Gale Warning 468, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
447 AM AKDT Mon Sep 23 2019

.ANALYSIS AND UPPER LEVELS...

A rapidly developing low pressure system centered south of Kodiak
Island has deepened into the lower 970 millibar range early this
morning and is tracking to the east through the southern Gulf. Its
associated frontal system stretches from Kodiak Island east
across the central Gulf. Northwesterly gales of 40 to 45 kt with
storm force gusts are occurring along the west side of the low
with gusts up to 60 kt through the gaps and passes in the Alaska
Peninsula with easterly gales along the front to the north. Over
Southcentral Alaska weak upper level ridging is building in, while
broad troughing persists over the Bering.

&&

.MODEL DISCUSSION...

Models continue to be in good agreement regarding the main low
pressure tracking from west to east across the southern Gulf today
but still struggle with the location of potential triple point low
development along the main front stretched across the central
Gulf. Once the low exits the Gulf on Tuesday, model agreement
remains good through Wednesday night.

&&

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

&&

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

A low moving into the Gulf will lead to winds increasing through
this afternoon along coastal areas. Strongest winds of up to 40
mph are possible extending eastward from Kodiak Island. Most of
the associated precipitation is expected to remain offshore, with
partly to mostly sunny skies and light winds persisting today
across much of the interior. Clouds will increase Tuesday as an
upper level trough moves into the area. As the vort max moves
through Anchorage and the Mat-Su around midnight Wednesday
morning, brief light showers will be likely. The parent upper
level low will descend into Southcentral from the north by
Wednesday afternoon, trending temperatures downward. Rain
continues to be the dominant precipitation type associated with
this feature, though higher-elevation snow is likely especially as
it cools Wednesday evening. Snow is also possible in the Copper
River Basin as the low tracks farther east.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1-3: Mon-Wed)...

A low in the Gulf will continue to produce a few showers and
gusty conditions across coastal regions of Bristol Bay and the
Alaska Peninsula today. An upper level trough will move into
Southwest Alaska through Tuesday afternoon, which will bring stronger
winds and another round of rain, and possibly a trace of snow to
higher elevations, for Tuesday evening. This shortwave will also
bring near freezing temperatures for the Kuskokwim Delta and
Valley overnight tonight and cooler high temperatures for Tuesday
afternoon. The rainy pattern will continue through the first part
of Wednesday as this feature strengthens and moves farther
inland.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1-3: Mon-Wed)...

Gale force winds on the back side of the Gulf low remain across
the Alaska Peninsula, which will diminish to small crafts through
this afternoon. The north-northwest flow will keep possible gusts
up to 50 kts out of bays and passes, which will taper off
throughout the early afternoon hours.

Behind this feature across the central Bering, a new feature will
bring a swath of small craft winds for Tuesday morning. The winds
will increase as they approach the Southwest coast by Tuesday
afternoon, evening bringing a small area of gale force winds
along the Kuskokwim Delta coast and moving into Bristol Bay late
Tuesday.

Attention quickly shifts to the strong system moving in over the
western Bering and Aleutians by Tuesday afternoon. This front will
bring strong, southerly gale force winds as it progresses
eastward, with the potential for storm force winds. As the front
continues into the central and eastern Bering, winds will weaken
to low end gales through Wednesday.

&&

.MARINE (Days 3 through 5)...

Beginning the extended period marine forecast on Wednesday, there
will be a broad area of westerly cold air advection across the
Gulf of Alaska with gale force winds coming out of the Barren
Islands. Given the generally longer fetch, seas will likely be in
the 10-15 foot range across the Gulf into Thursday before high
pressure moves in Thu night.

Over the Bering Sea, there will be a large cyclone slowly moving
across the Bering Sea, with broad southerly flow encompassing the
entire area as the front slowly shifts eastward, reaching the
west coast by Wed night and Thu. This storm will bring quite a bit
of swell into the Bering, so expect widespread seas of 15-20 feet
with some potential for higher seas over the far western Bering
Sea.

&&

.LONG TERM FORECAST (Days 3 through 7)...

Beginning the extended period forecast on Tuesday evening, there
will be an active pattern in place over the Southern Mainland as a
series of mobile shortwave troughs will be moving east. This will
keep an active threat for rain, although light in nature across
most regions, as well as higher elevation snow (3000+ feet)
favoring the Talkeetnas/Chugach/Alaska Range. One shortwave
trough looks to move east Tue night across Southcentral with
another secondary wave tracking across Southwest Alaska. The
shortwave trough shifts east on Thu, and there is much less
certainty on the second, especially as it tracks into
Southcentral. Given the west flow regime, precipitation will
likely more favor the mountains and north Susitna Valley and
Copper Basin with a quick hit of rain and more higher elevations
snow. Westerly cold air advection will push stronger winds through
the Barrens and some local gaps, and will also dry the region out
as offshore winds increase Wed night.

Expect high pressure to dominate with dry weather through early
Saturday before the next Pacific low spreads more clouds and
moisture into Southern Alaska. Timing is uncertain, but most
global guidance favors increased rain chances for Southwest by
Saturday morning with chances increasing for Southcentral by
Sunday. This low will be tapping deep subtropical moisture and
will be a longer, slower moving trough, so this could be a high
rain maker Sunday through Tuesday.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...Gale Warning...119 130 131 132 155 178 180 351.
FIRE WEATHER...NONE.

&&

SYNOPSIS AND MODEL DISCUSSION...JER
SOUTHCENTRAL ALASKA...AP
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...AH
MARINE/LONG TERM...JA