Small Craft Advisory 184, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion...CORRECTED
National Weather Service Anchorage AK
530 PM AKST Sun Feb 23 2020

Corrected typos

.ANALYSIS AND UPPER LEVELS...

The strong low just south of the central Aleutians is now
vertically stacked and is beginning to rapidly weaken. The jet
stream is strengthening the next developing low near 40N 150W
today and this developing low can be seen on satellite. This new
low will become the main low impacting the region over the next
few days.
High surface pressure over the mainland part of the state and a
weak low in the Gulf of Alaska are helping to bring strong
outflows winds through the terrain along the Gulf of Alaska. This
is also helping to bring dry air into the region.

&&

.MODEL DISCUSSION...
Models are still struggling with the low moving toward Kodiak
Monday night and beyond. The good news is that they are trending
toward a more common solution with a more northwesterly track
overall. However, there is still enough difference between them to
put a bit of uncertainty especially into the Kodiak region.

&&

.AVIATION...
PANC...VFR conditions and northerly winds will persist through
Monday.

&&

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

Clear and dry conditions will prevail across much of Southcentral
through Tuesday as a ridge over the interior and a trough over
the northeastern Gulf allow the northerly offshore flow to
persist. These winds will continue to ramp up through the favored
gaps and passes along the Southcentral coast tonight and remain
steady through Monday before a secondary increase on Tuesday ahead
of an advancing front. Winds are expected to top out around 50 to
60 mph with occasional higher gusts for Thompson Pass as colder
air spills into the Copper River Basin. Periods of blowing snow
are likely through the pass, which may reduce visibilities at
times. Occasional blowing snow is also possible around Whittier,
Valdez, and Seward through Monday. For the interior, temperatures
overnight will fall below zero by Monday morning due to the clear
skies and light winds. One exception to the clearing conditions
will be the Copper River Basin as some scattered cloud cover and
isolated snow showers will linger through the through early
morning Monday.

For Kodiak Island, a deepening low in the western Gulf will swing
a front toward the region. This system will bring strong
northeasterly winds and snow to the Island beginning Monday
afternoon. The snow will quickly increase in intensity by late
in the afternoon, with blowing snow likely due to winds gusts
near 50 mph at times. The snow is then expected to mix with and
change to rain by late Tuesday morning as warmer air moves in. 6
to 10 inches of snow is possible over the Island, with the
potential for an additional half inch of rain following the
snowfall. There is still a fair bit of uncertainty surrounding the
evolution of this system, so stay tuned for updates. A Winter
Weather Advisory has been issued for this event.

Tuesday night the front across the western Gulf to Prince William
Sound and the Northeast Gulf stalls through Wednesday bringing
rain and snow across the Gulf with mainly all snow along the
coasts. Temperatures at the surface modify close to freezing along
the coasts during this time, so there is still some uncertainty
on precipitation type. Western Prince William Sound and the
eastern Kenai will receive the highest precipitation totals with
this system. Gusty winds along the front will persist through
Wednesday afternoon then taper down by Wednesday evening as the
front diminishes. This front could bring another round of intense
blowing snow, especially to Thompson Pass.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 and 2)...

Upper ridging with an arctic high to the north will keep quiescent
weather in place across Southwest through tomorrow. Winds will
increase from the northeast as a front over the Aleutian Chain
lifts north and increases the pressure gradient. Wind chills will
drop into the -25 range across the Kusko Delta, but will be well
warmer than wind chill advisory criteria. That same front will
bring snow and some blowing snow to the Alaska Peninsula on Monday
night and Tuesday.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 and 2)...

Two storm force lows over the next two days will impact the
eastern Aleutians with snow and blowing snow. Accumulations are
expected to be in the 8+ inch range for Dutch Harbor and 3-6"
over the next 2.5 days. However, accumulations will not be rapid
and it will be a wetter snow. Even so, we still expect some
blowing and drifting is likely given the easterly winds as high as
45-55 mph. Lighter snow showers and lighter winds will spread all
the way to the Central and Western Aleutians.

&&

.MARINE (Days 3 through 5: Wednesday through Friday)...

Bering and Aleutians...

A relatively quiet period is expected for the second half of the
workweek. Northeasterly gales will be ongoing Wednesday morning
across the offshore waters of the Bering west of St Matthew Island
and the Pribilofs. The winds will rapidly diminish Wednesday
night. No gales are expected anywhere on Thursday. A strengthening
North Pacific low will approach the Central and Western Aleutians
Friday afternoon and evening. This will cause widespread easterly
gales across the islands. The gale force winds will spread north
and east over much of the rest of the Bering as the low continues
to strengthen Friday night. Large differences in the models on
where and how strong the low will be Friday night make going into
any detail beyond that imprudent.

Western Gulf of Alaska...

A weakening low over Kodiak Island Wednesday morning may be
continuing to produce a few isolated gales in the windier spots,
but winds will quickly diminish below gale force by noon. A North
Pacific low will move into the eastern Gulf Thursday morning, but
with the strongest winds expected south and east of the low
center, only very isolated gales west of the low center are
possible briefly Thursday morning. No gales are expected elsewhere
in the Western Gulf through Friday.

&&

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

A relatively quiet start to the long-term forecast period will
turn much more active towards the weekend. A broad weak trough of
low pressure stretching from Southwest Alaska to west of Adak and
everywhere between will be in place Wednesday morning. This will
keep strong northeasterly winds bringing cold air southwestward
across the western Bering. Meanwhile southerly onshore flow across
the Gulf will keep the weather relatively warm and unsettled with
widespread snow shower activity, especially along the coast of
Southcentral.

The broad trough will shrink and shift eastward by Thursday,
allowing the winds across the Bering to relax. Clouds and
scattered snow showers will persist across the southern mainland,
but none of that activity will be organized or hazardous. The
surface low will shift to Prince William Sound on Friday, but once
again, with everything really weak, light winds and scattered snow
showers will persist in Southcentral. High pressure builds across
Southwest Alaska and the eastern Bering. That high will push east
into Southcentral by Saturday.

A strong North Pacific low will move into the western and central
Aleutians Friday afternoon and evening. This low will be the
catalyst for a return to strong winds, lots of clouds and
precipitation, and warmer temperatures by Sunday. The low will
track northeastward into the Bering on Saturday, with a lot of
disagreement on where it tracks on Sunday. There is much better
agreement that its leading front will spread north across all of
the southern mainland this weekend, reaching Southwest Alaska late
in the day on Saturday, then spreading eastward from there.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...Winter Weather Advisory 171.
MARINE...Storm Warning 131 132 136 138 352 150 172 174
		 Gale Warning 119 120 121 127 128 130 137 139 351 155-171 173
					  176 178 414
		 Heavy Freezing Spray Warning 119 121 127 129 139
FIRE WEATHER...NONE.

&&

SYNOPSIS AND MODEL DISCUSSION...EZ
SOUTHCENTRAL ALASKA...TM
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...JA
MARINE/LONG TERM...JW