Small Craft Advisory 124, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
530 AM AKST Thu Feb 6 2020

.ANALYSIS AND UPPER LEVELS...

An upper-level trough and associated weak surface low over Prince
William Sound is producing areas of light snow and low stratus
over the Copper River Basin. Along the immediate coast, a low-
level southerly flow has advected enough warmer, marine air to
push temperatures a couple of degrees above freezing. This has led
to a mix of rain and snow for areas like Cordova and Valdez
overnight. Elsewhere across Southcentral, light snow and low cloud
cover persists from Anchorage north to Talkeetna and Skwentna.
This is due to an upper-level trough lifting northeast across Cook
Inlet this morning. Weak ridging behind the trough has ushered in
clearer and drier conditions for the southern half of the Kenai
Peninsula, Kodiak Island, and portions of the Alaska Peninsula.

A surface front draped across the interior of Alaska is separating
milder air across Bristol Bay from arctic air moving south across
the Y-K Delta this morning. Temperatures from Bethel north and
west are in the single digits to below zero while south and east
temperatures are in the upper teens to near 30 degrees. Light snow
is also falling across the Kuskowim Delta along the front.

For the Bering and Aleutians, an upper-level low is situated over
the central Bering. At the surface, a complex low with multiple
centers of circulation is centered just north of Atka this
morning. One center of circulation is southwest of the Pribilofs
and is bringing occasional snow and easterly wind gusts to the
islands. A second is east of Atka and a third is north of Adak.
The low near Adak is producing northwesterly gales and snow across
portions of the western Aleutians. Yet another low is south of
Dutch Harbor and is producing some rain and southerly winds across
the eastern half of the Chain and far southern AKPEN.

&&

.MODEL DISCUSSION...
The numerical models are in fairly good agreement with the overall
synoptic-scale pattern into the weekend. The larger differences
are with the placement and strength of the various lows forming
the complex low system currently over the central Aleutians and
AKPEN through early Friday. However, given the model spread, the
resultant weather impacts remain fairly similar. Thus, the
forecast confidence is above average. The NAM and NAMnest were
favored, especially for winds over the Southern Mainland, given
the higher resolution.

&&

.AVIATION...
PANC...General MVFR conditions are expected through Thursday
morning, mainly for lower ceilings. Some light snow is still
possible early this morning, but is not expected to significantly
reduce visibility. Southerly winds have developed across the
terminal overnight and are expected to continue through Thursday
evening. MVFR ceilings are expected to return Thursday night with
the potential for fog in the vicinity of the airport complex. IFR
visibility is possible for a time Thursday night if fog does
moves over the terminal.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 and 2)...
Light snow rapidly diminishes this morning as the front and
associated trough moves northeast and dissipates. Short wave
ridging gives a pause in the weather today with clouds scattering
across much of Southcentral this afternoon. The next front moves
to Kodiak Island this evening, taking a northward track overnight.
Precipitation will spread across the gulf and eastern areas of
the Kenai through midnight and then afterwards to Prince William
Sound and the northeast Gulf coasts. Light rain is expected over
the Gulf with mainly snow along the coasts and inland locations.
The surface low driving this front rapidly fills by Friday
afternoon.

A strong storm system develops Friday and pushes yet another
front to Kodiak Island Friday evening. This front will be a
powerful system that impacts Southcentral through Saturday night.
Strong gusty winds increase Friday evening for the Western Gulf
and then increase for the Kenai Peninsula late Friday night. This
system should be monitored for updates as stronger winds are
anticipated through channeled terrain. Snow amounts are also being
monitored across the southern Copper River Valley as there is
still some uncertainty on how quickly the cold pool erodes at the
surface.

&&

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

A weakening low over Southwest mainland will keep snow showers in
the forecast this morning across the Y-K Delta and Kuskokwim
Valley, which will taper off through late morning. A shortwave
ridge building in over interior Bristol Bay this morning will keep
low stratus and dry conditions early today. The next round of
precipitation moves in near Dillingham this afternoon and shifting
northeastward tonight associated with a surface low moving over
the AKPEN throughout the day. There is still uncertainty in the
exact track of this low as it moves eastward through Friday
afternoon. Dry conditions will persist across the Kuskokwim Delta
tonight as gusty winds and colder air move into the area. A Wind
Chill Advisory remains in effect from Hooper Bay to Kipnuk, where
there will be the coldest advection.

