Winter Weather Advisory 34, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
505 AM AKDT Fri Apr 2 2021

.ANALYSIS AND UPPER LEVELS...

Broad high pressure overtakes much of Southern Alaska while lower
pressure exists over the Central and Northern portions of the
State. An almost stationary front sets up between the two
features, transporting a decent amount of moisture and warmer air
across the Bering into Southwest Alaska. Most of the associated
precipitation will get hung up on the western side of the Alaska
range for a time before spilling over into parts of the Mat-Su
Valleys Saturday afternoon. An upper level longwave trough pushes
into the western Bering late Saturday morning and pushes east
through the weekend. This trough will eventually flatten the ridge
as it moves across the Southern Mainland. Multiple shortwaves
ahead of the trough will likely result in periods of widespread
light precipitation across Southern Alaska Saturday and Sunday.

&&

.MODEL DISCUSSION...

Models are in good overall synoptic agreement for the first couple
days. Discrepancies begin late Saturday into Sunday with the NAM
digging the trough further south than the other models. Models are
picking up on a couple of weak surface lows look to form in the
Gulf on Saturday. There is some differences with timing, but
otherwise look fair overall.

&&

.AVIATION...
PANC...VFR conditions and light winds will persist.

&&

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

Weather remains generally quiet for Southcentral AK. Weak low
pressure in the Gulf, with high pressure and cooler temperatures
over mainland AK to continue gusty winds through gaps and passes
along the coast. Winds remain strong through Kamishak Bay and
Shelikof Strait as well, continuing freezing spray there. We
expect cold air and windy conditions to stay stronger a little
longer than initially expected along all areas of the coast, so
this was reflected in the forecast tonight. However, winds should
decrease enough this morning that the heavy freezing spray threat
will subside.

Headed into the weekend, another upslope precipitation event is
setting up for the Northern Susitna Valley. Flow will begin to
shift moving up the valley tonight, starting to bring precip into
the upper reaches of the valley and Broad Pass. The brunt of the
upslope flow will begin late tomorrow and last into Sunday. This
event will not be dynamically driven (no weather system causing
it). It will simply be wind direction headed up valley. The
Talkeetnas can also expect snow. A trough pushing through
Southcentral Monday should end the event. Meanwhile, weather will
be quiet for the rest of Southcentral, with cooler temperatures
remaining in place. So, winter continues its hold on Alaska.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 and 2: Friday and
Saturday)...

A warm front extending from a surface low in the Gulf of Anadyr
will sweep across Southwest Alaska today bringing widespread light
snow to the region. Brisk wind and blowing snow has been observed
across the Kuskokwim Delta overnight, but should taper off later
in the morning as warmer air moves in from the southwest. This
southwest flow will become the dominant feature through the
forecast period as the region sits between a North Pacific ridge
and a trough moving southeast out of Russia. As a result, warm air
will mix in over the Kuskokwim first this afternoon, which may
cause some rain to mix in along the coast. On Saturday the warm
air will reach Bristol Bay and the interior with afternoon highs
pushing 40 degrees. This will bring some rain or at least a
rain/snow mix to low elevations from Aniak to Sleetmute, and south
into Bristol Bay. The western upslope regions of the Aleutian and
Kuskokwim Mountains, and Alaska Range will likely see substantial
snow.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 and 2: Friday
and Saturday)...

Ridging currently over the central Aleutians will push east
through Saturday as two shortwaves move east out of Siberia. Winds
are expected to remain below gale criteria with rain as the
predominant precipitation type. Moisture riding the top of the
ridge will be reinforced by the southern of the two shortwaves to
bring persistent rain to the Aleutian Chain by late Saturday
night.

&&

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

Bering Sea: Confidence is good through Tuesday. Sunday a low
pressure system moves into the eastern Aleutians and the AKPEN
with mainly small crafts, however Gales will develop out of bays
and passes south of the AKPEN late Sunday into Monday as colder
air filters south with a threat of freezing spray across the
eastern Bering and south of the AKPEN. A stronger front and low
pressure will move into the western Bering Sunday and move east
on Monday across the length of the Bering and Aleutians with
Gales expected with this system. Tuesday colder northwest flow
will develop with small crafts and possibly low end Gales moving
across the Bering with the threat of heavy freezing spray mainly
across the northern and eastern Bering.

Gulf of Alaska: Confidence is high through Monday and good
confidence Tuesday as winds and waves increase across the Gulf on
Monday and Tuesday. On Monday a front and low pressure system
moves into the Gulf with the low strengthening across the northern
Gulf on Tuesday. The strongest winds on Monday and Tuesday will
be northwest Gales out of bays and passes along the Alaska
Peninsula including near Kodiak and the Barren Islands, with seas
building. Also the threat of heavy freezing spray increases Monday
and Tuesday with these gusty northwest Gales from Cook Inlet and
south through the Barren Islands and the Shelikof Strait. Gales
are also possible south of the low across the southern Gulf Mon
and Tues.

&&

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

Monday and Tuesday, zonal west/east flow will continue across the
Bering through Alaska. This pattern will allow shortwaves and
fronts to track quickly through this fast upper level flow, with
chances of snow showers into early next week, especially for
higher elevations. A more potent, fast-moving shortwave and front
with colder air will move into the eastern Bering and Northern
Gulf on Monday. This feature will bring rain and snow from the
AKPEN to portions of Southcentral Alaska on Monday. It looks as if
this feature will stall over the northern Gulf as a second
shortwave drops from the Bering into the central Gulf Tuesday.
This will allow for colder air to filter in from the north later
Tuesday and Wednesday which will help to develop a deep trough
with below normal temperatures from mainland Alaska south into the
Gulf with a strong ridge developing across the Bering and
Aleutians Wednesday and Thursday. This pattern shift will keep the
threat of snow showers across the Copper River Basin and east of
Prince William Sound through Wednesday with drier conditions for
Southcentral for Thursday. Out west snow showers will continue
Tuesday through Wednesday morning across the eastern Aleutians and
AKPEN. By Thursday another quick moving front moves into the
Bering as the ridge shifts east with rain and snow.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...Winter Weather Advisory 155
MARINE...Heavy Freezing Spray Warning 130 138 185
	 	 Gale Warning 130 131
FIRE WEATHER...NONE.

&&

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