580
FXAK68 PAFC 081430
AFDAFC

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
530 AM AKST Wed Jan 8 2025

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 through 3/Today
through Friday night)...

Looking at the upper level pattern this morning, a weak cut-off
low anchors a trough over the Bering Sea. A broad ridge can be
found to the east over most of mainland AK. A short-wave trough
is tracking overtop of the ridge from Bristol Bay and the far
western Gulf, northeastward across southern AK. radar imagery
shows precipitation ahead of this short-wave is quite light, with
snow over the northern Susitna Valley and low elevation rain/high
elevation snow across the Cordova/Valdez area into the southern
Copper River Basin. Gusty southeasterly winds ahead of the short-
wave have maintained balmy temperatures overnight, especially in
Anchorage where temperatures remain in the 40s. Winds are starting
to die down as the short-wave moves overhead, with temperatures
dropping through the 30s for much of the remainder of
Southcentral.

Meanwhile, a highly amplified subtropical jet over the North
Pacific has led to development of a deep storm force low down
around 44N/155W, with an amplifying ridge out ahead of it from
the far east Pacific up toward the Gulf of AK. This is causing
the storm system to track northward toward the Gulf.

As the aforementioned short-wave exits Southcentral later today,
precipitation will diminish and surface flow will lighten and shift
from southerly to northerly as the Pacific storm approaches. With
somewhat cooler air aloft, surface temperatures will steadily fall
as the winds die down. By this evening, expect areas away from the
coast will all be at or below freezing, allowing any water on area
roadways to refreeze.

The expected impacts from this storm for coastal Southcentral,
Kodiak Island, and the Gulf waters are largely on track - with
widespread rain and gale to storm force winds over marine areas.
However, some complexities have arisen in the last few model runs.
A strong upper level jet will help drive the leading frontal
system and upper level short-wave well out ahead of the parent
low. Most model guidance now develops a separate low east of
Kodiak Island tonight into Thursday morning while the original
low weakens and takes a track toward the eastern Gulf. Based on
this idea, it now looks favorable for precipitation to spread
inland late tonight through early Thursday morning. Forecast
soundings show the wet-bulb temperature largely at zero or below
inland from the coastal mountains right as precipitation first
spreads inland. Thus, if the atmosphere were able to saturate,
snow would be favored. However, strengthening winds and marginally
warmer air will push inland Thursday morning, indicating some
potential for rain (or freezing rain). With the upper level short-
wave rapidly tracking inland, do think precipitation will be light
and of a short duration for most areas. Though with the newly
formed low in the western Gulf, it looks favorable for a deformation
band of heavier precipitation to set up somewhere over Cook Inlet
and the western Kenai Peninsula. Temperatures will be just a bit
warmer here, so suspect rain will be the predominant precipitation
type, unless it is heavy enough for the melting process to cool
the column and bring snow down to the surface. Model guidance
varies on the both the low location and deformation band location,
so confidence is low at this point and will continue to work on
fine tuning this in future forecast updates.

Ultimately, a trailing trough and overall progressive flow will
kick the remnants of this storm northeastward across Southcentral
Thursday night, with a shot of light precipitation for most of
the region. Precipitation-type will remain a challenge from about
Anchorage southward, with snow likely as you head to interior
Southcentral. The progressive flow will steer a low from the
Aleutians to Southwest AK Friday, with another low tracking out
of the Pacific toward the western Gulf Friday night. There is no
big change in airmass with these systems, so rain will continue to
prevail along the coast, with mixed p-types as you head away from
the coast and snow over the interior. In this dynamic pattern,
forecast confidence quickly drops with time, so stay tuned as
storm tracks could change and greatly affect precipitation type
and distribution.

-SEB

&&


.SHORT TERM FORECAST SOUTHWEST ALASKA/BERING SEA/ALEUTIANS (Days
1 through 3: Today through Friday night)...

A small, weak and vertically stacked low continues to spin in
place over the central Bering Sea this morning to the west of the
Pribilof Islands. This low is embedded within a larger scale
trough encompassing most of the Bering Sea region. A large field
of snow showers generated by cool air passing over the still
fairly warm sea surface near and southwest of the low is
continuing to affect parts of the Aleutians and Pribilofs this
morning. Out across Southwest, a shortwave trough that earlier
lifted into the region from the AKPen is now moving up into the
Lower Kuskokwim Valley this morning, with a few lingering
rain/snow showers and areas of mist/fog still drifting over parts
of the region in the wake of this feature. Otherwise, relatively
calm conditions with light winds are in place to start today for
most of the outlook area.

