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000
FXAK68 PAFC 250102
AFDAFC

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
502 PM AKDT Sun Sep 24 2023

.ANALYSIS AND UPPER LEVELS...
High pressure remains anchored over the Alaska mainland, as a
300mb jet dives south of the Aleutians and recurves north over
the Pacific Northwest and Canadian coastlines. Two low pressure
centers are supported by this upper jet: one north of the western
Aleutians that has breezy north to northwest winds embedded
within it; while the other progresses northward along the eastern
Gulf, which will bring lowered ceilings and breezy conditions to
the normal gap regions of Southcentral by early Monday. Otherwise,
quiet, with a few showers still lingering from a weakening low
south of the Kenai Peninsula, and an ever weakening front along
the Southwest coastline.

&&

.MODEL DISCUSSION...
Models continue to be in good overall agreement through mid-
week. By the end of the week, model discrepancies become apparent
between the progression of two lows: one dropping into the Bering
from the west; the other, moving up the southeast coastline into
the Gulf. Discrepancies in timing and strength have lead to
lowered confidence in the details, though high confidence in these
two lows bringing unsettled weather back to southern Alaska is
assured.

&&

.AVIATION...
PANC...VFR conditions and light winds will persist.

&&

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

A very quiet (and at least somewhat sunny) stretch of Fall
weather is still on tap for most of Southcentral through midweek.
In the near term through tonight, a few pop-up showers that have
developed with daytime heating over and near the Chugach,
Talkeetna and Kenai Ranges should quickly die off as the sun sets.
Meanwhile, a very weak low will drift east of Kodiak Island later
tonight, perhaps pushing a couple rain showers into the area as
the low fully loses integrity.

Looking out into the first half of the week, a couple changes to
the prevailing pattern are anticipated, but upper level flow will
remain very weak while the Pacific jet remains well to the south
of us. On Monday, the weak upper ridge currently extending into
much of Southcentral from the Interior will shift north, allowing
a North Pacific low spinning a ways offshore from British Columbia
to lift slowly north towards Southeast AK through Tuesday. A as
result, lowering surface pressure over the Gulf will begin to
support an offshore gradient focused along the north Gulf Coast.
In addition, a negatively-tilted shortwave moving into the western
Gulf on Tuesday will help reinforce a surface trough across the
northern Gulf. This will lead to a prolonged period of low level
offshore flow and gap winds through the typically favored spots
along the coast between the Kenai Peninsula and Prince William
Sound vicinity. However, due to the lack of upper level support,
none of these winds will become particularly strong and gusty,
most likely remaining below small craft thresholds through
Wednesday. Meanwhile, stronger northwesterlies will develop behind
the trough moving into the Gulf near the Barren Islands and
portions of Kodiak Island on Tuesday and persist into Wednesday.

Aside from the winds over the Gulf, conditions will remain very
calm, and dry for September standards, with negligible
precipitation chances for most of the outlook area through
Wednesday. The developing offshore winds should also help clear
out what scattered low to mid clouds we have left later tonight,
at least up until the aforementioned shortwave trough moves into
Southcentral late Tuesday into Wednesday.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA/BERING SEA/ALEUTIANS (Days
1 through 3: Tonight through Wednesday)...

A weak low centered several hundred miles north of Kiska Island is
bringing gusty westerly winds and rain showers through the
western and central Aleutians this evening. To the east,
relatively calmer and drier weather is being experienced as a weak
upper- level trough over the eastern Bering Sea and Southwest
Alaska is leading to mostly cloudy conditions and isolated rain
showers. The low in the western Bering is forecast to drop
southeast across the Bering Sea, its front sweeping along the
Aleutians tonight bringing light rain, with winds increasing out
of the west to around 25 to 30 mph after the frontal passage. The
front reaches the southern tip of the Alaska Peninsula on Monday
as the low weakens and dips into the North Pacific. A weak ridge
of surface high pressure spreads across the Bering Sea for the
remainder of Monday, limiting any precipitation to isolated light
rain showers as winds diminish.

Monday night, southerly winds increase in the western Aleutians
as a Kamchatka low begins to push into the western Bering. Winds
in association with this low are likely to remain below gale force
as it pushes east on Tuesday. Rain along its front reaches the
Pribilof Islands on Wednesday as the low center begins to track
into the northern Bering Sea. Southwest Alaska can continue to
expect quiet, partly to mostly sunny skies, with a slight chance
of isolated showers until the low in the northern Bering brings
increasing winds and rain to the Kuskokwim Delta coast late on
Wednesday.

&&

.LONG TERM FORECAST (Days 4 through 7: Thursday through Sunday)...

Forecast models agree through mid-period, but starts to diverge
in positions and strengths by Sunday. High pressure that covered
most of the Interior bringing variable cloudy skies will retreat
further towards the Canadian Border. A well developed long wave
trough extends from a low in the Arctic through the Western Bering
progresses into Mainland Alaska by the end of the period. A
series of lows will traverse the Aleutians into Southwest and
Southcentral Alaska, bringing locally heavy rains and gusty winds
with each center. The exception to this pattern will be a deeper
low moving into the Central Aleutians late Thursday, and into the
Northern Alaska Peninsula by Sunday.

As a result, chances for rain increase toward late week along the
Gulf coast, with some potential for offshore small craft winds
through gaps along the coast as well. Gale force winds pushing its
front across the Aleutians Friday. However, the exact track of
this low is fairly uncertain by the end of the period. The general
trend in the pattern suggests increasing chances of widespread,
steady rainfall over Southwest Alaska up to the North Gulf Coast
going through the weekend.

&&
$$

SYNOPSIS AND MODEL DISCUSSION...AB
SOUTHCENTRAL ALASKA...AS
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...CQ
LONG TERM...MK