Area Forecast Discussion
Issued by NWS Anchorage, AK

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000
FXAK68 PAFC 190043
AFDAFC

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
443 PM AKDT Mon Oct 18 2021

.ANALYSIS AND UPPER LEVELS...

A broad mid to upper trough wrapped to a diffused upper low near
Kodiak will continue to bring steady light to moderate rain over
Kodiak Island and the northern Gulf, including Western Prince
William Sound. A barrier jet meandering over the northern Gulf has
generated strong easterly winds with high end gales near
Middleton Island and mainly south of Prince William Sound today.
Meanwhile, a vast upper ridge runs across the Bering to Southwest
Alaska then turns east through Southcentral to beyond Wrangell
Mountains. Multiple shortwaves over the Alaska Peninsula and
across the Gulf enhances the potential for increased rain, clouds
and gusty winds in those areas.

&&

.MODEL DISCUSSION...

Synoptic agreement in the short term is pretty good this
afternoon. Guidance has converged and agrees on how the
aforementioned diffuse Gulf low will elongate before sliding north
into Prince William Sound. Translated down to the surface, this
low will move inland near Seward tomorrow morning. This is a shift
from previous guidance that now places the low farther west. This
track change also increases winds along Turnagain Arm, a point
where all models are agreeing. Deeper into the work week,
guidance, surprisingly, tells a very similar story with the next
system moving in from Japan. By forecast hours 72-78, there are
minor placement errors amongst the big model members, with the
overall trend that seems to be set with a strong low moving into
the Bering in that time.

&&

.AVIATION...

PANC...VFR conditions will persist, with gentle northerly winds
continuing through today and Tue morning. Tue evening, Turnagain
Arm winds will be increasing. For the majority of the event, winds
should remain off of the airfield, but there may be a window at
12z on the 20th where winds may bend into the airfield for a 3-6
hour period. There is a low probability that ceilings may lower
towards low end MVFR levels around the same timeframe.

&&
.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 through 3:
Tonight through Thursday afternoon)...

A nearly stationary front in the Gulf will continue to bring high
end gale force winds, and elevated seas at times near the coastal
areas before subsiding to small crafts by Tuesday night. A moist,
easterly flow pattern associated with the frontal boundary will
also keep cool and wet conditions ongoing over the next couple of
days especially in Prince William Sound.

Meanwhile, an area of low pressure will form along the front and
move south of Cordova tonight. The latest operational model runs
are coming into decent agreement with a more westward track of
the low by Tuesday evening, before weakening and moving across
the Kenai Peninsula by Wednesday morning. As it does so, a
tightening pressure gradient will ramp up winds across the
forecast area with stronger gusts expected over the hillside and
higher elevations.

Additionally, the low will push some of the precipitation further
inland beginning on Tuesday with rain/snow mix in the valleys and
snow in the surrounding elevations. The Matanuska Valley,
Anchorage Bowl, and western Kenai Peninsula will remain mostly dry
with the downslope easterly flow, but a rain or two cannot
completely be ruled out especially for Wednesday afternoon and
evening if the winds weaken and shift more southerly. Thereafter,
a secondary low will form in the eastern Gulf on Wednesday
evening, bringing another round of moderate to heavy rain in PWS
and the eastern Kenai Peninsula through Thursday afternoon.

&&

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

A low in the northwestern Bering will bring unsettled weather to
the Southwest through Wednesday. Its front is already beginning to
push ashore in the Kuskokwim Delta region this evening, with the
first returns already visible on the Bethel radar. Precipitation
should begin as snow with temperatures in the Lower Kuskokwim
Valley and Delta region hovering around or below freezing.
However, warm air advection is expected with the passage of the
front. Snow should turn to rain as the front progresses inland
through Tuesday afternoon. Further south, at locations like
Dillingham and King Salmon, warm air aloft combined with a warmer
pre-existing airmass will keep precipitation as rain. Overall,
precipitation is expected to be light with minimal snow
accumulations. Behind the front, expect drier conditions and gradually
cooling temperatures Wednesday and Thursday.

&&

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

Tonight, a series of fronts associated with a low in the
northwestern Bering Sea track eastward across the Aleutian Chain,
bringing showers and gusty winds. Gale force winds enhanced by
cold air advection behind the fronts will sweep through the
Aleutians, beginning in the west tonight and reaching the eastern
islands Tuesday night. As the intensity of the cold air advection
diminishes, winds will follow suit through Wednesday morning. Snow
or rain/snow showers are possible over the Pribilofs on Tuesday
night with the advancing cold air. However, rain showers are
expected for the remainder of the Aleutians as heat from the
warmer ocean waters modifies the air mass. Wednesday night, a
second low approaches the western Aleutians from the North
Pacific. This low will have the potential to produce storm-force
winds as it crosses the islands into the Bering.

&&

.MARINE (Days 3 through 5/Thursday through Saturday)...

Bering/Aleutians

Forecast confidence is moderate during the 3-5 day period as a
strong low pressure system moves through the southern Bering Sea
on Thursday and Friday. Minor differences exist between guidance
with respect to the placement and intensity of this low. There is
high confidence that widespread gale force winds will occur during
this period. In addition to the strong winds, large long period
northwesterly swell is expected along the coastal waters on the
north side of the Aleutian Islands Thursday and Friday. These
winds and seas will gradually ease and abate on Saturday.

Gulf of Alaska

Forecast confidence remains above average for Thursday with winds
remaining under gale force and no high seas. Confidence decreases
on Friday as the next low moves in from the North Pacific. Gale
force winds are possible along the coastal waters throughout the
northern Gulf on Friday and Saturday.

&&

.LONG TERM FORECAST (Days 4 through 7/Friday through Monday)...

A cloudy, cool and wet pattern is expected for Southcentral Friday
through Monday as upper-level troughing extends from the northern
Bering Sea into the central Gulf. This orientation of the upper
trough will allow for moisture to enter Southcentral as the
trough-axis remains southwest of the Kenai Peninsula and thus
resulting in broad south-southeasterly flow from the Gulf. With
respect to precipitation type, the chance for snow increases with
elevation.

The Bering/Aleutians will be in a cloudy and cool pattern as broad
upper level troughing continues to extend across the region.
Strong northwesterly gap winds are expected in the eastern
Aleutians and western Alaska Penunsula on Friday and Saturday in
the wake of a strong low pressure system moving into the Gulf.
These winds will eae Sunday and Monday.

&&


.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...Gale Warning: 119-120, 125, 128, 131, 140, 155, 170-179,
                       185, 351, 411-414.
FIRE WEATHER...NONE.

&&

$$

SYNOPSIS AND MODEL DISCUSSION...SS
SOUTHCENTRAL ALASKA...MF
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...CQ/PS
MARINE/LONG TERM...ED


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