Gale Warning 132, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
601 AM AKST Thu Feb 9 2023

.ANALYSIS AND UPPER LEVELS...

A negatively tilted trough extending from the Alaska Peninsula
across the Kenai Peninsula and northern Gulf is slowly lifting to
the Copper River Basin. An upper level wave within the trough is
moving north from the Gulf to Southcentral, leading scattered snow
showers mainly along Prince William Sound. The snow is slowly
coming to an end for the low-lying region, but lingering across
the higher elevations. A ridge of high pressure meanwhile is
building from the west, allowing colder temperatures, partial
clearing skies, and drier air to move in over Southcentral. Low
stratus and fog trapped underneath the ridge has developed over
the Susitna Valley to Anchorage Bowl and into the western Kenai
Peninsula. For Southwest Alaska, a small band of snow showers are
moving east across Bristol Bay, while clear skies and strong
radiational cooling elsewhere allowed overnight temperatures to
drop into the single negative digits. Out west, a strong North
Pacific low is tracking near and just south of the Aleutian Chain.

&&

.MODEL DISCUSSION...

Model guidance is in good agreement with the placement and
intensity of synoptic scale features at both the surface and in
the upper levels. The main challenge with the aforementioned
North Pacific low continues to be winds and precipitation type
along the Alaska Peninsula and Aleutians. By the end of the week,
an active weather pattern will get underway as the attendant
front pushes eastward across Southwest and Southcentral Alaska.

&&

.AVIATION...
PANC...Low stratus and fog has formed over Anchorage Bowl and
will persist through early this afternoon with MVFR/IFR
ceiling/visibility. Conditions are expected to improve around 21z
with VFR and light winds for the rest of today.

&&

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

A mid-level ridge extending from Kodiak Island to the Susitna
Valley this morning continues to keep lingering low-level moisture
in the wake of yesterday's trough over Cook Inlet and the
Anchorage Bowl. The challenge today will be how long these clouds,
and any developing fog and flurries, remain in place prior to the
next weather system moving in from the western Gulf for the
latter half of Friday. The aforementioned ridge is expected to
slow drift eastward over the Kenai Peninsula through around noon
today before an upper-level shortwave moves in from the west,
allowing the ridge axis to move over the northern Gulf. At this
point, colder air advecting over Cook Inlet, along with a stronger
westerly flow, should mix out the antecedent airmass and erode
any linger cloud cover by Friday evening.

Farther east, clouds and flurries also linger across the Copper
River Basin. This is due to a southerly flow and weak moisture
advection across the area due to a trough near the entrance to
Prince William Sound. Again, clouds and flurries should dissipate
later today as the trough weakens as upstream shortwave moves
through the region. With clouds on the decrease tonight,
temperatures should drop below normal across much of Southcentral.
The warmest temperatures will remain along the immediate coast
where offshore winds will remain gusty through Friday evening.

Active weather returns to Kodiak Island for Friday morning as an
occluded front moves to the western Gulf. Snow and blowing snow is
expected for Kodiak City early Friday morning, with up to 5 inches
of snow possible, before temperatures warm with an onshore flow
and the snow changes to rain. This front pushes to the northern
Gulf for late Friday, reaching the Southcentral coast by Saturday
morning. Snow will overspread the the eastern Kenai by Friday
afternoon and Prince William Sound by Friday evening.
Southeasterly gap winds will increase Friday afternoon through
Turnagain Arm, including Portage Valley and parts of Turnagain
Pass. Easterly winds will also be on the increase for Whittier.
Areas of blowing snow area also likely for these locations.

Winds will also increase across the Matanuska Valley by Friday
afternoon in advance of the front. Periods of blowing snow area
possible from Palmer to Wasilla through early Saturday morning.

The front finally lifts onshore Saturday before stalling and
weakening with snow mixing with or changing entirely to rain for
coastal locations from Seward to Cordova. Precipitation lingers
along the coast into Sunday with the potential for some snow to
overspread Cook Inlet and the Mat-Su Valleys late Saturday.

&&

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

Quiet weather this morning gives way to more active and
potentially hazardous weather by the afternoon. For today, a band
of light snow will continue to move over parts of the Lower
Kuskokwim Valley and Bristol Bay as it exits towards the Western
Alaska Range. Further west, clouds extending from the Bering Sea
and west towards the Kuskokwim Mountains have kept conditions a
bit warmer for the morning, with air temperatures dipping
remaining in the single digit negatives or higher for most areas.
Colder air temperatures return tonight as skies clear, with a
Wind Chill Advisory in effect as apparent temperatures drops into
the high -30s and low -40s.

