Winter Weather Advisory 66, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
427 PM AKST Tue Dec 7 2021

.ANALYSIS AND UPPER LEVELS...

An upper level trough extends along an axis from north to south
over the Alaska-Yukon border. At the base of this trough is a
decaying low over the northern Gulf that is gradually drifting
toward the southeast. Residual snow showers continue across
Southcentral, and Kodiak Island saw impressive westerly winds
earlier today with peak gusts reaching 62 knots thanks to a strong
pressure gradient. Conditions across both of these areas have
improved as the low is gradually moving away from the coast.
Farther west, a 170 kt jet streak at 300 mb over the western
Bering is helping to push an upper level shortwave over Kamchatka
into the Bering. Westerly zonal flow continues across the Bering
as this jet streak continues to push eastward. Clouds and
widespread showers will continue across the Bering and Aleutian
Chain.

&&

.MODEL DISCUSSION...

Model solutions are in great synoptic agreement through the short
term and depict the Gulf low tracking toward the southeast by
tonight. There is also consistency in the arrival of a fast-moving,
but relatively strong front to the Southwest coast overnight. Key
upper level features associated with this front are in agreement
across models as well. By Wednesday night into Thursday, the
models are struggling to resolve some features with another low
tracking across the Bering from west to east. While the upper
level low position remains consistent with a track over the Alaska
Peninsula and into the Gulf by Thursday morning, there are some
discrepancies with the timing of the surface low. Right now, the
NAM/Canadian solution is slightly stronger, and suggests stronger
northwesterly winds across the Alaska Peninsula and Kodiak Island
on Thursday. However, earlier in time on Wednesday night, the GFS
presents a much more compact low, which would support strong winds
over the southern Bering and central Aleutians. Overall, there is
moderate confidence in the forecast and a blended approach was
used for the short term.

&&

.AVIATION...

PANC...Any remaining snow showers should clear out and move east
this evening, allowing conditions to improve to VFR. Light
northerly winds will persist through the TAF period.

&&.

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

Snow showers have begun tapering off this afternoon in most areas
across Southcentral. Radar shows residual, rather persistent band
of snow showers lingering in central Kenai, east of Soldotna and
extending up into the Mat-Valley. Anchorage to Palmer, including
Wasilla, will likely continue to see these light, intermittent
snow showers throughout the evening, clearing out by tonight.
Gusty winds continue through the night tonight for the usual
well traveled marine areas, including Passage Canal, Resurrection
Bay, and Valdez Narrows/Arm, and will begin diminishing through
the early morning hours on Wednesday. Additionally, Kodiak City is
seeing increased wind speeds this afternoon that will continue
through this evening, diminishing tonight, before picking up again
tomorrow afternoon. Cold air is building back in behind the low
that has now moved into the the eastern Gulf, and is gradually
dropping temperatures across Southcentral.

Another low lifts into the Gulf on Thursday, its front pushes the
North Gulf Coast, creating increasingly gusty winds leading into
Prince William Sound. The GFS is hinting at the possible development
of storm force winds within the Barrier Jet Thursday night, while
the other models leave high end gale force winds. This will
continue to be closely monitored for any potential changes. Warmer
air accompanies the incoming front, however, the warming does not
look to be as significant as the previous system, but will bring
temperatures around Cordova and Whittier to balance on the cusp
of freezing Thursday and Friday. That being said, it is also set
up to bring heavy snowfall to both areas as well. It is very
likely we will see a similar pattern as the most recent system,
with precipitation rates being high enough to permit snowfall even
with temperatures at or just above freezing. Models are in decent
agreement on low placement as it tracks towards PWS. The NAM is
moving a bit faster than the GFS and EC and takes the low into PWS
while the GFS/EC stays just south by Friday. This will inevitably
alter snow amounts and areas of heaviest precipitation depending
on where the low ends up. Be on the lookout for any incoming
winter weather products, most notably along the North Gulf Coast
and Prince William Sound regions.

&&

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

An active pattern will continue across Southwest Alaska over the
next couple of days. First there will be a frontal system moving
through the area this evening and tonight and will bring a quick
1-3" of snow with locally higher amounts in the Ahklun and Kilbuck
Mountains. Strong westerly winds will accompany this snow
(especially across the Kuskokwim Delta Coast) and will allow for
reduced visibility at times. A Winter Weather Advisory remains in
effect for the Kuskokwim Delta Coast from 9pm AKST this evening
through 12pm AKST Wednesday due to areas of blowing snow reducing
visibility to one half mile at times.

