Gale Warning 346, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
506 AM AKDT Wed Apr 20 2022

.ANALYSIS AND UPPER LEVELS...

High pressure remains over Central/Northern Alaska, with weak low
pressure over the Gulf, generating a bit of a Rex Block pattern
for the time being. Easterly flow will continue across the
northern Gulf with an offshore flow pattern in place across
Southcentral. A storm force low tracks near the Western Aleutians
early this morning. The system then moves eastward, spending the
next few days traveling towards the Gulf of Alaska. The associated
front moves along the Aleutian Chain and across the AKPen today
through Thursday, bringing rounds of precipitation and winds to
the aforementioned areas. The front then extends into the southern
Gulf by Thursday afternoon, mustering up some active weather for
Kodiak Island and areas along the North Gulf Coast by the end of
the week.

&&

.MODEL DISCUSSION...

Models remain in good overall synoptic agreement through the short
term. Solutions continue to get a better handle on the complex
system moving south of the Chain through the rest of the week.
There are still some notable differences in the embedded mesolows
but overall those differences will not be significantly impactful.

&&

.AVIATION...

PANC...VFR conditions and light winds will persist.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 through 3/Today
through Friday night)...

An upper level low tracking overhead of Southcentral will continue
to drift slowly westward, exiting into Southwest Alaska on
Thursday. Similar to yesterday, there isn't enough forcing or
instability to produce any showers inland. However, flow on the
back side of the upper level low will bring an inverted surface
trough and associated showers from the eastern Gulf of Alaska
northwestward to the Cordova/Valdez area today. These showers
will then be advected westward toward the eastern Kenai Peninsula
this afternoon and evening. Showers likely won't make it over the
Kenai and Chugach Mountains, with a very dry air mass in place -
but can't rule out stray shower. While most of the region will
start out sunny, do expect a few clouds to advect across
Southcentral this afternoon and evening.

All eyes then shifts to a large and deep low tracking eastward
along the Aleutian chain. A leading occluded front will reach
Kodiak Island and the western Gulf of Alaska Thursday afternoon
and evening, with rain and winds spreading northward. Steady
upslope precipitation will develop over western Prince William
Sound/eastern Kenai Peninsula Thursday night, with heavier frontal
precipitation arriving Friday and persisting through Friday night.
Snow levels will start out low, roughly around 500 feet Thursday
night. However, they will rise to over 1000 feet on Friday as the
front nears. Strong low level easterly flow combined with weak
dynamics aloft (as the low center remains well to the south) will
keep inland areas of Southcentral dry, albeit with considerable
cloudiness. This will be the strongest front to impact the region
in quite sometime, producing widespread gales across the Gulf
coastal waters Thursday night through Friday night. Also expect
the typical gap winds through Turnagain Arm and parts of the
Matanuska Valley.

&&

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

A closed upper low over the Southern Mainland will slowly move
northeast over the next two days before shearing apart as it
interacts with a large low over the Bering and a trough moving
east out of Russia. To the south of the low center, onshore flow
and a few weak mid-level shortwaves will produce some showers over
Bristol Bay that will move north into the Interior and Kuskokwim
Mountains this evening. As the upper low pushes north Thursday
morning, a front moving east across the Alaska Peninsula will
increase winds through the southeasterly gaps. Flow aloft will be
out of the east-southeast, resulting in some spillover of
precipitation from Pilot Point south Thursday afternoon through
Friday morning. Interior Bristol Bay is likely to see some rain
Friday as the front reaches Kamishak Gap and downsloping and
mountain blocking have less of an effect on the region. The
Kuskokwim Delta and Lower Kuskokwim Valley may see a sprinkle
here and there but overall should remain relatively dry and
overcast in the coming days.

&&

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

Two upper lows and corresponding surface lows are in the process
of merging south of Shemya this morning. Winds are expected to
intensify to storm force near Amchitka as eastern and primary low
taps into colder air between and to the north of the two lows. In
the warm sector, gale force winds and rain will moves slowly
across the Chain over the next two days. Some snow showers are
possible within the cold sector as the low moves east, but most of
this activity appears to be south of the Chain at this time.
Gusty easterly winds and snow are expected over the Pribilof
Islands Thursday morning, but warmer temperatures should cause
the snow to stick to the ground, thus mitigating potential for
blowing snow. By Friday the storm should be mostly out of the
area, making way for calm and partly sunny conditions.

