Gale Warning 717, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
802 PM AKST Mon Nov 20 2023

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

Early tonight, strong winds will linger as cold air originating
from the Copper River Basin continues to pour out through the
Matanuska Valley and Thompson Pass, leading to a ground blizzard
in both locations. The peak of the event is still expected this
evening, but by midnight, winds and associated blowing snow is
expected to ease. Even so, transportable snow remains a concern
for Thompson Pass, with the potential for lofted snow with
moderate-strong winds. As such, Blizzard warnings remain in
effect for the Matanuska Valley and Thompson Pass through 6am
Tuesday and 9pm this evening respectively. Conditions overnight
will grow cold, however expected to not be as severely cold due to
a low in the Gulf of Alaska moving northward, pushing some upper-
level clouds across the area. These clouds will act as a sort of
thermal insulator, keeping areas such as the Copper River Basin
from reaching as cold of temperatures as last night. Copper River
Basin overnight low temperatures will likely stay around -10
degrees F, while Anchorage, Mat-Su, and Western Kenai will reach
the mid 10's F. A trend towards relatively warmer temperatures is
expected to continue through into Wednesday and beyond as the low
in the Gulf brings a round of warm, moist air into Southcentral.

Through Tuesday, the low aims to set near Prince William Sound,
with some model disagreement on exactly where. Periods of light
snow will persist throughout the day. For Tuesday night the
remnants of the surface low and an increasingly organized upper
short-wave trough will track inland, bringing potential for some
light snow in Anchorage and inland to the Mat-Su. The big
limitation will be how dry the airmass is right now. Thus, if it
does snow, accumulation will likely be very little.

Additionally, a frontal boundary swinging in from the southwest,
will cross Kodiak Island Wednesday morning, reaching and
augmenting the low pressure in Prince William Sound later
Wednesday afternoon. This front will bring steady and heavier
precipitation to the Prince William Sound and Eastern Kenai
Peninsula Wednesday through Thursday. Warmer air will accompany
this front northward, leading to a transition from snow to rain
Wednesday night through Thursday for all but the far interior
areas of Southcentral.

CL/SB

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 through 3: This
afternoon through Thursday afternoon)...

Expect cold and mostly clear conditions to persist across much of
Southwest Alaska through Tuesday. Most areas should see slightly
colder temperatures tonight than were experienced last night,
except for the Alaska Peninsula. Parts of Lower Kuskokwim Valley
and interior Bristol Bay could also see their temperatures
moderated by the bank of low stratus currently in the area, so
temperatures may not drop as low as they did this morning.

The bigger story will be the arrival of a front on Wednesday,
bringing precipitation type concerns. Given the current cold
spell, incoming warm air and moisture with this front could bring
the potential for freezing rain. We're also examining the
potential for blowing snow in Bristol Bay with the initial arrival
of the front. Overall, much uncertainty remains as guidance
continues to struggle with the timing of the front and the
positioning of its parent low near the Central Aleutians. However,
with precipitation looking to be a bit more spotty along this
occluded front, there should be a lower chance of major ice
accumulations. Stay tuned as we update and refine the forecast.

KC

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 through 3: This
afternoon through Thursday afternoon)...

Key Message: After a break tonight, windy and wet conditions
return on Tuesday/Wednesday and persist through Thursday.

The Bering Sea and Aleutian Islands will get a small reprieve
tonight as the current low rapidly weakens and exits north into
Russia. Its associated front, currently located near the Pribilof
Islands and Eastern Aleutians, will also weaken through tonight.
All in all, this will bring weakening winds across the region,
with precipitation along the front gradually tapering off this
evening.

By early Tuesday morning, a strong North Pacific low begins to
impact the Aleutian Chain. This low continues to be rather vexing;
model guidance differs appreciably with the track of the low,
even spinning up multiple low centers. Overall forecast confidence
remains decent with the strength/magnitude of weather elements,
though the timing and placement of the strongest winds or highest
precipitation amounts could shift as guidance attempts to hone in
on this low. For now, expect precipitation to reach the Western
Aleutians by early Tuesday morning as the front moves in. The
Central and Eastern Aleutians will see precipitation by late
Tuesday and Wednesday, respectively, as the front sweeps in ahead
of the occluding low. With the low remaining nearly stationary
south of the Central/Eastern Aleutians as it occludes, expect
precipitation to persist through at least Thursday afternoon.
Precipitation rates will be heaviest around onset, with precipitation
becoming more showery by Thursday. As for winds, expect up to
high-end gales on the backside of the low and along its front.

