Small Craft Advisory 35, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
441 PM AKST Thu Jan 13 2022

.ANALYSIS AND UPPER LEVELS...

A 965 mb surface low situated south of the AKPen continues to lift
northeast toward Kodiak Island. This low is tapping into a deep
moisture feed originating near the Hawaiian Islands, where total
precipitable water values still exceed 150% or more of normal.
This stream of moisture is lifting across the eastern Gulf then
bending northwestward into the Southcentral coast, aided by a
strong southeasterly flow out ahead of front draped across the
central Gulf. The core of the moisture and strong southeasterly
winds is aimed at the eastern Kenai Peninsula and Western Prince
William Sound. Snow that fell this morning for locations like
Seward and Portage have since changed over to rain this afternoon.
Snow has also changed to rain for Kodiak City with the passage of
the front. Gusty southeasterly gap winds also continue this
afternoon, mainly through Turnagain Arm, where occasional gusts
over 60 mph have been reported.

The vast majority of the precipitation is confined to the coast
and along the upslope side of the Kenai and Chugach Ranges due to
the strong southeasterly, cross-barrier flow. However, as weak
upper-level waves lifts onshore ahead of the surface front,
pockets of precipitation, flurries mainly, are popping up from
Kenai and Soldotna north to Anchorage. With the low southeast of
Cook Inlet, locations in the Mat-Su Valleys south along Cook Inlet
have also seen an increase in northerly winds.

Farther west, precipitation and gusty winds are also occurring
around Bristol Bay this afternoon. Light snow has been falling
from Koliganek to Dillingham with more of a wintry mix from Port
Heiden south across the AKPen.

For the Bering and Aleutians, a northerly to northeasterly flow
persists, with occasional snow showers due to instability
generated from a cold airmass moving over warmer waters south of
the ice edge.
&&

.MODEL DISCUSSION...

Model guidance remains in good agreement out through Saturday
morning before beginning to diverge. Guidance remains consistent
with the evolution of the upper level features and surface
features with the current storm system moving northward through
the Gulf and into Southcentral through Friday. It is the next
shortwave originating over the Bering on Friday where the
discrepancies arise. While all show this feature gaining strength
and consolidating into an upper-level low as it moves east over
Southwest Alaska, it is how it evolves as it moves over
Southcentral or Gulf of Alaska by Saturday. The NAM and GEM have a
more northerly track with a surface low developing just off the
eastern Kenai Peninsula coast while the GFS has a more southerly
track with a surface low spinning up closer to Middleton Island.
The former would favor snow across the southern half of
Southcentral, including locations from Kenai to Palmer. The latter
would keep the bulk of the precipitation closer to the coast and
mainly from Prince William Sound east. Thus, forecast confidence
with this next potential system is below average.

Model guidance also remains in good agreement on another storm
force low moving into the Aleutian Island Chain/Bering Sea Friday
evening and through the weekend.
&&

.AVIATION...

PANC...VFR conditions are mostly expected throughout the TAF
package. However, occasional gusty northerly winds are expected
through late afternoon before diminishing through the evening and
overnight hours. Though, expect southeasterly winds around 2000 ft
causing wind shear over the terminal. Occasional flurries and/or
light snow with ceilings to MVFR are also possible through early
this evening. A southeasterly Turnagain Arm wind is expected to
bend over the terminal by mid-morning Friday as this the surface
low currently near Kodiak Island moves up Cook Inlet. Any
precipitation that tracks with the low could fall in the form of
rain as temperatures climb above freezing with the southeasterly
wind. Any rain that does fall, however, would be light in
intensity and short in duration.

&&

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

A beautifully wrapped up low is centered just south of Kodiak
Island and continues to lift northward this afternoon. The leading
frontal boundary has pushed inland over Southcentral, bringing
gusty easterly winds to the northern Gulf coast and rain to coastal
locations. Meanwhile, snow continues to fall at higher elevations.
As this low continues to track northward, gusty southeasterly
winds will continue through Turnagain Arm. Northerly winds are
expected to hold across the Cook Inlet until late this evening,
shielding the Anchorage Bowl from Turnagain Arm winds however by
Friday morning, winds are expected to bend into Anchorage.
Meanwhile higher elevations such as the Anchorage Hillside will
see gusty southeasterly winds beginning to increase as early as
this evening. As a result of the southeasterly flow, the western
Kenai Peninsula, Anchorage Bowl, and southern Mat-Su Valleys will
be downsloped and won't see much precipitation for Friday.

