High Wind Warning 20, NWS Anchorage, AK

890 
WWAK71 PAFC 010940
NPWAER

URGENT - WEATHER MESSAGE
National Weather Service Anchorage AK
1240 AM AKST Tue Dec 1 2020

AKZ101-011045-
/O.CAN.PAFC.HW.W.0020.000000T0000Z-201201T1200Z/
Anchorage-
Including the cities of Anchorage, Eagle River, Indian, 
and Eklutna
1240 AM AKST Tue Dec 1 2020

...HIGH WIND WARNING IS CANCELLED...

Gusty winds are diminishing along Turnagain Arm and higher 
elevations, and are no longer gusting to warning levels.

$$

For more information from the National Weather Service visit
http://weather.gov/afc

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
443 PM AKST Mon Nov 30 2020

.ANALYSIS AND UPPER LEVELS...
A vertically stacked storm force low about 500 mb south of the
Aleutians and Alaska Peninsula is embedded within a high amplitude
trough. A strong upper level jet streak extends northward up the
front side of this trough across the western Gulf of Alaska. A
small, but potent short-wave is noted in water vapor imagery
riding this jet northward toward Southcentral Alaska. At the
surface, a triple point low has formed just south of the Alaska
Peninsula and is tracking slowly northward along the Alaska
Peninsula. A frontal system extending eastward from this low into
the Gulf is tracking northward toward Southcentral, producing gale
to storm force winds. Northerly gales are widespread behind the
surface low from the eastern Bering Sea southward to the North
Pacific. The airmass in place out ahead of the low and frontal
system is quite cold. Thus, precipitation spreading northward
across the southern mainland this afternoon is falling as all
snow. However, much warmer air is headed northward across the Gulf
behind the front, which has resulted in a changeover from snow to
rain for Kodiak Island.

Conditions are relatively quiet across the central to western
Bering Sea and Aleutians, with just some snow showers and locally
gusty winds.

&&

.MODEL DISCUSSION...
Models are in good agreement with large scale features through
Tuesday night. There are however some significant forecast
challenges, primarily that of precipitation type over Southcentral
Alaska the next 24 hours. Winds with the strong front and warm air
advection behind the front will lead to a general warm-up in
temperatures and transition in precipitation types from snow to
mixed precipitation or rain. Those areas which see significant
winds will likely warm above freezing, while those areas
protected from the wind will hold in longer with freezing
temperatures at the surface. While overall forecast confidence
is about average, confidence in the details of temperature and
precipitation type is below average.

Model agreement breaks down beginning Wednesday, but do not see
any high impact weather on the horizon once the current storm
winds down.

&&

.AVIATION...
PANC...The forecast for the next 12 hours is quite challenging.
First off, easterly winds will continue to strengthen across the
Kenai and Chugach Mountains this afternoon into early evening as
a front approaches from the Gulf, leading to low level wind shear
at the terminal. Normally this would lead to downslope drying as
well. However, with southerly flow aloft, abundant moisture
transport, and a potent short-wave, there is a good chance for a
brief period of snow between about 03Z and 07Z, which could
temporarily reduce ceiling and vis.

The front will pass through around 06z, with much warmer air
moving in aloft. Downslope flow will weaken, with southerly flow
setting up through most of the column. Some guidance shows a
southeasterly wind making it into the terminal, but with a surface
low still in the Bristol Bay area, think the northerly wind may
hold in at the surface. If so, then the surface temperature will
remain below freezing and there is potential for a period of light
freezing rain Tuesday morning. If the southeast winds were to come
in, then temperatures would warm above freezing. Downslope flow
looks like it will then strengthen again beginning around 18Z,
bringing an end to any precipitation.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 through 2: Today
through Wednesday)...

The well advertised storm system is underway across Southcentral.
Snow and blowing snow was being observed in and around Homer with
these conditions expected to move northward to the Sterling
Highway through the remainder of the afternoon and into this
evening. As a result, a Winter Weather Advisory is in effect
through 9 pm this evening for snow and blowing snow with 1-4
inches of snow accumulation. Conditions will begin to improve
after about 9 pm this evening before the next round of
precipitation moves into the area Tuesday though in the form of
rain as temperatures warm up into the upper 30s and low 40s. The
same frontal system bringing this precipitation currently to the
Kenai Peninsula is expected to move through the Anchorage Bowl
early this evening that is anticipated to lower visibilities for
a short time period and result in up to about a half inch on the
west side of Anchorage to as much as 2 inches across the Anchorage
Hillside especially Glen Alps.