&&.Marine (Days 3 through 5: Friday through Sunday)...

Gulf of Alaska: Low pressure south of Kodiak Island will extend
a front to the northern Gulf for Friday. Easterly winds of 20 to
30 kt with low end gales up to 40 kt are possible from the Barren
Islands to Kayak Island for Friday into early Saturday as a
barrier jet forms ahead of the front. Winds will then diminish
through Saturday as the front weakens. Waves of 5 to 10 ft will
prevail across much of the Gulf, with waves along the northern
Gulf building to 10 to 15 ft along the northern Gulf for Friday
into early Saturday in association with the strongest winds.
Forecast confidence for this outlook is high.

Bering Sea: A north Pacific low south of the Aleutian Chain will
move east into the western Gulf through Friday. Widespread
easterly winds of 20 to 30 kt from Bristol Bay to the Pribilof
Islands Friday morning will turn more northerly and diminish
through the day. Northwesterly gales are likely along the backside
of the low, with these winds diminishing across the central
Aleutians by late Friday and the eastern Aleutians on Saturday.
Seas of 10 to 15 ft are expected across the southern Bering with
seas of 15 to 20 ft possible on the Pacific side of the central
and eastern Aleutians through Friday. Seas will subside to less
than 10 ft Saturday into Sunday. Southerly winds increase to 20 to
30 kt with seas building to 10 to 15 ft across the western
Aleutians/Bering for Monday in advance of a Kamchatka Low.
Forecast confidence for this outlook is high.

&&

Long Term Discussion (Days 4 through 7: Saturday through Tuesday)...

A large upper-level trough extends from eastern Russia south and east
to the Gulf of Alaska, bookended by a retreating upper-level
ridge downstream over the Canadian Rockies and a second ridge
building over the western Aleutians. The trough is anchored by an
upper-level low situated at its base, weakening and moving east
from south of the AKPen to the southeast Gulf of Alaska through
the weekend. By Monday, this feature slides farther south as the
aforementioned ridges strengthen and phase into a larger blocking
ridge, extending from the central Aleutians to the Canadian
Arctic. A series of shortwaves moves from the western Bering to
the west coast of the state through Tuesday; however, these weaken
quickly as the ridge remains over much of the state.

At the surface, this translates to an area of low pressure moving
from well south of Kodiak Island Saturday to the eastern Gulf by
Sunday, exiting the region for Monday. Its associated front will
remain along over the northern Gulf through early Sunday, keeping
conditions unsettled. However, the front falls apart and
conditions improve for the second half of the weekend and into the
next work week as the ridge builds and a northerly flow ushers in
a drier airmass. Clouds may linger across interior Southwest
Alaska Sunday as the first of two shortwaves moves onshore and
weakens. As the ridge axis moves over Kodiak Island and extends
northeast for Monday, the resulting southwesterly flow in its wake
will bring clouds and a few showers to the Kuskokwim Delta Monday
into Tuesday as the second wave approaches the coast.

With the bulk of the unsettled weather remaining along the coast and
a ridge building over much of the Southern Mainland, expect a
gradual warming trend for Southcentral into next week. Average
temperatures this week will climb above average through the
weekend and into early next week. Daytime highs are expected to
push into the mid to upper 50s across interior Southcentral and
into the low 50s along the coast. For Southwest Alaska, expect
daytime highs in the mid to upper 40s inland and in the upper 30s
to low 40s along the coast, as higher cloud cover and an onshore
wind limit the amount of warming.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...Storm Warning 177 178
		 Gale Warning 132 150 155 160 165 170-176 179 180 411-414
FIRE WEATHER...NONE.

&&

SYNOPSIS AND MODEL DISCUSSION...KM
SOUTHCENTRAL ALASKA...SB
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...CJ
MARINE/LONG TERM...TM