Area Forecast Discussion
Issued by NWS Anchorage, AK

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000
FXAK68 PAFC 241558 CCA
AFDAFC

Southcentral and Southwest Alaska Forecast Discussion...CORRECTED
National Weather Service Anchorage AK
658 AM AKST Fri Jan 24 2020

.ANALYSIS AND UPPER LEVELS...

A negatively tilted ridge stretches from eastern Siberia, through
the Pribilof Islands, into the eastern Aleutians and northern
Pacific. Flanking this ridge is a pair of lows, at the surface and
aloft, located south of Shemya and over the northern Gulf
respectively.

&&

.MODEL DISCUSSION...

The models remain in excellent agreement through the weekend in
their mid-level forecasts through the weekend, before starting to
diverge early next week. Closer to the surface, the models also
remain in good agreement from the tip of the Alaska
Peninsula/Southwestern coast and points west of there.

The real question is for the Gulf. The GFS surface plots have
reverted back to an unusually deep low (943 mb) coming into the
southern Gulf Wednesday morning. Meanwhile, the Canadian has a 969
mb low over Whittier, and the European projects a 975 mb low
southwest of Sitka with another 970 mb low a little southwest of
Seward.

The further west track would be a more favorable position for
snowfall across much of Southcentral, and eastern portions of
southwest Alaska. Stay tuned.

&&

.AVIATION...

PANC...VFR conditions will prevail through the period, with light
winds continuing through the evening. Northeasterly winds begin
to gust to near 20 knots after 04z. We also inserted a vicinity
mention, as the morning analysis shows the Gulf low further west
than forecast. Doppler radar is also showing some flurries or
very light snow moving into the city/terminal. This may linger
into the afternoon.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 and 2...Fri and
Sat)...

The next few days will be dominated by a low pressure center in
the northern Gulf of AK. The low is meandering around over top of
Middleton Island. To the west of the center it is pulling cold air
down through the AK Range into much of Southcentral. To the east
of it, the low is able to pull moisture up from the Gulf and
spread it into locations stretching from Cordova up through
Eureka and over towards the Portage Valley. This set up will hold
through the morning hours leaving Girdwood and Portage vulnerable
to snow showers. Even though some of these showers are creeping
along the Chugach, we don`t expect more than flurries to make it
into the Anchorage Bowl. By this afternoon, all models drift the
low center south and east away from the mainland. This should
allow skies to at least partially clear with a staunch offshore
gradient. The cold air will continue to make for gusty winds
through many of the typical gaps. These winds will also help
create heavy freezing spray over many of the marine zones, so
mariners should check the forecast for their local areas.

By Saturday, model agreement with the low center starts to wane.
It looks as if it will drift back towards the coast and bring a
slightly better chance of snow showers back into Cordova once
again. The other area of interest is just south of Kachemak Bay.
The cold air over the warmer waters will allow for a few bands of
"ocean-effect" snow to set up. Models are now indicating that
these bands could slide into the north and west side of Kodiak
Island and work their way south through the day. While most of the
snow should stay clear of Kodiak City, some of the more remote
locations on the island could pick up a few inches of
accumulation. Temperatures into the weekend will be highly
dependent upon cloud cover and winds. Any locations that can clear
out and keep calm winds will see their temperatures plummet during
the overnight hours.

&&

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

The overall synoptic pattern remains the same, with a highly
amplified upper ridge over the eastern Bering and a deep upper low
centered over the northern Gulf.. Southwest Alaska lies in
between these two features, which is leading to strong northerly
winds aloft and thus colder temperatures moving into the region.
While the strongest surface winds will remain offshore south of
the Alaska Peninsula, they will still be gusty enough over land
that Wind Chill Advisories remain in effect through noon Sunday
for the Bristol Bay and Kuskokwim Delta areas. The temperature
forecast remains challenging given subtle shifts in the
aforementioned pattern through Saturday, as cloud cover may
progress slightly to the west at times. However, the entire upper
low will shift west by Sunday and thereby cause temperatures to
decrease further and potentially lead to scattered onshore snow
showers.

&&

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

A ~970 mb compact low is currently tracking south of Shemya. Storm
force winds are likely to its east along the associated front as
well as moderate rain/show showers across the western Aleutians.
This will continue through Saturday before the low becomes
vertically stacked and weakens near Kamchatka. Another low will
approach from the North Pacific Sunday. Its front will bring another
round of gusty easterly winds and rain/snow to the region. Strong
upper high pressure will persist over the central and eastern
Bering/Aleutians through Sunday.

&&

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

Gulf of Alaska:

An occluded low and a surface low will persist over the Gulf of
Alaska Saturday, Sunday and Monday bringing moisture to the region.
Strong high pressure over the mainland coupled with the low
pressure in the Gulf will produce strong offshore flow winds,
especially near the Barren Islands and Kamishak Bay. Gale force
winds and heavy freezing spray possible.

Bering Sea and Aleutians:

A strong low south of the western Aleutians will keep widespread
gales with the possibility of isolated storms across the central
and western Bering Saturday and Sunday. Freezing spray will
continue to impact portions of the Bering. Winds will decrease by
Monday.

&&

.LONG TERM FORECAST (Days 4 through 7)...

Looking at the synoptic pattern, expect low pressure over the
Gulf of Alaska and south of the Aleutians with a dense cold
airmass building up over the mainland. Below normal temperatures
will continue for western Alaska and southcentral Alaska. This
setup will result in enhanced gap winds through the coastal
mountains with precipitation mainly along the coastal regions of
the Gulf.

&&


.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...Storm Warning 411
         Gale Warning 121 127 130 131 132 138 150 155 173 174 175 176
         177 178 185 412 413
         Heavy Freezing Spray Warning 121 127 129 130 132 138 139 141
         150 160 165 179 180 185
FIRE WEATHER...NONE.

&&

$$

SYNOPSIS AND MODEL DISCUSSION...PD
SOUTHCENTRAL ALASKA...MSO
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...AP
MARINE/LONG TERM...PJS


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