Area Forecast Discussion
Issued by NWS Anchorage, AK

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000
FXAK68 PAFC 241258
AFDAFC

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
458 AM AKDT Thu Jun 24 2021

.ANALYSIS AND UPPER LEVELS...
The longwave pattern features a broad trough over the Bering and
North Pacific. The jet core has a magnitude of 130 knots and it is
south of Kodiak this morning. On satellite imagery there is a
mature low with an occlusion spanning from Nikolski and into
western Alaska and the Western Alaska Range. Also on satellite
imagery there is a deep fetch of tropical moisture which is
discernible from Central Pacific to the Gulf Of Alaska and Prince
William Sound. The surface low anchoring this system is at 974 mb
near Unalaska. There is a tight pressure gradient field from Adak
to Yakutat associated with this low. During the night, gale force
winds were detected in ASCAT (Advanced Scatterometer) data.

&&

.MODEL DISCUSSION...
There is good consensus amongst the models with the synoptic
pattern over the next 48 hrs. As far as the localized winds and
the complex terrain...the NAM NEST (an NCEP high resolution
model) and the ARW (Advanced Research WRF produced by NCAR) are
the models of choice. Keep in mind that the tradeoff with the high
resolution models is that they do not go out as far in time.
Precipitation-wise there are some minor differences with timing
and storm total accumulations.

&&

.AVIATION...
PANC...With the front moving across the region the cigs have been
bouncing around at PANC and PAMR the past 12 hrs. As of 1127z the
lowest deck was at 800 feet and it was "broken". The high
resolution models do show the "Turnagain Arm Winds" kicking up
later today (approximately 22z) at PANC and slacken off between
12z-15z.

&&

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

The large low ins now centered over the Alaska Peninsula and the
front associated with this low has pushed into the Interior of the
state early this morning. The jest stream is running from near 30N
to the North Gulf coast east of Prince William Sound. While there
will continue to be rain along the north Gulf coast and in Prince
William Sound the heaviest rainfall will be east of the area in
Southeast Alaska today.

There will be a bit of a battle between the southerly and
northeasterly winds in Cook Inlet through tomorrow as the front
(and strong pressure gradient ahead of in) is now north of the
area, and the low center southwest of the Inlet. This is pulling
the strong Turnagain Arm winds down the Inlet this morning, but as
another wave approached the area, the winds will reverse and the
Turnagain Arm winds will make it into Anchorage for the afternoon.
There had been a question as to whether pressure rises behind an
upper level wave moving into Southcentral Alaska from the south
this evening would bring mush stronger winds than typical, but the
timing of this feature, and strength of it looks more like a
typical event. This holds true for other channeled terrain areas
around Southcentral as well. This wave moving into the region
this evening will increase the chance for rain for inland areas in
association with it. There may be just enough instability due to
it to produce an isolated thunderstorm near the Alaska Range in
the northwest Susitna Valley this evening.

This low near the Alaska Peninsula will be slow to move northward
and out of the area. This will cause persistent southerly flow
over the region into the weekend and keep the weather from
changing much.

&&

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

Unsettled weather continues across Southwest Alaska as a series of
upper level waves move from southeast to northwest across the
region. This will bring more clouds than sun, cooler temperatures
and a greater chance for rain. The best chance for wet thunderstorms
will be this afternoon and evening across the Kuskokwim Valley as
elevated instability will help drive convection. Otherwise, the
remainder of the period will be cloudy and wet.

&&

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

The pattern will remain unsettled as low pressure in the North
Pacific retrogrades northwestward into the Bering Sea. This low
will bring rain and showers to the central and eastern Aleutians
as well as the Pribilof Islands. Winds will remain below gale
force with no high seas expected.

&&

.MARINE (Days 3 through 5/Saturday through Monday)...
While there will still be some lows transiting the forecast area,
they look weaker than recent storms. Thus, expect winds less than
35 kts and seas less than 20 ft for the Day 3 through 5 period.

&&

.LONG TERM FORECAST (Days 4 through 7/Sunday through Wednesday)...
Medium range models are in much better agreement with synoptic
scale features for the first half of next week, providing some
better clarity on the expected weather. The key features include
a deep upper level low somewhere along the Aleutians and an
Arctic trough crossing the northern part of mainland Alaska. In
between, all solutions depict a short-wave ridge over the southern
mainland. This pattern supports unsettled weather across the
Bering Sea and Aleutians, likely with surface lows transiting the
area. For southern Alaska, the ridging (which differs from priors
days solutions which showed more troughing aloft) would provide
drier and warmer conditions. Sunday looks to be a transition day
out of the current cool cloudy and wet (in some places) pattern.
By Monday, it looks like the short-wave ridge is well-established
and would expect decreasing clouds. The question then becomes, how
long does this new pattern last? The GFS model is most aggressive
in shifting the Aleutian low eastward, pushing rain into
Southwest Alaska Tuesday through Wednesday. The ECMWF/Canadian as
well as ensembles all support holding onto the ridge longer. In
any case, it looks like a higher likelihood for Southcentral to
remain warmer/drier through at least mid week.

&&


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

&&

$$

SYNOPSIS AND MODEL DISCUSSION...PJS
SOUTHCENTRAL ALASKA...EZ
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...ED
MARINE/LONG TERM...SEB


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