KC

&&

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

The low sitting near the central and eastern Aleutians midweek
will begin to slowly trek east and weaken with its front pushing
through Southcentral under southerly flow. Warmer air and multiple
waves of precipitation can be expected through the end of the
week into next week. Temperatures will trend warmer, with Friday
being into the 40s for the Aleutians, the Alaska Peninsula, and
Bristol Bay and into the 30s for the rest of Southwest. Similarly,
temperatures will also trend warmer for Southcentral with areas
near the coast well into the 40s with 30s elsewhere.

Along with the frontal passage, should any precipitation form
over the Kuskokwim Valley, cool enough air remaining at the
surface could lead to mixed precipitation type forecast
challenges. Many locations across Southcentral that have been cool
and snowy lately, will likely see rainfall for the Thanksgiving
Holiday weekend. Copper River Basin will likely stay at or below
freezing. Southeast flow through the Gulf could downslope the
western Kenai Peninsula, Anchorage, and Mat-Su. While that could
mean less potential for precipitation, it could also mean warmer
than forecasted temperatures if that warm air mixes to the
surface. Precipitation type could be a challenge to forecast later
in the week, especially for areas of transiting temperatures
further inland and at higher elevations but enough warm air should
be established by the end of the week for a clearer delineation
of rain and snow.

A low moving north into the western Bering Sea is indicating at
least storm force winds with some hints of hurricane strength
potential Saturday. The front will then track east across the
Aleutians over the weekend, replacing the weakening low that was
over the eastern Aleutians from midweek. The progressive track
will generally be along the same trajectory that will continue on
a path right into the Gulf. For the early part of next week, QPF
will depend on the timing of the front into Southwest Alaska and
the position of the low moving into the Gulf. The phasing of these
two features Monday night could bring ample moisture to the
Susitna Valley.

rux

&&

.AVIATION...

PANC...VFR conditions will prevail until Tuesday evening when
there is a chance of MVFR conditions in light snow. Forecast
confidence in the occurrence of snow is low. Meanwhile, gusty
northerly winds have diminished. Some fluctuations in the
orientation of the pressure gradient could bring a short period
of northerly gusts overnight, but most likely winds will remain
less than 10 kt.

SB

&&

Preliminary Local Storm Report
National Weather Service Anchorage AK
1228 AM AKST Tue Nov 21 2023

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

0209 PM     Non-Tstm Wnd Gst Wasilla                 61.57N 149.54W
11/20/2023  M69 MPH          Matanuska-Susitna  AK   Mesonet

            Strongest wind gust recorded at Wasilla AWOS
            station this afternoon.

&&

Preliminary Local Storm Report
National Weather Service Anchorage AK
1232 AM AKST Tue Nov 21 2023

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

0545 PM     Non-Tstm Wnd Gst 4 mi SE Wasilla         61.56N 149.33W
11/20/2023  M68 MPH          Matanuska-Susitna  AK   Mesonet

            Strongest gust recorded at a CWOP station
            this afternoon.

&&

Preliminary Local Storm Report
National Weather Service Anchorage AK
1237 AM AKST Tue Nov 21 2023

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

1253 PM     Non-Tstm Wnd Gst Palmer                  61.60N 149.09W
11/20/2023  M70 MPH          Matanuska-Susitna  AK   Mesonet

            Strongest gust recorded at the Palmer ASOS
            during the afternoon. Winds were also
            causing significant blowing and drifting
            snow.

&&

Preliminary Local Storm Report
National Weather Service Anchorage AK
1243 AM AKST Tue Nov 21 2023

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

0910 AM     Non-Tstm Wnd Gst Thompson Pass           61.13N 145.73W
11/20/2023  M89 MPH          Chugach            AK   Mesonet

            Strongest wind gust recorded at the RWIS/DOT
            observation site this morning.

&&