For Bristol Bay and south, the main story is a 956 mb low that
will move north towards Adak and begin tracking along the Aleutian
Chain later this morning. Its front pushes across the Alaska
Peninsula by early afternoon, bringing moderate to heavy
precipitation and strong winds. The forecast looks largely on
track, with the potential for some visibility reductions due to
blowing snow over the Alaska Peninsula before snow transitions to
rain. Bigger visibility reductions are expected for Bristol Bay,
with a Winter Weather Advisory in effect from Dillingham and west
due to the potential for visibilities to one-half mile or less in
blowing snow. Overall, about 6-10 inches of steady light snow are
expected from early Friday morning through Saturday morning along
the Kuskokwim Mountains, though total amounts could fluctuate as
we continue to refine the forecast.

&&

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

The forecast remains largely on track, with a High Wind Warning in
effect for the Central Aleutians and a Blizzard Warning in effect
for the Pribilof Islands as a 956 mb low and its front move along
the Aleutian Chain and Southern Bering. The biggest change with
this forecast package was to quicken the transition from snow to
rain or rain/snow mix for the Central Aleutians. With temperatures
looking a bit warmer than initially expected, blowing snow has
become less of a concern. As for the Blizzard Warning, newer
guidance is keeping precipitation a little further south. While
winds will still remain fairly strong, blowing snow may not be as
bad or last as long for St. Paul Island. Further north near the
sea ice edge, cold air temperatures in conjunction with brisk
winds will lead to heavy freezing spray and extreme heavy freezing
spray from late this afternoon through tonight.

&&

.LONG TERM FORECAST (Days 4 through 7: Sunday through Wednesday)...

A progressive pattern will amplify by mid-week, pushing a series
of storm force lows and fronts through the forecast area. Run to
run consistency is above average, with model solutions remaining
similar to yesterday, lending confidence to the long term
forecast. Sunday morning, a low entering the Gulf of Alaska will
push a front to the north Gulf coast, bringing a round of heavy
precipitation. The track of the low will serve to keep much of
the inland areas dry, with little warm air expected to work its
way into the mainland. This will keep most precipitation snow,
though there is a chance of rain at low elevations along the
immediate coast.

Model guidance continues to indicate that a weak front on the
back side of the low will bring light snow to Southwest Alaska,
with some potential to move into Southcentral as early as Sunday
evening. This is one of the most uncertain aspects of the long
term forecast, though snow accumulations appear to be limited to
a few inches at most. Uncertainty stems from the potential for a
deep cut-off low to be centered over Western Alaska on Sunday,
which would aid in providing lift and instability for
precipitation. It would also correspond to much lower
temperatures for Southwest Alaska as well, with the EC and GEM
suggesting 850 mb temperatures as low as -30C in tandem with the
cut-off low. However, the weaker depiction of this feature in GFS
suggests uncertainty in how cold temperatures will get.
Regardless, cold air will help to drive strong winds out of gaps
on the south side of the Alaska Peninsula and along the western
Gulf. These winds are likely to gust to storm force, and in
localized areas storm force winds may be sustained. Gap winds
diminish Monday night as the low in the Gulf weakens. Shower
activity decreases along the north Gulf coast as well, and the
decaying front leaves much of the southern mainland dry by Monday
night.

At the same time, a strong storm force, or potentially hurricane
force, low in the North Pacific passes south of the Aleutian
Islands. The low track has nudged a bit closer to the island chain
with a more northerly model consensus compared to yesterday. Its
front pushes across the central and eastern Aleutians on Monday,
bringing easterly winds as strong as storm force. This also looks
to be another potential significant snowfall event for the
islands, with more cold air in place over the Bering Sea ahead of
the low. Snow moves up along the Alaska Peninsula into Bristol Bay
and over Kodiak Island on Tuesday. There will be some potential
for the low to track into the southern Gulf, allowing its front to
move up along the north Gulf coast bringing another round of
precipitation, with only a limited amount spreading inland. Then,
a strong front off another deep low near the Kamchatka Peninsula
brings a strong southerly push of warmer air late on Tuesday. This
should be enough for precipitation to switch over to rain as the
front sweeps from the western Aleutians to the central Aleutians
through Wednesday.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...Blizzard Warning 195
		 High Wind Warning 187
		 Winter Weather Advisory 125, 161, 171
		 Wind Chill Advisory 155
MARINE...Heavy Freezing Spray Warning: 129, 130, 140
		 Storm Warning: 130, 170, 172-176, 179, 413, 414
	Gale Warning: 119, 120, 131, 132, 138, 139, 150, 155, 160, 165,
	171, 177, 180, 351-352, 411-412.
FIRE WEATHER...NONE.

&&

SYNOPSIS AND MODEL DISCUSSION...MF
SOUTHCENTRAL ALASKA...TM
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...KC
LONG TERM...CQ