A strong low pressure system will move across the area Wednesday
night through Thursday night. This storm system is likely to bring
blizzard conditions to much of the northern Alaska Peninsula and
Bristol Bay. The highest snowfall totals are expected to range
between 6-12" across Bristol Bay with lower amounts across the
Kuskokwim Delta and lower Kuskokwim Valley. Blizzard conditions
are expected as 30-40 mph sustained winds with 50-60 mph gusts are
expected to accompany the heavy snow at times and reduce
visibility to less than a quarter mile at times. A Blizzard Watch
remains in effect for Bristol Bay from late Wednesday night
through late Thursday night. Blizzard conditions will gradually
taper off on Friday, except for areas along the northern Alaska
Peninsula where winds will remain northwesterly at 35-45 mph with
snow showers.

&&

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

A very active pattern is expected for the Bering/Aleutians during
this forecast period. A strong storm system is expected to move
across the southern Bering Sea and into Bristol Bay from Wednesday
morning through Thursday night. This storm will produce a
widespread area of storm force winds with hurricane force gusts.
The strongest winds will be along the eastern Aleutians and Alaska
Peninsula as these areas will experience the back side of this low
where strong cold air advection will mix down stronger winds aloft
to the surface. The Central Aleutians also has a chance of
experiencing hurricane force gusts, though confidence in this area
is lower compared to the Eastern Aleutians and southern Alaska
Peninsula. A High Wind Watch has been issued for the Central
Aleutians from Wednesday afternoon through Wednesday evening. A
High Wind Watch has been issued for the Eastern Aleutians from
Wednesday evening through Thursday morning. A High Wind Watch has
been issued for the southern Alaska Peninsula from Wednesday
evening through Thursday afternoon. High seas will also accompany
this storm system with wave heights of over 20ft expected.

&&

.MARINE (Days 3 through 5: Fri thru Sun)...

Aleutians/Bering... Confidence is good for upper level support
moving South over the Bering. This brings widespread gales over
the Aleutians and Bering, with local storm force winds across the
Aleutians and Alaska Peninsula for Friday, diminishing. Seas to 25
feet over the Bering Fri, subsiding, and to 22 feet on the
Pacific side of the Aleutians and Alaska Peninsula through Sunday.
A new North Pacific low and front moves across the Western
Aleutians and Bering on Sunday. Widespread high-end gales and seas
building to 20 feet expected for Sunday.

Gulf of Alaska... A well-developed Northern Gulf low moves to the
Southeast Gulf for Sunday. Widespread high-end gales persist
through Sunday over the Gulf. Areas of storm force outflow winds
along the Pacific side of the Alaska Peninsula, Shelikof Strait
and Barren Islands for Saturday and Sunday. Seas to 25 feet across
the Northern Gulf, subsiding, and building to 30 feet over the
Southern Gulf by Sunday.

&&

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

A broad trough is forecast to be in place over Southcentral
during the weekend with active rain and snow showers over the
Northern Gulf and enhanced easterly winds along the coast. West of
the trough several smaller upper-level disturbances will be
digging southward over the eastern Bering within highly a
amplified flow. This should effectively help to amplify the trough
over the Gulf while also pushing the trough further east. At the
same time a tightened pressure gradient over the Bering will
contribute to very strong northerly winds across the Aleutians and
Alaska Peninsula with storm force gusts and heavy freezing spray
a good possibility late Saturday into Sunday. Aiding in the the
tightening of the pressure gradient will be a strengthening ridge
of high pressure south of Kamchatka. This ridge is expected to
slide east and overspread the southern Bering and Alaska Peninsula
by Monday. Even further behind, the next upper low will quickly
bring another barrage of smaller disturbances northeastward out of
the North Pacific and across the Aleutians with several rounds of
rain, snow, and elevated winds Monday into Tuesday. High pressure
from the weekend will eventually overspread the Gulf early next
week with a brief period of calmer conditions forecast on Monday.
This calm should be short-lived, however, with the first of
several disturbances to impact the Aleutians on Monday finally
reaching the Gulf by Tuesday as a negatively tilted trough. A
strong front associated with the trough will bring widespread
precipitation over Kodiak Island and the Kenai Peninsula. Lastly,
a new broad low pressure center is forecast to amplify over the
Bering Monday into Tuesday. Snow showers and enhanced winds and
heavy freezing spray will be a good bet for the Bristol Bay area
and the Kuskokwim Delta next week.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...Blizzard Warning 141 195
		 Winter Storm Warning 131
		 Winter Weather Advisory 111 155
		 Winter Storm Watch 161
		 High Wind Watch 181 185 187

MARINE...Storm Warning 130 131 155 165 170-176 179 180
		 Gale Warning 119 120 125 129 132 136-139 150 160 177
					  178 180
		 Heavy Freezing Spray Warning 129 160 180 185

&&

SYNOPSIS AND MODEL DISCUSSION...KO
SOUTHCENTRAL ALASKA...KM
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...ED
MARINE/LONG TERM...MK/BL