Gale Warning 68, NWS Anchorage, AK

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

.ANALYSIS AND UPPER LEVELS...

A strong upper level low with its corresponding surface low is
currently located due south of Sand Point and is moving rapidly
northward this morning. To the east of this low is deep, moist,
southerly flow which is advecting moisture (total precipitable
water) that is 170% of normal for this time of the year.
Therefore, this system is sending loads of moisture northward.
Looking at the CIMSS Mimic Precipitable water imagery this
morning, you can notice a narrow corridor of high moisture content
being brought northward from the latitude of around Hawaii and
aimed at southern Alaska, in particular, the eastern Kenai
Peninsula and western Prince William Sound. The front associated
with this system is currently moving through the southern Gulf
increasing the winds in this area. Portage was gusting out ahead
of this main front already this morning with gusts as high as 61
mph or 53 kts. Besides the strong low, conditions across the rest
of Southcentral remain rather quiet with a few snow showers making
it over the mountains bringing some flakes to Anchorage as well
as portions of the Western Kenai Peninsula. Temperatures area-wide
are also much warmer than that of recent with most areas in the
20s to around 30 degrees. The only cold spot remains across the
Copper River Basin where temperatures are still in the single
numbers below to single numbers above zero. Kenai was also
reporting freezing fog for a good portion of the overnight where
visibility dropped to as low as one quarter mile at times.

Across Southwest, mid to high level clouds are streaming into
the area as the aforementioned storm system continues moving
northward. Temperatures mostly were in the teens and 20s with the
coldest temperatures across the Kuskokwim Delta.

Northerly to northeasterly flow continues across the Bering. As a
result, Arctic air continues to flow off the ice edge and over
the relatively warm water surface creating for unstable
conditions causing occasional snow showers under the
stratus/stratocumulus deck over the Bering. Heavy freezing spray
also is continuing as a result of the Arctic air, especially near
the ice edge.

&&

.MODEL DISCUSSION...

Model guidance is overall in good agreement out through Friday
evening before beginning to diverge. Overall, model guidance
remains consistent on the movement of the upper level features and
surface features with the current storm system moving northward
through the Gulf this morning. Models diverge beginning Friday
evening with a shortwave trough that will be over the Bering.
There looks to be timing differences along with how exactly the
upper level energy will move across Southern Alaska from Fri
evening and through the first half of the weekend. As a result,
this will cause drastic changes to the sensible weather expected
during this time period. Model guidance is in rather good
agreement on another gale force low (potentially storm force)
moving into the Aleutian Island Chain/Bering Sea Friday evening
and through the weekend. The main thing is determining if the
front will be storm force with this system.

&&

.AVIATION...

PANC...VFR conditions are mostly expected throughout the TAF
package, though, brief ceilings to 5000' are possible. However,
gusty northerly winds are expected to develop later this morning
around 16z with gusts up to 20 kts. Winds are expected to remain
gusty through around 14/00z before beginning to diminish to around
10kts. Winds continue to diminish through the evening and
overnight hours. Though, expect southeasterly winds around 2000 ft
causing wind shear over the terminal. There is expected to be an
increase in wind shear for the 14/00-06z time frame before
diminishing some after 06z but wind shear will remain.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 and 2...Thursday
and Friday)...

An impressive storm system is moving north through the Gulf and
impinging upon the north Gulf coast. This storm will bring a
little bit of everything in terms of hazardous weather-winds,
heavy precipitation, and snow at higher elevations. The upper
level jet helping to support it is dragging up moisture and warm
air from as far south as 40N.

For marine areas, widespread gales have already developed. As the
system intensifies and moves closer, we have hoisted some Storm
Warnings out for many of the typical areas (Barren Islands, coast
near Cordova). Gusty east to southeast winds will accompany the
front as it converges with the coast. Gusts are expected to peak
in Turnagain Arm and the Portage Valley with 80 mph possible.
These strong winds along the front will initially be held in check
further inland as strong north- northeast winds will hold.
Anchorage and the Mat Valley should expect gusty north winds to
develop through the day, with the Mat Valley peaking in the 35-45
mph range. The Anchorage Hillside will represent the boundary
between these opposing winds. We expect southeast winds to gust
near 50 mph later today for that area.

Precipitation has already started from Kodiak through Whittier
over to Cordova. While Kodiak initially started out with some
snow, warm air off the Gulf has turned conditions to rain for the
island. This will be the theme as the area of low pressure drives
quickly north through the day. Warm air will slowly creep in and
push temperatures over the freezing mark. So while many locations
at sea level will see an initial burst of snow, it should change
over to at least a rain/snow mix (if not all rain) by this
evening. Snow levels should climb slightly above 1,000 ft during
the peak of the storm. This will leave many of the passes
vulnerable to some intense periods of heavy, wet snow today. Thus,
a Winter Storm Warning remains in effect for parts of the Seward
Highway, to include Turnagain Pass. Further inland, the Susitna
Valley and Copper River Basin will hold onto their cold air during
this event. A Winter Weather Advisory has been issued for the
southern portions of the Copper River Basin. The far western
slopes of the Susitna Valley could see 1-2 feet of new
accumulation.

