Gale Warning 61, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
525 AM AKST Thu Jan 19 2023

.ANALYSIS AND UPPER LEVELS...

The pattern remains amplified. An upper level low currently
extends across eastern Siberia and across the Bering Strait. A
series of upper level troughs are currently lifting northward
across Southcentral and Southwest Alaska.

Closer to the surface, radar imagery shows rain moving northward
across the Gulf of Alaska into Prince William Sound. Another area
of showers is currently lingering across the northern Alaska
Peninsula.

&&

.MODEL DISCUSSION...

Forecast confidence overall is average as guidance has a decent
handle on the placement of synoptic scale features. However, the
smaller scale mesoscale features continue to pose a forecast
challenge. The other challenge continues to be the timing of
precipitation across Southcentral.

&&

.AVIATION...
PANC...VFR conditions and light winds will persist for this TAF
package. Temporary IFR conditions are possible in areas of low
stratus through 18z this morning.

&&

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

A broad and elongated low pressure system is moving into the
western Gulf this morning. Precipitation is falling along the
northern Gulf coast and Kodiak this morning. A series of
shortwaves moving southeast to northwest will move across
Southcentral over the next few days. The track and position of the
low as it moves through the Gulf will be the biggest factor in
the orientation of the frontal boundaries, coupled with the
direction of the winds and the balance between onshore versus
offshore flow. These considerations will affect the outcome for
the precipitation type, especially for communities along the coast
and gaps effected by terrain and south to southeasterly flow.
Late tonight through Friday morning, winds look to turn
southeasterly and areas along the Gulf coast and through Turnagain
Arm could see a mix of rain and snow. Each successive wave could
bring more warm air through and transition some areas to rain for
a period. Friday afternoon, winds should shift to some sort of
northerly and bring cooler air back to the area through Saturday.
By Saturday night, a ridge will build from west to east across
Southcentral.

&&

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

Scattered snow showers look to continue along the Alaska Peninsula
(especially the central AKPEN) today today through Friday night as
cold air advection from from the northwest continues on the
backside of an eastward moving North Pacific low headed to the
Gulf of Alaska. Winds could be stronger and gusty through the gaps
and passes along the North Pacific side of the AKPEN especially
from Friday afternoon through Saturday morning. Meanwhile, light
snow is possible this afternoon for portions of Bristol Bay, the
interior Kuskokwim Delta, as well as the lower Kuskokwim Valley as
a series of weak shortwaves within the broader upper-level trough
lift northward out of the North Pacific and traverse southwest
Alaska. Any snow accumulations are expected to be light and not
impactful. Upper ridging, along with quiet weather, builds in from
the Bering Sea Friday night as the upper pattern begins to
amplify. Low temperatures Friday night could be quite cold as
strong northerly flow through a good portion of the atmospheric
column takes hold of mainland Southwest. Portions of the Kuskokwim
Delta and lower Kuskokwim Valley could get down as low as the
negative teens. Depending on the wind magnitude coupled with off-
shore flow from the northeast, wind-chills will have to be
monitored closely for those areas. The next weather-maker arrives
Saturday night when a North Pacific low pushes its front northward
into the AKPEN. A period of snow looks likely at the onset, but
warmer air could work in depending on how far north the front
actually goes. Stay tuned for further updates as the overall
active pattern looks to continue.

&&

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

The overall active weather pattern for the Bering Sea and the
Aleutian Chain looks to continue through the short-term period.
Convective snow showers for the Pribilof Islands, central Chain,
and eastern Chain through tonight before the pattern begins to
amplify and an upper-level ridge builds northward into the central
Bering from the North Pacific. However, the western Chain will
remain active and under the influence of an upper-level low and
surface low bringing snow showers and gusty gale-force winds to
the area Friday morning through the evening hours as the surface
low moves northwestward. There could even be some storm-force
winds over the off-shore marine zones Friday night through
Saturday morning The pressure gradient tightens between this
departing low and ridging in the eastern Bering to produce a
corridor of gales over the central Chain and eventually the
eastern Chain Friday afternoon through the rest of the short-term.
These winds eventually turn to the east/northeast as yet another
North Pacific low and front lift northward to the Chain Saturday
morning and lingers through the weekend. Rain and rain/snow mix
look likely with this system as warmer air moves in from the
south. There is still some uncertainty though with exact track and
timing of this system. Stay tuned for further forecast updates.

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

An active pattern remains likely for the first half of the coming
week, but most of the details are getting lost in the complex
interaction between a handful of key features that continues to
prove a struggle for models. By the start of the period on
Sunday, models are all showing that a polar low harboring frigid,
Arctic air over Siberia will become displaced by a ridge
developing over the Bering in the short term, resulting in the low
and it's associated Arctic air moving west into the Interior and
North Slope by the end of the weekend. Another large, synoptic low
will be approaching the eastern Aleutians and Alaska Peninsula
from the south by Sunday as well. The resulting pressure gradient
between the low and strong ridge over the northern Bering will
drive a broad swath of northeasterly gale force winds across an
impressive chunk of the Bering Sea, with sustained gales likely
persisting into Monday. An deep frontal zone will extend into the
Gulf east of the center, with a new low likely to form at the
front's triple point somewhere south of the Kenai Peninsula or
Kodiak Island by Sunday evening. Heavy precipitation will spread
into the northern Gulf Coast and Prince William Sound region along
and ahead of this front as a surge of moisture and lift spreads
north through Monday.

From late Monday onwards, the overall outlook becomes increasingly
blurry, with models diverging markedly with the handling of the
Arctic low/trough over northern Alaska. The most recent suite of
operational model runs is showing the low becoming squeezed
between the blocking high over the Bering and another upper ridge
extending into northwestern Canada along a northeast to southwest
axis. Depending on how far the trough becomes stretched to the
south, very cold air could spill down into Southwest Alaska between
Monday and Tuesday, perhaps lingering into Wednesday or later. A
large baroclinic zone will set up to the south across the Gulf and
into Southcentral, with much warmer, moist and southwesterly flow
continuing to push northeast around the upstream ridge. This
should favor continued moderate to heavy snow and coastal rain
across much of the Prince William Sound region, perhaps extending
farther north at times into Southcentral and Bristol Bay. The more
northward extent of snowfall will depend on exactly where the
clash between the Arctic air spilling into the Bering/Southwest
and warmer, maritime air over the Gulf sets up, which remains
highly uncertain.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...Heavy Freezing Spray Warning 160 179 180 185 412 414.
Gale Warning 119 120 130 131 132 139 150 175 176 177 178 411 412 413.
FIRE WEATHER...NONE.

&&

SYNOPSIS AND MODEL DISCUSSION...ED
SOUTHCENTRAL ALASKA...VR
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...DAN
LONG TERM...AS