The front continues moving north with a storm force barrier jet
expected through the evening hours with hurricane force gusts to
75 kts near the coast. As the front continues moving northward,
winds will continue to increase in Turnagain Arm and the Anchorage
Hillside with winds peaking around 9 pm this evening. Wind gusts
to 60 mph are expected in Turnagain Arm and on the Anchorage
Hillside. Winds will rapidly diminish after 9 pm once the front
lifts on through, though, winds will remain gusty into Tuesday
with 30-40 mph gusts expected. The Matanuska Valley and the Knik
River Valley wind were already picking up throughout the day as
well with these winds expected to continue through the night. The
Matanuska Valley wind is expected to diminish Tuesday morning but
the Knik River Valley wind is expected to continue throughout the
day Tuesday. As a result of these winds, temperatures across the
Matanuska Valley are expected to rapidly warm Tuesday into the low
40s. Warming temperatures combined with any rain that falls will
create for hazardous travel conditions for the Tuesday morning
commute.

A Winter Storm Warning remains in effect for the northern and
western Susitna Valley this evening through Wednesday afternoon.
Significant snowfall accumulations remain expected for areas north
and west of Talkeetna including the Parks Highway from Chulitna to
Cantwell. One addition to the warning was the risk for freezing
rain across the lower Susitna Valley especially around Willow
where a tenth to two tenths of an inch of ice accumulation are
expected. Cold air is expected to remain at the surface as warm
air moves in aloft through a deep layer creating the atmospheric
profile for freezing rain. The timing on this will be 3 am Tuesday
to 12 pm Tuesday before temperatures finally warm above freezing.
Conditions will remain hazardous though even when temperatures
finally warm up.

Heavy precipitation is expected across Thompson Pass and
Turnagain Pass as well as all the mountain ranges around
Southcentral except for Hatcher Pass where significant snow isnt't
expected as the flow through the atmosphere doesn't favor this
area for very heavy snowfall. Rising snow levels tonight through
Tuesday and into Tuesday night in accordance with heavy
precipitation in the form of snow changing to rain will create the
risk for avalanche conditions through the passes.

Seward is also expecting upwards of 5 inches of precipitation from
this system. As a result, a flood advisory is in effect for this
area through this evening.

Lastly, colder air is expected to move back into Southcentral on
Wednesday as the upper level trough moves on through the region.
There is the potential for a period of snow Wednesday afternoon
into Wednesday night that may result in a few inches of snow
across Anchorage as this lifts through. Stay tuned as we continue
to fine tune this part of the forecast.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 through 2: Monday
afternoon through Wednesday)...

Models are in much better agreement with the surface low today as
they have the surface low tracking near the AKPEN and moving near
King Salmon by this evening. This slight shift has moved the
heaviest snowfall area from just north of Dillingham to east of
Aniak. The heaviest of snow is expected from Sleetmute and areas
east as well as Koliganek and New Stuyahok. Mainly looking at 6 to
8 inches with localized areas of up to 10 inches. Dillingham and
Aniak will see lesser amount of 3 to 5 inches. Winds will also be
gusty out of the north up to 35 to 40 mph so blowing snow will be
an issue especially for Dillingham and areas closer to the water,
this is why Dillingham and others with lesser snow amounts are
included in the winter weather advisory. The main shortwave energy
will track into the interior by Tuesday morning with most of the
heavier snow ending. The parent low near the Bering Strait with a
trough extending south along the west coast of Alaska will support
a surface front across eastern parts of the Bristol Bay region
Tuesday into Wednesday. This front will continue to produce areas
of light snow from near Iliamna to areas east of Sleetmute with
several inches of snow expected through Wednesday. As the trough
slowly pushes east across Southwest Alaska on Wednesday the light
snow will gradually end by Wednesday evening.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 through 2: Monday
afternoon through Wednesday)...

As the low tracks inland tonight a northerly cold air advection
pattern sets up across much of the Bering and Aleutians through
Tuesday with snow showers, and light accumulations in most
populated areas, generally an inch or less. Wednesday high
pressure will dip down from Russia into the northern Bering and
the Pribilof Islands with light winds and less precipitation and
possibly some patchy fog, but did not mention anything in grids as
there is uncertainty due to possible cloud cover. Tuesday
afternoon through Wednesday a complex area of low pressure systems
moves into the western Aleutians and central Aleutians by
Wednesday with areas of light snow or rain/snow mix, but no
significant impacts as the winds will remain at small craft or
less through Wednesday.

&&

.MARINE (Days 3 through 5)...

