Gale Warning 165, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
440 PM AKST Sun Feb 19 2023

.ANALYSIS AND UPPER LEVELS...

Blocked ridge over the Pacific has nudged up into Alaska this
morning. Areas of fog and low stratus appeared in different
locations across the mainland, some producing enough moisture for
snow flurries and freezing drizzle. Fog is also observed in the
Middle Kuskokwim and the Kuskokwim Delta. A fast moving shortwave
is riding up along the western side of the ridge. This is
partially tethered to the shortwave spinning off a western Bering
low. While the low is skirting that western edge of the Bering,
that shortwave is moving snowfall through St Paul this morning. It
appears to be a brief burst of precipitation. Cold convective
cumulus trails behind though.

&&

.MODEL DISCUSSION...

Consensus on the synoptic level is good. Resolving the embedded
shortwaves, especially across the Bering Sea and for features that
are riding along the western periphery of the ridge over the
Pacific are more uncertain. Some of the challenges for the short
term are deciphering the potential for fog for various locations
across the Mainland and wind, in terms of magnitude and impacts
over the next few days. As warmer air continues to advect under
southwesterly flow into Alaska, the transition in precipitation
type could pose challenge in some areas over Southwestern Alaska
for the forecast this week.

&&

.AVIATION...
PANC...Improvement to VFR is anticipated this afternoon.
Reduction to MVFR ceilings and visibility is likely to return
after dark and last until at least sunrise. IFR and LIFR is
possible in the morning. Light winds are likely to prevail.

&&

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

Lingering weak low pressure exists over the Gulf of Alaska this
evening. A North Pacific low tracks south of the Gulf towards the
Southeast Panhandle through Monday. Winds across the Gulf of
Alaska will increase to widespread small craft, with areas of gale
force winds being pulled through some of the gaps, including
Resurrection Bay, Passage Canal/Prince William Sound, and out of
the Copper River Delta, on Monday. Winds will also be increased
through the Barren Islands.

A building ridge will keep cool and dry conditions across
Southcentral over the next couple of days. Cold air advection will
drift out of the Interior down into Southcentral. Anticipate winds
to ramp in areas along the coast, mainly Seward, Valdez/Thompson
Pass, and Whitter/Portage through Monday night. Low clouds and
periods of fog are likely again overnight tonight and into Monday
morning along the western Kenai Peninsula, spilling north across
western Anchorage into the Mat-Su Valley.

&&

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

Quieter weather is in store heading into early next week as a
ridge of high pressure from the eastern Bering Sea moves overhead.
Low stratus and fog trapped underneath the ridge returns
overnight tonight, with conditions expected to improve Monday
morning. Meanwhile, a couple of shortwaves waves will briefly
bring light snow showers to the Kuskokwim Delta and northern
Bristol Bay, while a snow/rain mix to the Alaska Peninsula on
Monday.

For the rest of the workweek, an active weather pattern will get
underway as a series of storm systems impacts western Alaska. The
first system is associated with a North Pacific low approaching
from the Bering into the Chukchi Sea early Tuesday. Temperatures
are expected to climb into the mid to upper 30s as far north as
the Lower Kuskokwim Valley as moderate southerly winds move into
the region. Most of the precipitation will stay to the north, but
the Kuskokwim Delta and Bristol Bay will initially start out as
snow in the morning. By mid-afternoon, warmer temperatures at the
surface will help transition to a wintry mix and then all rain for
the rest of the region. However, there is some uncertainty about
precipitation type timing and transition.

After this system pushes northward, the next warmer system
arrives shortly afterwards on Wednesday. Precipitation type is
likely to be predominately be rain as the atmospheric column of
air warms above the surface for the entire forecast area. Stay
tuned for further updates.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 to 3: Tonight
through Wednesday)...

A trough extending from the Kamchatka Peninsula to the western
Bering Sea will remain anchored through Monday. A low pressure
system pushes northward tonight, bringing precipitation and gales
along the Aleutian Chain and Pribilof Islands.

A strong North Pacific low is expected to approach the western
Aleutians early Monday. The leading frontal boundary will
overspread the western Aleutians by Monday afternoon, bringing
gusty southerly winds, elevated seas, and heavy precipitation.
There is moderate to high confidence for widespread gale force
winds, with localized areas of storm force winds between Monday
and Tuesday morning. As low lifts into the western Bering Sea, the
strongest core of the winds may shift to the west-southwest,
thereby producing a terrain channeling effect for the central
Aleutians (including Adak and Atka). There is also the potential
for gusts to reach hurricane force during that timeframe as some
colder air wraps around the low. A High Wind Watch is in effect
for the region from late Monday night to Tuesday morning.
Precipitation will initially start as snow followed by moderate to
heavy rain as warmer air surges across the Aleutians.

As the low lifts northward on Tuesday, the Pribilofs can see
increasing southerly gales to storm force winds and precipitation
as well. Conditions are expected to improve briefly on Tuesday
followed by a second system arriving midweek. There remains some
uncertainty with the timing and track with the second system, so
stay tuned for further updates.

&&

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

A more marked pattern change towards much more mild and wetter
conditions earlier in the week will be nearing it's end by the
beginning of the outlook period on Thursday. By this time, models
are in reasonable agreement that the strong longwave ridge axis
extending into Mainland Alaska will begin to flatten out and begin
to retreat southeast as successive shortwaves ride over the ridge
from the Bering and help break down the ridge in place. This
should shift the deep fetch of southwest flow and the associated
moisture tap south towards the Gulf as a briefly more zonal
pattern takes shape through Friday, with an effective cold front
progressing across the Southwest into Southcentral, changing any
falling precipitation solidly over to snow. A marked cooling and
drying trend should continue into the weekend as a broad upper
trough shifts from the eastern Bering towards the Gulf and as
renewed longwave ridging develops upstream across the Bering and
Aleutians. Much of the region out west will remain fairly active,
however, with a series of lows likely to track into the
central/western Bering around the periphery of the flat ridge
gradually amplifying with time. The latest global model solutions
are hinting at perhaps another much larger and stronger low,
potentially storm force, entering the western Bering late on
Sunday.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...High Wind Watch 187.
MARINE...Gale 130-132 155 165 172 177 180-185.
		 Storm 170 173-176 179.
FIRE WEATHER...NONE.

&&

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