Winter Storm Warning 5, NWS Anchorage, AK

865 
WWAK41 PAFC 280245
WSWAER

URGENT - WINTER WEATHER MESSAGE
National Weather Service Anchorage AK
545 PM AKST Fri Nov 27 2020

AKZ145-280345-
/O.EXP.PAFC.WS.W.0005.000000T0000Z-201128T0300Z/
Susitna Valley-
Including the cities of Talkeetna, Willow, and Cantwell
545 PM AKST Fri Nov 27 2020

...WINTER STORM WARNING WILL EXPIRE AT 6 PM AKST THIS EVENING...

Some light snow continues, but will gradually taper off later 
this evening.


$$

AKZ121-280345-
/O.EXP.PAFC.WW.Y.0035.000000T0000Z-201128T0300Z/
Western Kenai Peninsula-
Including the cities of Kenai, Soldotna, Homer, 
and Cooper Landing
545 PM AKST Fri Nov 27 2020

...WINTER WEATHER ADVISORY WILL EXPIRE AT 6 PM AKST THIS
EVENING...

Snow has mostly ended across the area, with only a few isolated 
snow showers expected for the remainder of this evening. 

$$

http://www.weather.gov/afc

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

.ANALYSIS AND UPPER LEVELS...

A large trough extends from eastern eastern Russia to the AKPEN
with a ridge over the Alcan border. Multiple strong shortwaves
extend from the eastern Bering to the central Gulf just north of
the primary jet axis. Active weather is present over the western
Bering, Aleutian Chain and Southcentral while Southwest is mostly
calm with low stratus.

Over the Gulf, a compact low can be seen on satellite moving
north towards the Prince William Sound. The low level circulation
has taken on a slight negative tilt with the low center expanding
in area as well. Radar returns over the Middleton island show
convective showers to the north of the low center. The Kenai radar
shows a narrow deformation band extending from Kenai city to
Skwentna. This band is the primary focus for the eastern domain
forecast in whether or not it will remain over the western Kenai
Peninsula or drift east over Anchorage.

Out west two compact lows can be seen on satellite. The stronger
of the two is currently over Nikolski and brought storm force
winds to the south of Adak early this morning. Surface
observations at Adak measured peak winds of 43 kts. This storm is
about 50 miles south of where it was forecast, resulting in lower
windsover the central Aleutians. The second storm to the north of
Shemya has also been measuring storm force winds at buoy 70.

&&

.MODEL DISCUSSION...

Models changed drastically in the afternoon and evening runs in
regards to the track of the Gulf low. The evening package models
indicated a deformation band setting up from Anchorage north to
Willow which aligned with both the GFS and NAM 00Z models runs.
Overnight the deformation band has moved slightly to the west and
now extends north south from Skwentna to Kenai City which aligns
with the 06Z NAM and GFS solutions. This deformation band formed
with system that moved over the Cook Inlet Thursday afternoon. It
is difficult to discern whether or not the band has been
influenced by the low in the Gulf at the time the forecast
issuance, however at this time there is no indication that the
band will move back to the east to bring heavy snow from Anchorage
north to Willow.

&&

.AVIATION...
PANC...Based on current radar observations the band of heavy
snow which had the potential to cause periods of heavy snow over
the area, has set up west of the airport. It is currently expected
the band will mostly remain west of the airport for the day.
However, potential eastward jogs may temporarily deteriorate
conditions. Thus, have significantly improved the conditions over
the airport today from previous forecasts. There still remains
significant uncertainty, so left a period of MVFR snow in for
later this morning, when the band is most likely to make its
closes approach. If trends continue keeping the band west of the
airport, the morning TAF will need to be improved to VFR for the
entirety of the day, with only occasional snow showers that make
it over the mountains being the only threat for snow. Expect
further adjustments through the morning as certainty improves.

&&

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

An incredibly complex and dynamic weather scenario is unfolding
across Southcentral this morning. An area of low pressure moved up
Cook Inlet yesterday evening, with a Gulf low now having taken
over as the main low. The importance of the first low was to set
up a deformation band of snow over the Kenai Peninsula, extending
into the western Susitna Valley. A number of the evening model
runs indicated the band of snow would move east into Anchorage,
the western Matanuska Valley, and along the Parks Highway. This
has not happened. Instead, the band of snow remains parked in much
the same area as it formed. The second Gulf low at this point is
certainly feeding moisture into the snow band, but has not moved
it much. If anything, the band has been slowly crawling westward
with time. The latest NAM run shows the band perhaps drifting a
back to the east a bit later this morning into the interior Kenai
Peninsula, but keep all of the Anchorage Bowl and the Matanuska
Valley dry. Any potential snow could occur if the influx of Gulf
moisture widens the band such that south and west Anchorage may
briefly get a bit of snow. Otherwise, any snow showers will be the
stronger survivors of the downsloping largely keeping Anchorage
and the Mat Valley dry today. Thus, have cancelled the Winter
Weather Advisories for Anchorage and the Mat Valley.

