Winter Weather Advisory 17, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
444 PM AKST Fri Feb 26 2021

.ANALYSIS AND UPPER LEVELS...

Weak low pressure moving into Southcentral is creating a wintry
mix of weather. Most locations are seeing snow, though freezing
drizzle is present on the Kenai Peninsula and was present in
Anchorage this morning. So far, it has remained cold enough in
Anchorage to remain snow since then. The center of this low
affecting Southcentral is still located back in Southwest AK,
also providing a wintry mix of precipitation there. Temperatures
are warm enough in Southwest AK for more of a rain/snow mix there.

All of this is being supported by an upper level trough and 500MB
closed low over the Bering Sea. It is embedded in a zonal pattern
moving across our forecast area. However, this trough is beginning
to dig south and the pattern is becoming more amplified.

&&

.MODEL DISCUSSION...

Synoptically models are in good agreement to start the short term.
They do begin to diverge in placement of features over the
weekend, notably with an upper level low moving along the north
gulf coast. The surface low associated with this seems to be
handled better, but some minor disagreement exists there as well.
On a more local scale, models are having difficulty handling light
precipitation moving into Southcentral AK. So, adjustments to the
forecast have been necessary today.

&&

.AVIATION...
PANC...MVFR conditions will be present through the TAF period.
Low pressure in the area will make for intermittent periods of
snow, reducing visibility to MVFR at times with low-level cloud
cover remaining in place. Additionally, turnagain arm winds are
expected to develop this evening. There remain some questions as
to whether or not they will work their way into the airfield. For
now, it looks like they will stay aloft, so low-level wind shear
was added into the TAF.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 through 3: Today
through Monday afternoon)...

Active weather will continue across Southcentral through mid-
week. A weak warm front combined with an upper ridge is tracking
across the region. The freezing line is currently located just
north of Anchor Point. It is difficult to determine how far north
this will get. Kenai forecast soundings show a saturated
isothermal layer between the surface and approximately 900 mb
before cooling aloft. This supports the continued potential for
freezing drizzle and as such a Winter Weather Advisory has been
issued through Saturday afternoon. While much of the precipitation
is expected to fall as all snow, a slight temperature deviation
at or slightly above the surface could lead to more freezing
drizzle or even brief freezing rain. In any case, travel between
the Seward/Sterling Highway junction and Clam Gulch may be
difficult at times.

Farther north, temperatures will peak near freezing in Anchorage
and the Matanuska Valley. Light snow will persist through Saturday
with the heaviest occurring overnight tonight into early Saturday
morning. Gusty southwesterly winds are likely near Turnagain Arm
and the Anchorage Hillside. Depending on how far north the front
gets, winds may briefly turn into town, however as of now it is
expected that they remain confined to the coast. Higher snow
totals are likely across the Susitna Valley and thus the Winter
Weather Advisory remains in effect there through Saturday evening.
The northern Copper River Basin will also see similar
accumulations, mainly in the Paxson area and the Advisory remains
there as well through the same time period.

Snow showers will continue over much of the region through Sunday,
though localized downsloping may occur. Several additional inches
are possible in the Copper River Basin. A low tracking into the
Gulf will increase northwesterly outflow winds though the day,
particularly in the Whittier area. This will lead to blowing snow
continuing after the snow has ended. Travel through Isabel Pass
may be difficult. Much cooler temperatures will result as well.
An upper ridge will lead to a brief lull on Monday morning before
a similar system enters the Gulf by the afternoon.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 through 3: Friday
Afternoon through Monday)...

An upper level shortwave over the eastern Bering Sea is supporting
a low and frontal system moving onshore tonight this will bring
snow to the Kuskokwim Delta with 2 to 4 inches of snowfall. While
farther south over Bristol Bay where temperatures are above
freezing a mix of rain and snow will prevail when little if any
snow accumulations. This front will move towards the interior by
Saturday morning rain and snow ending, some patchy fog is possible
across the Bristol Bay area from Dillingham to King Salmon
Saturday morning. As the cold front pushes south and east on
Saturday cold air and northerly winds will move across the area
with temperatures dropping from north to south through the day.
Cold and dry for Sunday as northerly flow dominates.

