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126
FXAK68 PAFC 270048
AFDAFC

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
448 PM AKDT Sun May 26 2024

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

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This evening, Southcentral Alaska sits in a col (saddle point)
between a weakening low in the Gulf of Alaska, an upper-level low
centered over northwestern Alaska, a ridge in the Canadian
Arctic, and a ridge in the Bering Sea. This will allow weak flow
and weak features to dominate the weather for the next several
days. Satellite imagery shows one such feature, a weakening
easterly shortwave, currently crossing from the Copper Basin into
the Susitna Valley, with associated cloud cover and shower
activity. The relatively warm and somewhat unstable conditions
will allow for the continued development of isolated to scattered
showers across much of inland Southcentral this afternoon/evening.

Across the western half of Southcentral, storm motion is directed
toward the southwest, which would suggest some potential for
showers developing in the foothills of the Talkeetna Mountains to
push across the Matanuska Valley and into Anchorage later this
evening/tonight. However, conditions currently look similar to
yesterday, with stable air in the vicinity of Cook Inlet once
again, which would be expected to prevent or quickly weaken any
showers attempting to approach Knik Arm. It is worth noting,
though, that there is decent support from high-resolution model
guidance for convective development in the vicinity of the
Talkeetnas tracking south into the Matanuska Valley and persisting
into Anchorage, making for a tricky forecast this evening.
Satellite and radar show developing showers over the Talkeetna
Mountains, likely aided by the support of the shortwave crossing
into the Susitna Valley. As a result, the current forecast favors
the model guidance and depicts numerous rain showers in the
Matanuska Valley this evening, with a chance for showers to make
it to Anchorage later in the evening and overnight as the
slow westward motion of the shortwave aloft allows for continued
enhancement of lift.

Focus then shifts east for Monday and Tuesday. A series of upper-level
easterly shortwaves will track into the Copper River Basin from
Yukon, bringing periods of primarily stratiform rain across the
basin and into the eastern and central Chugach Mountains,
potentially including eastern Prince William Sound. At this
point, there still is a significant amount of uncertainty
regarding the exact timing of several easterly waves, but
confidence is good that somewhere in the realm of half an inch to
an inch of rain will fall in the central and eastern Copper River
Basin on Monday and Tuesday. Higher amounts will be possible north
of the Wrangells.

For the western half of Southcentral, weak ridging will sit aloft,
preventing the progression of easterly waves. As a result,
conditions will remain similar to today and yesterday, with high
temperatures around 60, and partly cloudy skies with potential for
isolated showers produced by daytime heating driven instability.

Tuesday night, a front off a low in the Bering Sea nudges into
the southwestern Gulf, bringing rain to Kodiak Island into
Wednesday. A weak coastal ridge may allow for southeasterly gap
winds through Turnagain Arm and Knik Arm to intensify as well
mid-week.

- Quesada
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&&


.SHORT TERM FORECAST SOUTHWEST ALASKA, THE BERING SEA AND THE
ALEUTIANS (Days 1 through 3)...

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Weak northerly flow and drier conditions are gradually filtering
into Bristol Bay today. Afternoon highs are expected to warm into
the upper 50s with low 60s possible for parts of the Lower
Kuskokwim Valley and Greater Bristol Bay areas. Solar heating and
just enough instability will cause showers and isolated wet
thunderstorms to develop along the Alaska Range this afternoon
into the evening hours.

In the Bering and for much of the Aleutians, widespread low
stratus and areas of fog may develop in the early hours of Monday
morning due to subsidence created by the transient ridge of high
pressure. On the western side of the Bering, a Kamchatka low is
bringing a front across the Central Aleutians with increasing
southeasterly wind gusts up to gale force. An elongated area of
low pressure is expected to form along the front on Monday as the
ridge begins to break down over the Bering. Unsettled conditions
are forecast over the Eastern Aleutians and Lower Alaska Peninsula
on Monday, with low pressure becoming more amplified over the
Bering on Tuesday.
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&&

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

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By Thursday, a low pressure system will center itself near the
Alaska Peninsula and stay situated until midday Friday. Widespread
precipitation across Southwest is possible until a deep upper-
level trough enters the Western Bering on Friday and causes the
low to dissipate. The new trough will traverse across the
Aleutians through the weekend before ending up near the western
Gulf of Alaska. The exact trajectory of the system is still
unknown, with some models keeping the trough north of the
Aleutians through Sunday morning and other models pushing it
south as early as Saturday.

Over Southcentral, easterly flow will persist into Friday
afternoon as ridging continues to build in from Western Canada
over mainland Alaska. This will help support the formation of
afternoon showers as easterly waves and increased instability
build up over the course of the week. Weaker troughing will
persist over the Gulf through the forecast period until the
upper level trough from the Aleutians enters the Gulf. Model
guidance is suggesting a compact shortwave low could form and
impact parts of the northern Gulf Friday afternoon and evening.
The low is expected to dissipate over the Gulf by Saturday, but
the exact location is still unknown. The upper-level trough from
the Aleutians entering the Gulf on Sunday will provide unsettled
weather for most of the Southcentral coast as it looks to linger
over the area going into next week.

-BS
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&&

.AVIATION...

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PANC...VFR conditions and light winds will persist through the TAF
period. Showers and lower ceilings associated with an upper level
short-wave crossing the western Copper River Basin this afternoon,
will advect southward toward Anchorage tonight. These showers will
be moving into a more unstable atmosphere, limiting the chance for
actual rainfall. However, there is higher confidence that ceilings
will gradually lower this evening through the overnight hours,
likely reaching low end VFR. If rain does survive, there could be
MVFR ceilings in the vicinity, most likely east Anchorage and the
Front Range Chugach. Increasing low level westerly flow during the
day Monday will push much of the moisture eastward, leading to
lifting ceilings for the terminal.

-CC/SB
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&&

$$