Gale Warning 737, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
500 PM AKST Mon Nov 27 2023

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 through 3/This
afternoon through Thursday afternoon)...

A longwave trough is in place over much of Alaska and the Bering
Sea, with several shortwave troughs embedded in the flow aloft.
These shortwaves will bring a continuation of active weather as
they move into Southcentral Alaska in the coming days. The primary
hazard to watch for will be heavy precipitation and the potential
for blowing snow through Turnagain Pass on Wednesday.

Overall, as can be seen today, precipitation type at the lower
levels remains a challenge. Many areas warmed much above freezing
today due to low-level southerly flow, leading to little in the
way of snow accumulation. With temperatures remaining right
around freezing through at least Thursday, there will continue to
be uncertainty with precipitation type at lower elevations.

For tonight, expect precipitation to become more sporadic as the
front weakens and showers move in behind it. More persistent
precipitation is on the way by Tuesday morning as the next
shortwave (and its attendant compact low) sweeps in from the
southwest. This will spell wet conditions for Kodiak Island,
Western Susitna Valley, Eastern Kenai Peninsula, and Prince
William Sound. With a colder airmass in place, this will be
mostly in the form of snow, with a mix of rain and snow likely for
areas along the coast near sea level. Southerly flow should keep
the remainder of Southcentral Alaska on the drier end due to
terrain blocking. Aside from some increases to precipitation
amounts for Prince William Sound, the biggest forecast update with
this system has been to increase winds due to the tightened
pressure gradient. Gusty winds are expected through Turnagain Arm
into South Anchorage, as well as from Knik Valley into Palmer and
across the Copper River area.

Stronger winds and heavier precipitation are on the way by
Wednesday as a deep North Pacific low tracks into the Gulf. Some
uncertainty remains with the position of the low center, but
confidence is high that winds will reach storm force in marine
areas along the coast and that heavy precipitation will affect
Eastern Kenai Peninsula. As mentioned previously, we are
monitoring the potential for heavy snow rates in Eastern Kenai
Peninsula (especially Turnagain Arm) on Wednesday morning, with
snow rates of 1 inch per hour possible. Winds will also be quite
gusty through Turnagain Pass through this time, but current
thinking is that warmer temperatures will lead to more of a wet,
heavy snow than a light, transportable kind; as such, blowing snow
is possible but not a major concern at this time. Overall, the
heaviest precipitation is expected in Eastern Kenai Peninsula,
with lighter precipitation expected in Prince William Sound. For
most other areas, downslope drying will keep precipitation fairly
limited.

-KC

&&

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

A broad, complex trough continues to slowly drift east over the
Bering Sea this afternoon as numerous smaller, embedded lows and
troughs rotate around the broad envelope of cyclonic flow. Two
notably potent lows producing winds up to gale force are now part
of this broader complex, one in weakening phase north of St
Matthew and another rapidly spinning up south of the eastern
Aleutian Chain. An army of convective snow showers is continuing
to affect much of the outlook area in between these two features
as cold air continues to stream east over the comparatively warm
sea surface.

Across the Southwest, the low currently forming south of the
Aleutians will soon become a key player in the forecast by later
tonight into Tuesday. This low will move very quickly northeast
across the AKPen later tonight, sending a quick round of rain and
higher elevation snow through along with winds briefly ramping up
to gale force on the Pacific side near and east of Sand Point. The
low will move swiftly north from there into Bristol Bay on Tuesday
morning, then up through the Lower Kuskokwim Valley before it
exits to the north by Tuesday evening. An intense but fairly brief
round of snow will follow this low north, while enough warm air
works in to the east of the center for a period of mixing or
changeover to rain across the southeastern two thirds of Bristol
Bay during the day on Wednesday. The heaviest snowfall will mostly
be focused over the Kilbucks and Kuskokwim Mountains, but as much
as 3 to 5 inches of accumulation will be possible for spots
including Togiak, Aniak and Sleetmute before the low moves off to
the north late on Tuesday. Conditions across Southwest will
become a bit calmer and cooler later in the week, although
additional light snow could affect eastern parts of the region as
another low moves into the Gulf on Wednesday.

Out across the Bering and Aleutians, snow showers and winds up to
low end small craft range will continue through Tuesday night as
the low currently north of Saint Matthew finishes making a
cyclonic loop back south almost all the way back to the Pribilofs
and finally dissipates early Wednesday. Meanwhile, a strong low
moving south of Kamchatka will push a gale force front into the
western and central Aleutians from late Tuesday night into
Wednesday. A warmer air mass with mainly rain will advance with
the front as it lifts north and as easterly gale force winds flip
to southwesterly behind the front along the Aleutian Chain on
Wednesday. The parent low will approach the far southwest corner
of the Bering late Wednesday night into early Thursday, pushing a
core of winds up to storm force and seas up to 40 ft into waters
south of the far western Aleutians through Thursday. A new low
will likely form along the front near the southern end of the
AKPen on Thursday as well, helping to focus continued periods of
mainly rain near Sand Point and Cold Bay.

AS

&&

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

The long-term forecast period begins Friday morning with fair
model agreement depicting a broad upper-level trough stretched
across the Bering Sea into the Gulf of Alaska, creating several
surface low pressure centers in the southeastern Bering and
northwestern Gulf. These lows will draw westerly gales across the
Aleutian Chain and easterly gales across the northern Gulf coast
into Prince William Sound. Generally a showery, wet pattern will
be in place across all of Southern Alaska, with areas such as the
lower Kuskokwim Valley, and Copper River Basin seeing relatively
less precipitation than surrounding regions. Looking into Saturday
model uncertainty increases, with some solutions keeping a low
pressure center spinning near Bristol Bay, while other solutions
retreat the low to the Western Bering. These discrepancies lead to
a difficult forecast as to the behavior of the Bering early next
weekend. By Sunday and Monday, model disagreements become severe
with some solutions keeping a low in the Southern Bering and
granting Southcentral a reprieve in rain and winds. While other
solutions spin up a new low pressure center in the northern Gulf
of Alaska coast that would bring another strong shot of
precipitation and strong winds to the Southcentral coastline,
while keeping the Bering relatively benign. Overall, a wet pattern
for the Aleutians and Southcentral regions, and looking colder
and drier from mid to late week for Southwest Alaska.

CL

&&

.AVIATION...

PANC...Gusty south winds around 15kt with gusts to 25kt will
continue through the evening and will diminish Tuesday morning.
CIGS and visibility this evening will remain predominately VFR,
but CIGS will become mainly MVFR after midnight and remain mainly
MVFR through Tuesday morning. Brief IFR CIGS are possible this
evening through Tuesday morning as scattered rain and snow
showers pass over the terminal.

CC

&&