Area Forecast Discussion
Issued by NWS Anchorage, AK

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000
FXAK68 PAFC 230034
AFDAFC

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
434 PM AKDT Tue Jun 22 2021

.ANALYSIS AND UPPER LEVELS...
A high amplitude pattern is in place, with a large vertically
stacked low digging southeastward across the north-central
Pacific and a ridge downstream over the east Pacific. Direct
impacts from this mature storm system are minimal, with areas
of light rain and small areas of small craft advisory level
winds along the Aleutians. More significantly, a short-wave
trough rounding the east side of the low circulation combined
with a subtropical jet streak and area of upper level diffluence
to initiate cyclogenesis over the North Pacific. This low is
deepening as it tracks northward toward the Alaska Peninsula and
Gulf of Alaska. The upper level support for this system is quite
impressive for this time of year. This unseasonably strong storm
will be the focus for weather over the southern mainland over the
next 36 to 48 hours.

For the southern mainland of Alaska, cyclonic flow aloft
persists, but with little in the way of organized forcing to
produce precipitation. Weather is generally dry, but with
considerable cloud cover across the region. The sun is working
on eroding some of these clouds, but with a moist environment
and weak instability, cumulus clouds tend to quickly pop up
shortly after an area clears out.

&&

.MODEL DISCUSSION...
Models are in good agreement with most features. One notable
difference is the track/timing of a short-wave trough crossing
the Gulf and Southcentral Thursday through Thursday night. This
will impact the wind forecast, especially for gap winds along the
Gulf Coast and into Southcentral Alaska. Notably, expect a strong
Turnagain Arm jet to bend into Anchorage as this passes through,
so there is quite a bit of uncertainty in timing of the winds.

&&

.AVIATION...
PANC...VFR conditions will persist. Winds are the primary forecast
challenge. Southeasterly Turnagain winds have moved into the
terminal this afternoon and will persist into this evening.
On Wednesday, a strong front will lift northward across the Gulf,
with a strengthening Turnagain Arm jet. However, strong north-
south pressure gradients will force the winds to bend south as
they exit Turnagain Arm, keeping the winds out of the airport.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 through 3: Today
through Friday afternoon)...

Skies will continue to clear across Southcentral this evening as
an upper shortwave departs to the north. Attention will quickly
turn to an unseasonably strong front moving into the Gulf late
tonight. Gusty easterly winds and locally heavy rain are expected
over Kodiak Island through Wednesday, with rainfall totals likely
exceeding 2 inches. The front will track farther northward
Wednesday afternoon and evening and bring similar impacts to
coastal Prince William Sound into Thursday morning. A potent
shortwave trough will move over Cook Inlet Thursday
afternoon/evening, leading to a spike in surface wind speed. West
Anchorage, including Ted Stevens, could potentially see 35 to 45
mph southeasterly gusts in this timeframe. Winds will gradually
diminish by Friday morning as upper flow slightly weakens.

Precipitation will generally be confined to the coast, however
given the strength of the front and the overall moist environment,
overrunning is possible and thus brief periods of rain are
possible across Anchorage and the Mat-Su. The best chances for
this will be Wednesday and Thursday evenings. As such, high
temperatures will be slightly cooler than previous days.

&&

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

Models are on track with the arrival of the frontal system to the
south of AKPEN this evening. Short impulse waves from the upper
low connected to the front will bring increased rainfall through
the corridors of Bristol Bay, lower Kuskokwim Valley and the
Southwest coast in the next couple days. Orographic lifting
combined with isolated upper level waves will produce moderate to
heavy rainfall more in between the western portion of Bristol Bay
and the easternmost section of Kuskokwim Delta on Wednesday and
Thursday. Essentially, strong winds and gusty conditions
associated with the front will be felt strongly over the AKPEN
tonight, and over Bristol Bay starting tonight through at least
Thursday night. High temperatures in the upper 50s to upper 60s
will linger over much of the region except for Bristol Bay, high
temperatures in the lower 60s will fall in the 50s by Friday.

&&

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

Two separate lows merging over the Eastern Aleutians by Wednesday
afternoon will meander over the Eastern Aleutians before leaping
northeast toward the eastern Bering south of Nunivak Island by
Friday. This large scale weather pattern will maintain gales over
the Eastern Aleutians, Bristol Bay, and the waters south of the
AKPEN on Wednesday, with the potential for gales to continue into
Wednesday is feasible should the front and low continue to
strengthen into Wednesday afternoon. Large wave heights up to 12
to 14 ft will move through the south and northern waters of AKPEN
between Wednesday and Thursday night. Essentially, unsettled
weather will persist for the Aleutian Chain and the eastern Bering
through the short term.

&&

.MARINE (Days 3 through 5: Friday through Sunday)...
The remnants of the big storm arriving tonight/Wednesday will
linger in the eastern Bering Sea Friday. There will still be some
potential for gale force winds on the eastern periphery of this
low, in the Bristol Bay/Alaska Peninsula area. Beyond Friday, this
system will weaken allowing winds to diminish. Otherwise, expect
a break from the recent storminess over the weekend, with winds
less than gale force across the region.

&&

.LONG TERM FORECAST (Days 4 through 7: Saturday through Tuesday)...
Looking at this weekend through early next week, a long-wave
trough will persist across the Bering Sea/Aleutians on into
western Alaska, with ridging downstream over western Canada/CONUS
and the east Pacific. While models all show the same general
pattern, there are differences in handling of individual features
embedded within the trough. This pattern generally supports cool
and wet weather. The picture becomes blurry early next week, when
some solutions indicate rising heights over southern Alaska, with
potentially drier/warmer conditions. Other solutions continue the
more "troughy" (cool and wet) pattern from the weekend.
Predictability for any given day is low at this point, so stay
tuned as we get closer in time.

&&


.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...Storm: 131 138.
Gale: 119 120 130 132-137 139 150-165 180 351 352.
FIRE WEATHER...NONE.

&&

$$

SYNOPSIS AND MODEL DISCUSSION...SEB
SOUTHCENTRAL ALASKA...AP
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...CB
MARINE/LONG TERM...KZ/SEB


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