Meanwhile, for the Kenai Peninsula and the Susitna Valley, the
steady snow associated with the band could result in large
snowfall totals for areas that stay in the band longest, assuming
it doesn't move all that much. Winter Weather Advisories are in
effect for these zones, but would not be surprised if localized
totals above a foot are realized, especially in the western
Susitna Valley near Skwentna, which has the benefit of upslope
enhancing the snowfall rates. Steady snow will continue all day
through the Kenai Mountains, with Turnagain Pass potentially
approaching 2 feet of new snow by the time the steadiest
precipitation is over. For lower elevation locations, just enough
warm air is allowing rain to mix in with the snow in Whittier and
Portage. Seward may mix with rain at times as well today.
Hazardous driving conditions from steady snow are expected all
along the Seward Highway from Turnagain Pass south and along the
Sterling Highway from Kenai-Soldotna east.

The Gulf low will lift into Prince William Sound and the coastal
mountains this afternoon and dissipate. This will also cause the
inland snow band to rapidly fall apart and dissipate. The break
in the weather will be very short, if there's one at all along the
coast. A front associated with a strong low will move into Kodiak
Island late this afternoon into this evening, then rapidly shift
northward to the north Gulf Coast tonight. Winds with the barrier
jet will increase into storm force late tonight into Saturday
morning as the front approaches. The front will keep steady snow
ongoing along the coastal mountains through the day on Saturday.
The front itself will dissipate during the day, but the onshore
flow behind the low will keep upslope precipitation ongoing. There
remains some uncertainty, but the parent low center currently is
expected to move into Prince William Sound late Saturday night
into Sunday morning. Thus, expect the mountain snow along the
coast to continue more-or-less steadily through Sunday morning.
Some of that moisture could make it inland, especially into the
southern Copper River Basin Saturday night, but with the
incredible spread in the models with the present system, it can't
be ruled out that the Cook Inlet region has at least some chance
of snow with that track as well.

&&

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

A fairly benign but cold weather pattern is instore for Southwest
Alaska over the next 3 days. A storm system is moving east-
northeastward across the eastern Aleutians and along the AKPEN,
placing the Kuskokwim Delta and Bristol Bay to the northwest of
the low center. This will promote strong cold air advection as
east- northeasterly winds will bring in continental polar air from
the Alaskan interior to the area. Observations and radar show
snow falling across Bristol Bay as the outer snowbands are
currently moving across that area. Precipitation type is not an
issue for this system as temperatures will remain cold enough to
support snow for the entirety of the event. The next 2 days will
be fairly dry with a cooling temperature trend as brisk
northeasterly offshore flow continues.

&&

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

A storm system is currently moving east-northeastward along the
central and eastern Aleutians today. Widespread storm force winds
are expected across the area. The High Wind Warning was cancelled
for the central Aleutians as observations and ASCAT data showed
winds below warning level criteria during the peak of the event.
Winds will gradually decrease across the central Aleutians today
in the wake of this storm system. A second area of low pressure in
the western Bering will gradually weaken today, though it will
produce gale force winds in the western Bering/Aleutians. A third
low pressure system will move into the western Aleutians Saturday
evening and continue eastward through Monday afternoon. There is
confidence the center of this low will remain well to the south,
however the northern edge of this system will bring widespread
gale force winds and areas of storm force winds Saturday night
through Monday afternoon. The largest seas expected with this
storm will be on the Pacific side of the Aleutians and will reach
20-30ft Monday morning through Tuesday morning. These seas will
remain long in period.

&&

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

Gulf: The active pattern continues with high winds and waves
following back to back storms into the Gulf. A gale force low
will move into the Gulf Saturday afternoon, expected to dissipate
throughout the day on Sunday. Monday morning, a front associated
with a low south of the Chain will enter the western Gulf. This
system could bring storm force winds as it propagates towards the
northern Gulf Coast with a barrier jet looking to set up Monday
evening. After this, strong southerly flow will overtake the Gulf
Tuesday morning, expected to dissipate throughout the day.

Bering: A large and strong area of low pressure looks to skirt the
Chain beginning on Sunday morning bringing with it the potential
for storm force winds and waves. Expect high winds and waves into
the central Bering between Sunday morning and Tuesday afternoon.
Tuesday evening, most of the high winds and waves look to remain
confined to the eastern Aleutians and Bering which should begin
to dissipate through Wednesday. After this, there looks to be a
short break in the active pattern through Thursday with calm winds
and seas.

&&

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

The active weather pattern continues throughout the long term.
Precipitation will continue for the northern Gulf Coast with snow
for the higher elevations on Monday, as an area of low pressure
continues to weaken as it moves further inland. Temperatures look
to remain warm with this feature, with rain expected for the lower
elevations and snow for the highest elevations. Right behind this
is a front associated with a low in the North Pacific, bringing
another round of precipitation to Kodiak Island and then to the
coastal areas Monday afternoon, along with an increase in winds.
Expect precipitation to make its way inland Monday evening with
this front. Temperatures aloft look to remain relatively warm,
with rainfall looking to be the dominant precipitation type with
this system. We look to dry out a bit after this, with
precipitation mostly remaining across the coastal locations and
higher elevations Wednesday. This looks to continue through
Thursday, with an increase in precipitation expected, as another
low is anticipated to move from the southern Gulf into Prince
William Sound. This could switch rain, from the previous low, to
snow as warm air is replaced by cold air.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...Hurricane Force Wind Warning 174.
Storm Warning 119 155 172 173 175 176 177 411.
Gale Warning 120 125 130 131 138 139 150 160 165 170 171 178 180 351 352
413 414.
Heavy Freezing Spray Warning 180 181.
FIRE WEATHER...NONE.

&&

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