Sunday night and Monday a strong frontal system crossing the
Bering Sea will bring increasing south to southeast flow with
warmer air pushing temperatures near freezing along coastal areas.
This will result in snow across the region with several inches
expected beginning Sunday night and continuing through Monday.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 through 3: Friday
Afternoon through Monday)...

A shortwave trough and frontal system will move across the eastern
Bering tonight and move inland. Behind the cold front, cold air
advection will bring snow showers to the AKPEN and eastern
Aleutians Saturday through Sunday morning. This cold air will also
produce gusty winds across the AKPEN and eastern Aleutians with
Gales and pockets of storm force winds south of the AKPEN Saturday
night and Sunday.

Farther west a low continues to spin north of Shemya. This will
produce some high end small crafts across the northwest Bering
this evening with heavy freezing spray near and west of St Matthew
Island.

Saturday evening a strong front will move across the western
Aleutians into the Bering with high end storm force winds and
hurricane force gusts. The parent low to this front will bring
hurricane force winds across the western Aleutians Sunday through
Sunday night these will spread towards Adak and the central
Aleutians Monday with storm force winds and hurricane force
gusts.

This strong front on Sunday and Monday will create hazardous
heavy freezing spray for a good portion of northern and eastern
Bering Sea extending as far south as the Pribilofs Island and
southeast towards Bristol Bay and south of the AKPEN.

&&

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

Bering: A well developed low and front tracks across the Bering
into Southwest Alaska for Tue. Model confidence is good, but
decreases near the end of the period. Widespread storm force winds
and waves with areas of hurricane force gusts with the wind
wrapped low and front as it moves east, diminishing from the west
Tue. Widespread gale force winds take over through Wed. Waves to
47 feet over the Aleutians and Bering, subsiding in the Eastern
Bering by Wed.

Gulf of Alaska: A low and front move across the Gulf for Tue. A
second front is hot on the heels through Wed. Confidence is good
through the forecast. Widespread high end gale force winds and
waves move across the Gulf for Mon and Tue. Gusty outflow winds
spread into the Gulf from Kachemak Bay and the Barren Islands,
down the lower Shelikof Strait and along coastal Alaska Peninsula
for Wed. Waves build to 22 feet move across the Gulf through Wed.

&&

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

The long term forecast period overall looks quieter as an Arctic
trough moves through much of the Mainland for next week. Overall,
a cold pattern is expected for this time frame as rounds of
Siberian/Arctic air move across the northern Bering and Bering
Strait across the Alaska Mainland. The pattern is expected to be
more progressive as well meaning that this cold air will be pushed
through the gaps and passes of the Alaska/Aleutian Range and down
the Alaska Peninsula to the eastern Aleutians. This doesn't look
to be the typical setup for the Southcentral gaps and passes to
really blow strongly but winds will still be on the uptick for
next week. The coldest days as of now appear to be Tuesday and
Wednesday when temperatures will be well below normal across
Southwest and Southcentral Alaska. A weak upper level ridge will
nudge its way into Southwest Alaska Thursday which may bring snow
to the Southwest areas of Alaska. However, another round of cold,
Arctic/Siberian air is lurking behind this ridge that will push
this ridge off to the south and not make much progress into
Southcentral Thursday and Friday. At most, some light snow may
occur for Kodiak and the eastern Kenai Peninsula late week though
temperatures will still remain below normal.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...Winter Weather Advisory 121 141 145.
		 High Wind Watch 191.
MARINE...Storm Warning 130 131 138 176-178 411 413.
		 Gale Warning 120 129 132 137 150 155 160 165 173-175
				      351 352 412.
		 Heavy Freezing Spray Warning 130 131 139 150 160 165
	 								  180 185 411 412 414.
FIRE WEATHER...NONE.

&&

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