Area Forecast Discussion
Issued by NWS Anchorage, AK

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000
FXAK68 PAFC 270044
AFDAFC

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
444 PM AKDT Mon Jul 26 2021

.ANALYSIS AND UPPER LEVELS...

The upper level pattern is active today with a ridge of high
pressure building through the Western Gulf and into Southcentral
AK. A weak low continues to spin in place in the Eastern Gulf of
Alaska. Out west, a short wave trough is pushing through Southwest
AK and strong northwesterly flow is behind it. At the surface,
high pressure building into Southcentral is causing the typical
summer low stratus to develop in the Western Gulf. It is also
producing low stratus inland that is burning off in the afternoon.
In southwest AK, the upper level trough is presented as a front at
the surface that is producing light rain. Strong winds behind it
are beginning to produce gap winds through the Aleutians. While it
is an active pattern, much of it results in minor weather concerns
and thus things are generally quiet.

&&

.MODEL DISCUSSION...

Models are in good synoptic agreement through the short term. Some
adjustments maybe needed for wind speed through gaps in the
Aleutians and coastal areas of Southcentral Alaska. However, these
adjustments will be minor and little adjustment needed away from
model data, save for localized winds. Thus, high confidence in
numerical data through the short term

&&

.AVIATION...

PANC...VFR conditions and light winds will persist. An MVFR
stratus deck is expected to develop overnight. We are not
forecasting a ceiling to develop at this time, however there is a
chance that a ceiling could develop.

&&

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

The jet stream is highly amplified. There is a jet core extending
from Kamchatka to the Seward Peninsula, a weak jet core south of
Unalaska and another jet core pushing into British Columbia. Lower
in the atmosphere at (500 mb) there is a weak ridge over the
Copper River Basin, Anchorage and Kenai. All the while at 500 mb
there is a closed low over the eastern Gulf and a broad closed
arctic low from Kamchatka to the Chukchi Sea with multiple
shortwaves embedded in it. By Tuesday, shortwaves propagate
through the 500 mb high but they don`t seem to have an impact on
the sensible weather other than increasing cloud coverage. The
models show dry weather for most of Southcentral tonight, Tuesday
and Wednesday. However, the high resolution models are pinging
into enhanced winds over the Barren Islands, Shelikof Strait, and
Turnagain Arm.


&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 through 3: Tonight
through Thursday evening)...

Mostly cloudy skies will persist over the region this evening in a
moist, onshore flow. A series of upper troughs will bring
scattered showers along the northern portions of the Kuskokwim
Delta on Tuesday. A weak ridge will build into the Bristol Bay
area at the same time, leading to partial clearing. Benign
conditions will continue over Bristol Bay into Wednesday under the
ridge. A front will approach the Kuskokwim Delta coast by
Wednesday morning and will slowly move onshore by evening. Winds
will increase and are expected to be strongest along the immediate
coast. Rain will continue over the area Thursday as the front
remains nearly stationary.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 through 3: Tonight
through Thursday evening)...

A broad upper level trough and associated low over eastern Russia
will lead to widespread rain tracking west to east across the
northern Bering through Wednesday. While much of the Aleutians
look to remain dry, gusty southerly winds out of bays and passes
will develop Tuesday afternoon and continue through Wednesday
generally between Nikolski and Nelson Lagoon. Winds will diminish
Thursday under another upper trough, with rain extending
southwestward from Bristol Bay through the central Aleutians along
a front.

&&
.MARINE (Days 3 through 5:Thursday through Saturday)...

For the Gulf of Alaska, expect winds less than 35 kts and seas
less than 20 ft for the Day 3 through 5 period. Conditions will
generally be the same for the Bering Sea as well. However, some
lingering gap winds will be present along the Eastern Aleutian
Islands Thursday with a front moving through the area. We can also
expect small craft advisories along the Southwest Coast as well.

&&

.LONG TERM FORECAST (Days 3 through 7: Thursday through
Monday)...

There is general agreement that longwave troughing maintains in
the Bering Sea, with a more dynamic pattern over Southcentral AK.
This longwave is really the anchor of the weather pattern, with
high pressure giving way to more a transition setup for southcentral
late in the week. Models are at least in decent agreement on the
large scale pattern, with a blend of the GFS and ECMWF being a
good starting point. This was coordinated with WPC so will be
leaning on them for the long term forecast today. Overall decent
agreement in the models on the synoptic scale, with specific
features yet to be dialed in. So, moderate forecast confidence.


&&


.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...NONE.
FIRE WEATHER...NONE.

&&

$$

SYNOPSIS AND MODEL DISCUSSION...BB
SOUTHCENTRAL ALASKA...PS
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...AP
MARINE/LONG TERM...BB


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