Gulf of Alaska: The remnants of low pressure linger to start
Thursday, but it is on its way out. The Gulf of Alaska then
quiets for the most part. Cooler air filters back into Gulf, which
will cause gusty winds through gaps and passes along the Western
Gulf, including through Kamishak Bay and the Kennedy Entrance.
Wind direction then becomes generally northerly through the
weekend. The Gulf continues to remain quiet with no major weather
systems in our forecast area during this time.

Bering Sea: The Bering starts out quiet with high pressure in
place. Flow then becomes easterly for the weekend and winds will
increase to small craft advisory level. This is due to a couple
weak lows moving through the North Pacific, just south of the
Aleutians. Confidence is not high with the placement of these lows
due poor model guidance, so wind speeds may need some adjusting.
However, we can anticipate no impactful low pressure systems
moving through the Bering.

&&

.LONG TERM FORECAST (Days 3 through 7)...

We are still expecting a pattern shift to occur late this week,
with the weather noticeably changing starting Thursday. Southerly
flow aloft supporting above average temperatures in Southcentral
AK will push off to the east and allow cooler, more seasonable
temperatures to return. Shortwave ridging looks to develop over
Southwest AK. An upper level low should exist in just south of the
Central Aleutians. As we progress into the weekend, a key
difference emerges from yesterday in that model guidance has back
off the shortwave ridge phasing with high pressure in the Western
U.S. There are still hints of it there, but it's more fuzzy now.
Longwave troughing still looks to return to the Bering Sea.

Since models are less agreement than they are yesterday, not much
can be said for starting to focus in on a forecast solution for
the longterm. This means we can only look out a few days at most
to discern specific weather features. Analyzing the long range
today we do know the weather pattern stays busy. So, we can
expect a pattern shift with continued active weather for our
forecast area. Due to significant model discrepancies, that's
about all we can say for now.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...Winter Storm Warning 145
	     Winter Weather Advisory 121 152 161
		 Flood Advisory 125
MARINE...Storm Warning 119 120 125 130 131 351.
		 Gale Warning 128 129 139 140 141 352 155 165 170 171 172
                      173 174 180 181 414.
	     Heavy Freezing Spray 160 180 181.
FIRE WEATHER...NONE.

&&

SYNOPSIS AND MODEL DISCUSSION...SEB
SOUTHCENTRAL ALASKA...MV
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...RC
MARINE/LONG TERM...BB

SPECIAL WEATHER STATEMENT
National Weather Service ANCHORAGE AK
451 PM AKST Mon Nov 30 2020

AKZ125-010900-
Western Prince William Sound-
Including the cities of Whittier, Seward, Girdwood,
and Moose Pass
451 PM AKST Mon Nov 30 2020

...A Wet, Windy, and Warm Storm is currently impacting the
eastern Kenai Peninsula...

After several cold, snowy storm systems, the next one in line will
bring much warmer temperatures. This will allow for a transition
from snow to rain with snow levels rising to near 2,500 feet by
Tue evening. The weather pattern will also favor heavy amounts of
precipitation. Here are the key take-aways:

Snow and rain: The system will bring a bit of both. It will track
quickly from south to north. Snow is currently falling from Seward
to Portage Valley. However, warm air will push in quickly behind
the front and transition precipitation over to all rain for all
locations near sea level by early Tuesday morning. Precipitation
will be nearly continuous for places like Seward and Whittier
where over 4" are expected by Wednesday morning. For higher
elevations, such as Turnagain Pass, colder air will try to hold
on. However, temperatures will rise to near freezing, so expect
very heavy, wet snow over the mountains. Snow accumulations will
be on the order of 1-2 feet.

Winds: East to southeast winds will steadily increase through
Passage Canal and into the Portage Valley through Monday. Winds
should peak this evening into early Tuesday morning. Gusts to 70
mph are expected.

Travel hazards: This combination of rain, snow, and rain on snow
could result in challenging conditions across the area. Any rain
that falls on snow covered roads could make them especially
slick. Warmer temperatures near the surface can also result in a
thin layer of water on top of snow on the roadways. Please check
in with the DOT for the latest road conditions call 5 1 1 or
visit 511.alaska.gov. Avalanche concerns will also increase with
this pattern. A moderate amount of rain will fall on the new
snowpack over the midslopes with heavy wet snow falling along the
ridgelines. Please visit cnfaic.org for the latest on avalanche
danger.

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE ANCHORAGE AK
831 PM AKST MON NOV 30 2020

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

0824 PM     SNOW             2 NNE STERLING          60.54N 150.76W
11/30/2020  M3.0 INCH        KENAI PENINSULA    AK   TRAINED SPOTTER

&&