Sat with seas
decreasing to 20 feet. Another strong front moves north across the
Western Bering/Aleutians late Fri into Sat. High end westerly
gale force to possibly storm force winds and seas building to 25
feet over the Western Bering are expected for Sat. Some model
uncertainty persists, but overall confidence is good. A low
approaches the Central Aleutians from the North Pacific early Sun
with southerly gales spreading into the central Bering with seas
remaining in the mid-20s through Sun. Up to storm force winds are
again possible for parts of the central Bering with this next
system on Sun, but confidence for these higher winds is lower by
this point in the forecast.

Gulf of Alaska: A low and front trailing to the south of Kodiak
Island move into the western Gulf Fri with northwesterly gales
moving in over the western bering just behind low and front. Waves
build to 10 to 15 feet in the western Gulf on Fri and up to 20
feet in the southern Gulf by early Sat. Confidence for this
portion of the forecast is good, but uncertainty for the low track
increases as it drifts towards the central/northern Gulf on Sat.
There is better confidence for a region of at least northwesterly
gales to continue southwest of the low near the southeastern Gulf,
but the region of highest winds will depend on the uncertain low
track. By Sun, confidence increases for the low to exit into the
North Pacific with northerly winds decreasing to small crafts or
lower and seas subsiding to 10 feet by Sun evening.

&&

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

The models are in surprisingly good agreement at the start of this
forecast period, with only moderate agreement through the
weekend. The active pattern is expected to continue.

Models keep a strong Arctic/Siberian upper level low rotating
around northeast Russia with an attendant trough stretching
southeastward across western Alaska and the eastern Aleutians at
the start of the period. A shortwave moving along the trough
extending from the aforementioned upper low will help force a
lower level circulation which may develop over the Alaskan
Peninsula and track into the northern Gulf. While details are very
much uncertain with this and even farther out, there could be
another trough moving across the Aleutians and Bering at the end
of the forecast period.

Overall, expect milder temperatures for this time period with
readings still slightly below normal but closer to the normal
values of where they typically are this time of the year which is
near 32 degrees F for Anchorage. This pattern could potentially
mean a snowier regime for Southcentral and in particular across
the Anchorage Bowl. However, many factors have to come together
for Anchorage to get the snow, though, the storm track looks
favorable with model guidance mostly bringing lows near and into
Prince William Sound with details of each uncertain.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...Winter Weather Advisory 181.
MARINE...Storm Warning 177 178 185 411
         Gale Warning 130 131 138 150 155 165 171-76
                      179 180 181 412-14
         Heavy Freezing Spray 121 130 160 165 179 180
                      185 411 412 414
FIRE WEATHER...NONE.

&&

SYNOPSIS AND MODEL DISCUSSION...ALH
SOUTHCENTRAL ALASKA...JPW
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...PJS
MARINE/LONG TERM...AS/NR