The pattern will then shift Friday evening when a warm front moves
across the AKPEN into Southwest Alaska. The biggest forecast
challenge is how far north this system will travel. However,
widespread precipitation is expected as it moves farther inland
overnight Friday into Saturday. With gusty conditions still in
place across the Y-K Delta, blowing snow is a forecast concern as
precipitation begins to move inland Friday night and through
Saturday.

&&

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

An active pattern remains across the Bering Sea and Aleutians
today. A complex low over the central Bering will progress
eastward, shifting its energy to a low developing over Cold Bay
this afternoon. A small area of gale force winds will accompany
the low as it tracks over the AKPEN overnight tonight.

Over the central Aleutians, models are in better agreement today with
a storm force low that will move between Adak and Dutch Harbor by
Friday afternoon. There is some model discrepancy as the low
tracks eastward, but strong winds and widespread precipitation
will accompany this storm.

To the west, models are still tracking a strong storm system that
will begin to move over the western Aleutians and Bering Friday
afternoon. The biggest question of uncertainty is whether a low
will develop near Shemya (NAM solution) from the storm-force parent
low that remains southwest of the forecast area. The GFS/EC
solution was favored for this forecast package, keeping widespread
gale force winds stretched across the central and western Bering
and Aleutians Friday and Saturday. However, storm force wind gusts
are still likely.

&&

.MARINE (Days 3 through 5: Saturday through Monday)...

Gulf of Alaska:

A strong low will be in the eastern Bering Sea with a front
extending across the Gulf of Alaska Friday. This low and front
will likely support gale force winds across the Gulf of Alaska,
Kodiak Island Waters and the North Gulf Coast Saturday. The lows
and gradient weaken Sunday and wind across the Gulf of Alaska,
Kodiak Island and south central Alaska coastal waters will remain
below gale force Sunday and Monday.

Bering Sea/Aleutians:

Beginning Friday night, storm force winds will move over the
waters south of the Aleutians and track eastwards. By Saturday,
the winds north of the AK Pen will strengthen to storm force as
well. This storm is expected to weaken rapidly during the day on
Saturday and by Sunday, winds will weaken to gales or lighter
across the area. Late Sunday, a new storm in the western Aleutians
will bring gale force winds, but these will remain west of Atka
and continue to weaken through Monday.

&&

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

Active weather remains on tap for the southern mainland and
Kodiak Island through the long term Saturday through Wednesday.
Strong low pressure over the eastern bering Sea supports a strong
gradient across SouthCentral Alaska Saturday along with an influx
of warm moist air. This will bring above normal temperatures to
the region along with strong winds, especially across the coastal
mountains, that will support Chinook-like conditions. Continuing
through the weekend there will be a strong southwest flow. An
upper level ridge then pushes into western Alaska and builds over
the mainland through Tuesday to then have a strong upper level
trough push into the mainland Wednesday. At the surface the models
are not in great agreement, thus the confidence in the longer
term forecast is not high and will reflect the expected trends of
the weather for Monday through Wednesday.

In the west, the first concern is the storm moving through the
region on Saturday. There is some warm air associated with this
system, but that looks like it will remain over Bristol Bay and
the Upper Kuskokwim Valley. Meanwhile, northerly winds to the west
will bring plenty of cold air down over the Kuskokwim Delta.
Residents in this area should be on the lookout for traditional
wintry weather with winds and snow reducing visibility along the
coast. By Sunday this system will weaken dramatically as it moves
northeastward and relatively quiet conditions will begin the week.
As we move into Tuesday and Wednesday, the model forecasts begin
to differ greatly. GFS indicates a strengthening low in the
central Aleutians, but other model solutions indicate a weaker low
moving through the Bering. Therefore, confidence is low on timing
and strength of weather systems moving through western Alaska
through the middle of next week.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...Wind Chill Advisory 155.
MARINE...Heavy Freezing Spray Warning 179 185 411 412 414.
		 Gale Warning 155 170 172>174 178 179 185 411>414.
FIRE WEATHER...NONE.

&&

SYNOPSIS AND MODEL DISCUSSION...TM
SOUTHCENTRAL ALASKA...KH
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...AH
MARINE/LONG TERM...LF/SA