Gale Warning 811, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
439 AM AKST Thu Dec 24 2020

.ANALYSIS AND UPPER LEVELS...
The longwave trough extends from mainland Alaska to the western
Bering. There is a surface low north of Bethel, another surface
low south of Sand Point and a cluster of lows in the Western
Bering with the front east of Adak. The radars at Bethel, King
Salmon, Kenai and Middleton Island all have showers on them early
this morning. Lightning was detected northeast of Adak overnight.
On ASCAT (Advanced Scatterometer) imagery gale and storm force
winds were detected near Shemya and there is a second area of
gales and storm force winds south of the AKPEN.

&&

.MODEL DISCUSSION...
The models are struggling in the first 48 hr forecast period. The
discrepancies are apparent at the surface and at 500 mb (the
middle atmosphere). This is impacting the placement and the
intensity of the surface lows as well as the p-type (rain vs.
snow). Overall, the North Pacific and the Bering continue to be
active with multiple lows the next 96 hrs. Updates to the forecast
will be made as needed.

&&

.AVIATION...
PANC...The Kenai radar has pinged into showers over portions of
Cook Inlet. The models show some of this moisture moving up Cook
Inlet and near the aerodrome. The models also show a finger of the
jet moving directly over PANC by 18z today. And by 3z Friday this
jet sliver will be over Denali and Fairbanks. Generally expecting
VFR conditions this TAF package. However, based on the
observations at PAEN overnight, if moves across PANC the category
could briefly drop below VFR.

&&

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

A quiet weather pattern is expected for Southcentral AK,
especially for inland areas. The exception will be Kodiak and the
Southern Kenai Peninsula, as a low pressure currently moving into
the Western Gulf will provide precipitation and windy conditions.
Gale force winds can be expected from this system, with highest
winds in gaps and passes. Another low is anticipated to move into
the Northeastern Gulf on Saturday, following the coastline up from
the panhandle. This low still has a lot of uncertainty associated
with it, so more to come on this low as the weekend approaches.
Right now it looks gale force at most and is confined to the coast.

The only significant weather for the rest of mainland AK is that a
high presure setup over Interior Southcentral and low pressure in
the Gulf will cause off-shore winds to blow down the Cook Inlet
and through other gaps around Valdez and the Copper River Delta.
The Mat Valley wind is also expected to pick up. These winds will
be aided by cooler temperatures in the Copper River Basin.
Otherwise, expect quiet weather and pleasant temperatures the next
few days for your holiday festivities.

&&

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

Bands of snow showers along with gusty northwesterly winds will
persist from Hooper Bay south to Kuskokwim Bay this morning in
the wake of a compact are of low pressure lifting toward Norton
Sound. As it departs the YK-Delta today, cloud cover and winds
will be on a downward trend from the Kuskokwim Delta coast to the
Kuskokwim Valley as a ridge extends over the region tonight. This
ridge will be quickly pushed to the north for Friday as an area of
low pressure south of Kodiak Island this morning tracks to
Bristol Bay.

As the low tracks north, clouds will quickly increase with snow
developing over the AKPEN later today. Snow will then spread over
Bristol Bay and the Middle Kuskokwim Valley by early Friday
morning. Gusty northeasterly winds will also develop in
association with the low, allowing for period of drifting and
blowing snow, especially from Dillingham to Koliganek where the
highest snowfall totals are expected. Snow and gusty winds will
then increase over the Kuskokwim Delta early Friday morning, with
areas of blowing snow also possible. Snow totals are not expected
to be as high, maybe an inch or two, but the colder air in place
will make for a drier snow, thus allowing for better transport.

The low will stall over Bristol Bay through Friday with light snow
continuing across the Southwest coast. Bands of snow showers will
also be likely from Port Heiden to Cold Bay, with reduced
visibilities at times in heavy snow bands, as colder air and
moistures wraps around the back side of the low. The low finally
weakens and moves onshore near Dillingham on Saturday with
scattered snow showers lingering over the higher terrain. The next
weather front will move toward the AKPEN and Southwest coast for
Sunday with gusty southeasterly winds and mixed precipitation.

&&

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

A ridge over the eastern Bering today will be replaced by an area
of low pressure moving over Bristol Bay from south of Kodiak
Island. Colder air wrapping around the low will usher colder air
south across the eastern half of the Bering through late
Saturday, enhancing show shower activity from Nunivak Island south
to the AKPEN.

Farther west, a complex low with multiple centers of circulation
continues to move southeast from the western Bering to the central
and eastern Aleutians through late Friday. Areas of gales and
storm-force winds will wrap around the western periphery of these
lows as they pull colder air over the Bering from Siberia. The
first of these lows will slide a front across the Chain today,
with gusty northwesterly winds and bands of heavy snow showers
developing behind the front closer to the low. These snow showers
could reduce visibility at times to near one half mile for places
like Adak and Atka through early Friday morning.

A rapidly deepening North Pacific low will then push a front to
the western Aleutians by late Friday. The low itself will deepen
to around 940 mb as it crosses the Rat Islands by Saturday morning
with a wide area of storm force winds, and perhaps smaller areas
of hurricane-force winds, developing both along the front over the
Bering and wrapping underneath the low. This low will then slow
and become nearly stationary somewhere near Shemya as it deepens
to a near 930 mb low with storm force-winds covering a wide area
of the western Bering and Aleutians. This system will push a front
across the central and eastern Bering late Saturday into Sunday
with widespread rain and snow along with gales from Saint Paul to
Dutch Harbor and Cold Bay.

&&

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

Gulf of Alaska:  No significant winds/seas are expected on Saturday.
On Sunday some small craft southerlies work into the western Gulf
as a weakening front moves in from the west. There is some upside
risk to lower end Gales around the Barren Islands. On Monday
generally small craft easterlies are expected across the Gulf, but
there will continue to be a risk for Gales for southern portions
of the Cook Inlet.

Bering Sea: On Saturday a powerful area of low pressure sets up
across the western Bering with a gale force front extending
through the central Bering into the eastern Aleutians. Models
continue to struggle with the exact placement of this front and
the overall intensification rate of this low, but future forecasts
may need the introduction of storm force winds along a good
portion of this front (up from the current widespread Gales). On
Sunday and Monday this low remains mostly stationary across the
western Bering, but models indicate that a few smaller areas of
low pressure may rotate around this larger low, which could result
in some compact areas of Gales or even storm force winds across
portions of the Bering/Aleutians, but pinning down the
location/timing of these lows remains difficult at this range.

&&

.LONG TERM FORECAST (Days 3 through 7: Sunday through Wednesday)...

The biggest feature in the long term will be the broad and persistent
low across the western Bering. This low will have a broad occluded
front extending through Southwest Alaska and the AKPen on Sunday,
with this front lifting towards the Northern Gulf Coast Sunday
night into Monday. This front will bring a wintry mix to southwest
AK, and another round of higher elevation snows to the Eastern
Kenai and Prince William Sound, but with minimal impacts for areas
further interior. For Tuesday and Wednesday a few compact lows
look to continue to pivot around a broader low across the Bering
continuing the unsettled pattern there. Relatively quiet conditions
will be found across the Gulf of Alaska and Southcentral. A welcome
break from the extremely active pattern we have been in as of
late.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...Storm 413173 175. Gale 130 131 132 136 352 411 412 150
155 172 174 176 177 178. Heavy Freezing Spray 180 181.

&&

SYNOPSIS AND MODEL DISCUSSION...PJS
SOUTHCENTRAL ALASKA...BJB
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...TM
MARINE/LONG TERM...BG