The low center will track up Cook Inlet Fri morning. This will
shift winds across the area. The shift from more easterly to
southerly for Seward will allow for increasing rain rates. Due to
this change, we have increased QPF rates for the Seward area to
over 3 inches by Friday evening. For Anchorage, the low track will
allow for a period of gusty southeast winds to push across town.
These winds will cause temperatures to jump quickly to near 40
degrees.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Day 1 through 3: Today
through Sat night)...

A surface low approaches the AKPEN Thursday, bringing a surge of
warmer temperatures and areas of precipitation. Temperatures on
Thursday will peak in the 30s for Bristol Bay and climb into the
20s for the Kuskokwim Delta and Lower Kuskokwim Valley. Most of
the precipitation will fall as light snow along the Aleutian Range
and Kuskokwim Mountains, with totals ranging from 1 to 3 inches.
Increasing winds with this front will bring the potential for
blowing snow.

The biggest uncertainty with this system is whether
downslope areas such as King Salmon will see much precipitation
and, if so, what type. The most difficult location to pin down is
King Salmon. For now, the thinking is that downsloping will make
precipitation less likely. There could be a brief period of
freezing rain Thursday afternoon and evening, but any
precipitation that falls in King Salmon is expected to be mostly
snow.

By Friday morning, the low will weaken as it enters the Southwest.
Northerly flow around the backside of the low will draw in cooler
air, and temperatures will slowly drop through Saturday night.
Precipitation will transition to snow showers before tapering off
Saturday as a ridge moves in from the Bering.

&&

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

A surface low approaches the AKPEN Thursday. Winds will become
northerly in the Eastern Aleutians, with gusty winds through gaps
and passes. Otherwise, conditions remain largely unchanged across
the remainder of the Aleutian Chain and Bering Sea; a snow and
rain/snow shower regime, broad northerly flow, and heavy freezing
spray over the Northern Bering and near the ice edge will
continue.

By Friday morning, the low tracks into Southwest Alaska and
weakens. Winds in the Bering Sea shift and become westerly as a
result of this low and a developing ridge. As such, freezing spray
across the Eastern Bering will be reduced by Friday night. In
addition, the probability of snow showers increases Friday as a
shortwave transits from the Central to Eastern Aleutians.

Further west, winds increase on Friday night as a North Pacific
low pushes its front into the Western Aleutians. The front tracks
towards the Central Aleutians by Saturday night, bringing rain and
widespread gales. Localized areas of storm-force winds will be
possible in the Western Bering.

&&

.Marine (Days 3 through 5: Saturday through Monday)...

Gulf of Alaska: Expect winds less than 35 kts and seas less than
20 ft for the Day 3 through 5 period.

Bering Sea: An area of low pressure will track from the North
Pacific and enter the western Bering Sea starting on Saturday, and
then remain stationary through early next week. A swath of gale
force winds and seas above 20 ft at times are expected for south
of the Aleutians and much of the Bering Sea at least through
Monday.

&&

.Long Term Discussion (Days 4 through 7: Sunday through Wednesday)...

Looking ahead into the extended forecast, 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, most of the precipitation will shift east toward
the Panhandle as an area of low pressure near the Kenai Peninsula
starts to weaken, leaving a brief period of dry weather from
Sunday through Tuesday. The rest of the mainland, including
coastal and interior Southwest, is expected to be relatively dry
with near to below normal temperatures. Beginning on Wednesday,
models seem to hint on a frontal boundary extending from a center
of a low, bringing precipitation and wind from Kodiak Island
northward to the Alaska Peninsula, and into the southern mainland.
Where the uncertainty emerges is the track, position, and timing
of the front that still needs to be ironed out with subsequent
model runs. Out west, a stationary low near the western Aleutians
will keep a wintry mix of rain/snow and gusty winds at times along
the southern portion of the Aleutians into the Bering Sea through
the middle of next week.

&&
.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...Winter Storm Warning 125
 Winter Weather Advisory 141.
MARINE...Storm Warning 119 130 131
138 Gale Warning 351 352 150 155 120 125 132 139 140 Heavy
Freezing Spray Warning 412 414 185. FIRE WEATHER...NONE.

&&

SYNOPSIS AND MODEL DISCUSSION...MV
SOUTHCENTRAL ALASKA...MSO
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...KC
MARINE/LONG TERM...MF