Gale Warning 619, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
450 PM AKST Fri Nov 27 2020

.ANALYSIS AND UPPER LEVELS...

Quite a busy weather day for our forecast area. Three surface low
pressure systems exist, two of which are weather producers for us
today. First, a surface low just south of Prince William Sound has
been creating impactful weather for Southcentral AK. A deformation
band with this low has produced heavy snow for the Western Susitna
Valley and another band of moisture along coastal Southcentral is
producing heavy snow through Turnagain Pass and snowfall in
Turnagain Arm and Anchorage Bowl. The second low is a strong low
in currently in the Eastern Aleutians, with Hurricane Force wind
gusts wrapping around the backside of the low. A front from this
low is currently entering the Western Gulf of Alaska as well. The
third low is in the Western Bering and not yet impactful. The
three are making for some very interesting satellite shots.

All of this active weather is supported in the upper levels by a
complex longwave trough that encompasses most of our forecast
area. Several upper low centers are spinning within this trough,
three of which are associated with the aforementioned surface lows.
This trough extends all the was from Eastern Siberia to Central
Alaska. Induced shortwave ridging is developing between the low in
the Gulf of Alaska and the low in the Eastern Aleutians, which is
the only bit of ridging that can be seen in our forecast area.

&&

.MODEL DISCUSSION...

On the synoptic scale, models are performing well and in good
agreement. They are capturing the overall weather pattern. When we
focus in on the mesoscale, disagreement and performance issues
emerge with our major models. This is mainly the case for
Southcentral AK. They have had difficulty depicting the current
round of snowfall in Southcentral AK and are having trouble
resolving the next frontal system slated to move into the Gulf of
Alaska tonight. This has made for difficulty in forecasting the
finer details, dropping our confidence level for the next couple
of days, specifically along coastal areas. In the western part of
our forecast area, models are performing better and we have higher
confidence in the forecast.

&&

.AVIATION...

PANC...A heavier band of snow moved through this morning reducing
the airfield to IFR conditions. The heaviest snow has moved
through and MVFR conditions can be expected with light snow
showers into the evening. Winds should stay light and variable.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 through 3:
Tonight through Sunday)...

The amount of snow will vary across from Kenai Peninsula through
Prince William Sound to Anchorage this evening, thanks to
remaining remnants over the Gulf that are still making their way
inland which will bring additional snowfall tonight.

More mixed snow and rain are heading our way as a result of the
next storm from the Bering Sea. The leading edge of the frontal
system from the storm has already reached Kodiak this afternoon,
and this system will race northward toward Kenai Peninsula and
Prince William Sound through Saturday morning. Along the axis of
the frontal boundary, a couple other lows will emerge from it and
may keep snowy conditions near Anchorage Bowl through the weekend.
For now, the models suggest at least two separate microscale lows
with the first one emerging near Kodiak on Saturday morning and
the other over Cook Inlet on Sunday afternoon. It should not come
as a surprise should the areal coverage for snow increases through
Monday. Although strong winds from the frontal boundary will reach
much of Prince William Sound by Saturday morning, but these strong
winds are expected to be short-lived.

Patchy fog was observed around the Anchorage Bowl this afternoon,
and this situation will continue through late tonight. Freezing
spray is also expected in the next couple days mainly over the Cook
Inlet and Kamishak Bay. The combination of moderate to strong
winds and cold temperatures are favorable ingredients for
freezing spray.

&&

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

The cold weather pattern continues across Southwest Alaska this
afternoon, with a few lingering snow showers over interior Bristol
Bay. Cloud cover and the chance for precipitation will increase
this evening for the mainland as a frontal system lifts northward
overnight into Saturday morning. This system has stayed all rain
earlier today for the Alaska Peninsula, which will transition to
snow or a mix of rain and snow as temperatures cool overnight.

The potential for blowing snow across Bristol Bay from Dillingham
to Koliganek is the main focus for this forecast package. As the
front lifts northward, strong winds and gusts are possible, as
well as a few inches of snowfall. Blowing snow is a concern with
these conditions, which could lower visibility to a half mile at
times. Thus, a Winter Weather Advisory for blowing snow has been
issued through Friday morning for these areas.

The Kuskokwim Delta and Valley should stay relatively dry through
Friday, when a chance of snow returns to the Kuskokwim Valley.
Temperatures across the region will continue to fall through the
weekend as northerly flow allows cold air advection to move into
the area.

&&

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

High winds across the central Aleutians will continue through the
evening hours as a storm force low positioned just north of Dutch
Harbor tracks over the Alaska Peninsula and back into the North
Pacific by Saturday morning. A High Wind Warning remains in effect
through this evening for the eastern Aleutians, including
Nikolski, which has already seen warning level gusts of 80 mph.

A second storm force low over the western Bering this afternoon
will continue to weaken overnight as it dives south crossing the
central Aleutians Saturday afternoon and into the North Pacific
through the evening hours. Widespread precipitation will accompany
the two aforementioned systems, diminishing through Sunday
morning.

Another storm force system will move into the forecast area by
Sunday morning, with the associated front tracking over the
western Aleutians. This low will skirt the Aleutians, keeping the
strongest core of winds and widespread precipitation for the
Aleutian Chain as it tracks eastward towards the Alaska Peninsula
for Monday.

&&

.MARINE (Days 3 through 5/Monday through Wednesday)...

Gulf: A weak low lingers in the Northern Gulf through Monday
afternoon before moving onshore and dissipating. On Tuesday, a
series of shortwaves troughs move across the Gulf towards the
North Gulf Coast as a second weakening low approaches Kodiak
Island from the south. Winds will be primarily southeasterly on
Monday, transitioning to southerly by Tuesday afternoon as the
low moves north. Storm force winds may result as the front pushes
the North Gulf Coast, with a barrier jet likely to set up late
Monday night. Winds should begin to dissipate by Tuesday evening.

Bering: A strong North Pacific low pushes towards the western Gulf
over the course of a few days. This results in widespread gales
across the Southern Bering and possible storm force winds along
the central/eastern Aleutian coasts Monday into Tuesday. On
Tuesday the low is positioned further east and lingering gales and
small craft winds will be confined to the Southwest coastal
waters. Additionally, flow will be primarily northerly on Tuesday
with colder air being advected along the coast, thus, freezing
spray is likely, with heavy freezing spray possible along parts of
the immediate coast. High pressure sets up over the Central Bering
Tuesday afternoon.

&&

.LONG TERM FORECAST (Days 4 through 7/Tuesday through Friday)...

A strong front pushes the Southcentral Coast late Monday night.
With this, widespread precipitation is likely, with the heaviest
along Western Prince William Sound and Eastern Kenai. Further
inland, snow is likely through Wednesday morning before becoming a
rain/snow mix in the lower elevation. Significant warm air
follows this front, thus, precipitation along the coast should
start as a snow or rain/snow mix Tuesday morning and transition to
all rain by Tuesday afternoon. Rain will likely linger through
Thursday as a second low pushes the coast from the Southern Gulf.
Precipitation transitions back to snow by Friday with colder air
behind the low.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...
Storm Warning 119 172 174 177 178 411.
Gale Warning 120 125 128 130 132 138 139 140 150 155 160 165 170
173 175 176 180 351 352 413 414 .
Heavy Freezing Spray 180 181.
FIRE WEATHER...NONE.

&&

SYNOPSIS AND MODEL DISCUSSION...BB
SOUTHCENTRAL ALASKA...CB
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...AH
MARINE/LONG TERM...KM