In terms of the forecast, the expectation remains for things to
become a bit more active with time as two separate and stronger
lows begin to impact parts of the area beginning later tonight
into Thursday. By this evening, a North Pacific low entering the
Gulf of Alaska will spread northeast winds as strong as high-end
gale force into waters between the northern AKPen and Kodiak
Island. It`s also looking increasingly likely for an area of
deformation to set up northwest of this low across Southwest
between a shortwave driving northwest across the Alaska/Aleutian
Range and a separate shortwave lifting up into the Southwest
coastline on Thursday. The best chance for precipitation will be
focused from parts of the Kuskokwim Delta down into Bristol Bay.
Low level temperatures look like they will only be marginally
favorable for snow, but an inch or two of wet snowfall
accumulation will be possible for spots that can stay cold enough
for all snow down to sea level before precipitation dissipates
Thursday afternoon.

Looking to the second system of interest, a separate North Pacific
low will push its occluded front into the Aleutian Chain on
Thursday. Guidance has trended stronger with both the low and the
frontal feature, and winds have been strengthened to reflect a
gale force front reaching the Aleutians and far southern Bering on
Thursday with this package. Temperatures close to sea level will
start out cold enough for all snow to fall as the front approaches
the central/eastern Aleutian Chain, but a transition to mostly
rain is expected by late Thursday morning into Thursday afternoon
as the front continues to progress northeast and as warmer air
moves in behind the boundary. From Thursday night into Friday, the
parent low will cross over into the southern Bering Sea, then
continue northeast towards the Kuskokwim Delta as it begins to
weaken. A corridor of strong west to southwest winds will follow
near and south of the low as it heads northeast, with Storm force
gusts potentially impacting the eastern Aleutians on Friday
morning, depending on the exact low track and intensity.

Confidence for timing and strength of winds deteriorates as the
low approaches the Kuskokwim Delta, with a large spread in the
strength of an onshore push of winds that could reach the
Kuskokwim Delta on Friday evening. Even with this uncertainty, it
still looks likely for another round of snow changing to rain is
likely for much of Southwest as the low and front arrive from
Friday into Friday night.

-AS

&&


.LONG TERM FORECAST (Days 4 through 7: Saturday through Tuesday)...

A very active weather pattern will continue for much of southern
Alaska through the weekend into early next week. The longwave
pattern features a strong upper level low dominating much of the
Bering Sea and western mainland Alaska and a steep ridge of high
pressure along the Canadian Coast and Eastern Alaska. On Saturday,
heavy precipitation along the Southcentral coast continues as a
shortwave trough and associated surface low push inland.

By Saturday night, confidence is moderate to high on a strong
North Pacific low and its associated front traversing northward
across the Alaskan Peninsula into Bristol Bay and Southwest
Alaska. This pattern will bring unseasonable warmer temperatures
and mixed precipitation along the coastlines near the surface and
has the potential for heavy snow accumulations in the higher
elevations. Strong winds will also accompany this system across
Kodiak Island, the Alaska Peninsula, and the Bristol Bay and
Southcentral Alaska coastlines, although timing and intensity will
still depend on the the exact low track, where there is still
minor uncertainty. A new surface low may form off the Kenai
Peninsula early Monday morning, continuing and potentially
enhancing winds and precipitation along the coast through early
Monday afternoon.

-ME

&&

.AVIATION...

PANC...VFR conditions will persist. Northerly winds will develop
late this afternoon, then strengthen tonight as a deep low moves
into the Gulf. Winds could be gusty at times overnight through
early Thursday morning. It is looking increasingly likely that
there will be a brief period of light precipitation sometime
between 12Z and 18Z Thursday as an upper level short-wave tracks
inland. The persistent northerly flow will maintain dry conditions
near the surface, so ceilings will likely remain VFR. The
atmosphere will be marginally cooler than this morning, right on
the edge of rain and snow. Precipitation type will likely depend
on intensity, with lighter more intermittent precipitation
leading to rain and marginally heavier and steadier precipitation
leading to snow. Surface temperatures will be right around the
freezing mark, so freezing rain is also a possibility.

&&


$$