Gale Warning 803, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
443 PM AKST Mon Dec 5 2022

.ANALYSIS AND UPPER LEVELS...

A broad area of low pressure is centered north of the Kamchatka
Peninsula with several shortwaves moving across the western and
central Bering and Aleutians. These features are producing small
areas of gales with rain and snow showers. A fairly strong front
is pushing across the eastern Bering and into Southwest Alaska.
This front is producing winds up to 35 to 45 knots across the
AKPen and coastal areas of the southwest. Rain was also reported
along the front across the Pribilofs, the AKPen, and the eastern
Aleutians with temperatures in the upper 30s to low 40s. Farther
east another front extending from Kodiak Island and northward
through the Kenai Peninsula and into Southcentral is making its
way eastward. This front is producing light snow across the Kenai
Peninsula northward towards Anchorage and the Mat-Su valleys.
Rain has been reported near this front at Kodiak City and around
Kachemak Bay with warmer temperatures near the coast. Finally,
the ridge that has been over the area has moved east near the
ALCAN border.

&&

.MODEL DISCUSSION...

Guidance is in good agreement with the large scale features,
however it continues to struggle with the front and triple point
low forming across the Gulf on Tuesday. Some models show the
strongest dynamics over the Gulf with a stronger surface low
near the central Gulf with only weak shortwaves moving inland.
While other models show a weaker low over the northern Gulf and
more dynamics moving inland. The main forecast challenge for
today will be the transition of sleet to all snow across the
Anchorage area, and the location of heavier snow bands and snow
amounts across Southcentral on Tuesday and Wednesday morning.

&&

.AVIATION...
PANC...IFR will lift to MVFR conditions this evening as snow will
taper off tonight with periods of flurries or light snow through
tomorrow morning with accumulations of a half inch or less
overnight. Snow is expected to increase in intensity tomorrow
afternoon, so expect IFR conditions for most of the day tomorrow.
Otherwise light northerly winds today becoming variable tonight.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 and 2:
Monday afternoon through Wednesday afternoon)...

The first round of snowfall for Southcentral has moved through
today. While light snowfall will continue through the evening, it
should lighten up across most locations, and even a brief break
can be expected during the overnight hours tonight. Additional
snowfall is expected tomorrow as an upper level trough arrives to
Southcentral and continues to "dig" south and east, spreading snow
from west to east. While the models have shown better agreement
at 500 mb with the synoptic features, there is still a lot of
uncertainty with regard to the surface features with this event.
Thus, there is lower confidence in expected snowfall amounts,
particularly for the Tuesday into Wednesday timeframe.
Additionally, one complicating factor is the chance for a
deformation band to setup over Southcentral sometime Tuesday
evening. If this occurs, this feature would produce localized
heavier bursts of snow over a short period of time. Current
thinking is that there is a good chance for this feature to set
up over the Cook Inlet region, possibly extending from the
northern Kenai Peninsula through southern Susitna Valley, however
nailing down the exact location of where this heavier band will
setup is quite difficult. Meanwhile, Gulf coastal locations will
likely see a rain/snow mix on Tuesday, or mostly rain as
temperatures will remain warmer for Tuesday in those locations.

As far as the duration of this event, it does appear that
snowfall will linger a bit longer than previously anticipated,
with models now suggesting lingering snow showers through
Wednesday afternoon. There is higher confidence of this occurring
at higher elevations where upsloping is favorable.

As this upper level trough tracks eastward late Wednesday night,
expect a return of cold air and gusty northerly winds for the end
of the workweek.

&&

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

The front stretching from a low near the Gulf of Anadyr is
continuing to move east along the Alaska Peninsula and inland
Southwest. Cold air is expected to advect from the west behind the
front and temperatures will trend cooler over the next few days.
Another weak shortwave will follow closely behind tomorrow morning
bring another wave of precipitation and gusty winds along the
coast and into Bristol Bay. Winds and precipitation will decrease
for Wednesday as a ridge builds from the west and flow will
predominantly be from the northwest.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 through 3)...

Westerly flow across the Bering Sea and Aleutians will continue
through Tuesday night. Low end gale force winds were observed with
the scatterometer pass this afternoon. With a low near the Gulf
of Anadyr and a front through Southwest Alaska, much of the Bering
Sea and Aleutians are under more conditionally unstable airmass
with cumulus clouds and multiple shortwaves moving from west to
east. Winds, however, are expected to gradually decrease through
Tuesday night. A flattened ridge is expected to build over the
Aleutians Tuesday and spread eastward through Wednesday when a
North Pacific low moves toward the Aleutians. The low progression
appears to weaken as it moves northeast and the gale force,
easterly winds appear to be either be less likely or delayed.
There is some east-west disagreement in the models that could
affect where the precipitation, QPF, and strongest winds will
occur.

&&

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

Long term model guidance continues to show significant
discrepancies with placement of key synoptic features over the
weekend. Ensembles are initially in somewhat good agreement to
start the day 4 period on Friday. Weak ridge of high pressure will
be making its way into Southwest Alaska from the eastern Bering
while a trough of low pressure over the eastern Gulf of Alaska
slowly exits the region to the southeast. Thus average to above
average confidence exists in decreasing precipitation over
Southcentral along with decreasing temperatures over Southcentral
on Friday. This should also see any precipitation over the Bering
and Southwest also diminish on Friday with temperatures from the
Aleutians into Southwest remaining generally unchanged.

Saturday into Sunday is where confidence begins to drop off more
dramatically. The GFS ensemble brings a developing low across the
Aleutians, much further south than the EC, while amplifying a
ridge into Southeast Alaska. The EC ensemble paints a less
amplified pattern, with a weaker trough skirting the Aleutians and
a weaker ridge of high pressure over the Gulf of Alaska. The
implications being much stronger northerly flow with the GFS and
the potential for widespread gales through the Aleutians, Alaska
Peninsula and into the Gulf of Alaska by Sunday. The EC would
promote milder winds over the Aleutians on Saturday, but does
agree on enhanced drainage winds into the Gulf of Alaska on Sunday
as low pressure begins to build offshore of Southeast Alaska.
Ultimately, both ensembles have a more amplified trough building
into the eastern Gulf of Alaska by Monday with high pressure
ridging into the Central Aleutians.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...Flood Advisory 155.
MARINE...Gale 130 131 132 150-165 173 175 177-179 185.
FIRE WEATHER...NONE.

&&

SYNOPSIS AND MODEL DISCUSSION...RC
SOUTHCENTRAL ALASKA...KO
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...VR
LONG TERM...BL