Area Forecast Discussion
Issued by NWS Anchorage, AK

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483
FXAK68 PAFC 170019
AFDAFC

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
419 PM AKDT Fri Apr 16 2021

.ANALYSIS AND UPPER LEVELS...A quasi-Rex Block pattern is trying
to take shape over the domain. The first ingredient a building
area of high pressure over the Bering and SW Alaska. The second
ingredient is a vertically-stacked upper level low complex south
of Sand Point. As the high shifts east and the low dips south, it
will allow for these two features to work in tandem to slow any
progress to the pattern.

At the surface, a frontal boundary is bringing rain and gusty
southerly winds through the Western Aleutians. Near Kodiak, the
remnants of a wave coming around the low are bringing scattered
rain showers from Akhiok to Chignik. Across much of the rest of
Southern AK, offshore flow is leading to mostly clear skies
allowing for a quick warm up under abundant April sunshine.

&&

.MODEL DISCUSSION...Models are in very good agreement lending to
high forecast confidence. The main issues remain some of the
details regarding the large diurnal temperature swings, especially
as it relates to any cloud cover. Fog may become an issue as we
go into the weekend with warmer air aloft trying to nose in. The
best chance for any formation would be near coastal areas/open
water sources.

&&

.AVIATION...
PANC...VFR conditions and light winds will persist. There is an
outside chance for some fog to form along Knik Arm and drift over
the terminal in the morning. However, due to the dry nature of the
airmass, confidence in any fog (or stratus) formation is low.

&&

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

A Rex Block currently extends across the North Pacific with the
upper level ridge extending over Southcentral Alaska. This pattern
will continue to bring sunshine and warm temperatures across the
area over the next 3 days. As skies will remain fairly clear at
nighttime, fog is likely in coastal locations. Showers will move
across Kodiak tonight. Showers will remain rain near the coast and
snow in the higher elevations.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 and 3...Tonight
through Monday afternoon)...

Southwest Alaska is expected to remain quiet and dry through the
duration of the forecast period. Temperatures will mainly range
from the 40s and 50s inland to 30s and 40s closer to the coast.
Overnight lows will be able drop substantially from daytime highs
due to very good radiational cooling the next few nights due to
clear skies and light winds. Rapid snowmelt is expected to
continue for the next couple days with any melting that takes
place during the day refreezing overnight. The best chance for any
sort of rain shower activity will be mainly on a line from Egegik
to King Salmon on southward down the Alaska Peninsula to Port
Heiden and Pilot Point over the weekend into early next week.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 and 3...Tonight
through Monday afternoon)...

First, Semisopochnoi Volcano is currently active near Adak. Please
see marine weather statement for further details on this.

Next, a gale force frontal boundary will continue to slowly
progress eastward slowing down and stalling across the central
Bering Sea through Sunday morning. Model guidance shows this front
stalling and dissipating (frontolysis) Sunday morning near or
right over Adak. High pressure will then dominate the Western
Aleutians and the western Bering from Sunday morning through the
remainder of the forecast period.

A couple of upper level shortwaves will move northwestward on the
northern periphery of an upper level low over the North Pacific
over the weekend and into early next week. A few areas along the
Aleutian Chain namely Dutch Harbor, Cold Bay, and Sand Point may
see a rain/snow mix on Saturday/Saturday night but snow
accumulation is expected to be none for populated areas. Mainly
rain is then expected the remainder of the forecast period with
any precipitation as the air mass will be too warm.

&&

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

Bering Sea/Aleutians:

A long-wave from the western Gulf enters the Bering and Aleutians
on Monday morning, then continues west-northwest through
Wednesday. Two separate North Pacific lows will bring strong
northerly gales with higher gusts near the Bays and Passes of the
Aleutians and AKPEN during the forecast period.

Gulf of Alaska:

A stacked North Pacific low will bring long period southerly
swells and seas up to 13 ft across the Gulf Monday and Monday
night, followed by an upper ridge by Tuesday morning. Relatively
quiet conditions are expected after Monday night.

&&

.Long Term Forecast (Days 4 through 7: Tuesday through Friday)...

A "Rex Block" Pattern will persist as the North Pacific low
continues northwestward across the Bering Sea through Wednesday.
This same low will enter the Gulf of Anadyr by Wednesday night,
leading the upper high from the Arctic to shift south-
southeastward toward the central Bering. Essentially, the high
will predominate the Bering Sea from Thursday night through
Friday afternoon. As a result, anticipate a quiet forecast period
mainly after Tuesday night.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...Gale 177 178 185.
FIRE WEATHER...NONE.

&&
$$

SYNOPSIS AND MODEL DISCUSSION...MSO
SOUTHCENTRAL ALASKA...ED
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...MV
MARINE/LONG TERM...CB



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