As the upper level trough associated with this low lifts inland
on Friday, precipitation will taper and winds will diminish by the
afternoon. Then all attention shifts to a weak surface low
spinning up over the northern Gulf tracking from east to west
Friday night into Prince William Sound. This surface low, in
combination with an approaching upper level low over Southwest
Alaska, has the potential to bring snow to much of Southcentral
on Saturday. Confidence remains low with this next system, as
model solutions struggle to resolve several key features and
timing, however the main ingredients are slowly coming together.
Please stay tuned as we continue to monitor the development of
this system.
&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Day 1 through 3: Tonight
through Sun)...

Precipitation has arrived for the Bristol Bay area with
temperatures already in the 30s. Iliamna has remained dry due to
downsloping through this afternoon. King Salmon had a brief snow
shower but also generally remained dry. There is still a chance
for precipitation to fill for those areas. Additionally, while the
majority of precipitation around the area has fallen as snow, the
possibility for a wintry mix including freezing rain cannot be
completely ruled out. High resolution models have a few hours
tonight that increase a warm nose temperature in the mid to lower
levels, including a wet bulb temperature just above freezing. By
Friday morning, enough cold air will return with generally
northerly flow to turn any precipitation to snow.

The low over the Southwest will stretch and elongate over the
entire region as the next low over the Aleutians presses east.
Enough upslope forcing will allow some snow showers to linger
throughout the entire southwest as the flow transitions to
northerly and northwesterly on Friday into Saturday, especially
along the Aleutian and Alaska Range.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Day 1 through 3:
Tonight through Sun)...

Broad area of northerly flow through the Bering Sea to Central
and Eastern Aleutians tonight. Heavy freezing spray over the
Northern Bering and near the ice edge will continue.

A low over Southwest Alaska will elongate and stretch into the
Bering Sea as a North Pacific low presses north and east through
the short term. That said, lingering snow showers will remain
possible. After midnight Friday into Saturday, easterly winds will
increase to storm force potential as the low presses into the
Western and Central Aleutians by Saturday afternoon. Precipitation
chances will increase with the passage of the front and any snow
will quickly transition to rain. The front appears to reach the
AKPen by Sunday afternoon with southerly flow.

&&

.Marine (Days 3 through 5: Sunday through Tuesday)...

Gulf of Alaska: A weak area of high pressure will maintain winds
less than 35 kts and seas less than 20 ft for the Day 3 through 5
period.

Bering Sea: A broad area of low pressure settling across the
western Aleutians to the North Pacific will remain stationary
through early next week. Small, embedded disturbances circulating
around the broad low will bring gale force winds and seas above 20
ft at times for south of the Aleutians and much of the Bering Sea
through Tuesday.

.Long Term Discussion (Days 4 through 7: Monday through Thursday)...

Overall, the latest operational model runs are in decent agreement
with the evolution and progression of the synoptic scale features
for early next week but diverge in the specific details towards
the end of the period. For Southcentral, high pressure building
over the Gulf of Alaska will leave a brief period of dry weather
from Monday through Wednesday. The rest of the mainland, including
coastal and interior Southwest, is expected to be relatively dry
with near to below normal temperatures as the ridge axis extends
north of the Alaska Peninsula to the eastern Bering Sea. Beginning
on Wednesday, models seem to key on a frontal boundary extending
from the center of a North Pacific low, bringing precipitation and
wind from Kodiak Island northward to the southern mainland. If
this scenario were to materialize, there is a potential that a
barrier jet will develop along the northern Gulf coast from Prince
William Sound to the Copper River Delta area. Where the
uncertainty emerges is the track, position, and timing of the low
and front that still needs to be ironed out with subsequent model
runs. Out west, a broad trough will settle across the western
Aleutians to the North Pacific. Weak, embedded shortwaves and
surface lows moving upstream of the trough will bring a wintry mix
of rain/snow and gusty winds at times along the southern portion
of the Aleutians into the Bering Sea. Depending on the track and
positions of these shortwaves, this could also bring widespread
precipitation to the eastern Aleutians and the southwestern
mainland later next week.

&&
.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...Winter Storm Warning 125.
		 Winter Weather Advisory 141.
MARINE...Gale 119 125 131 132 177 178.
		 Heavy Freezing Spray 185.
FIRE WEATHER...NONE.

&&

SYNOPSIS AND MODEL DISCUSSION...TM
SOUTHCENTRAL ALASKA...KO
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...VR
MARINE/LONG TERM...MF