Gale Warning 315, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
304 PM AKDT Tue Apr 23 2019

.ANALYSIS AND UPPER LEVELS...
The large resident upper low anchored over Bristol Bay continues
as the dominant weather feature. Broad cyclonic flow associated
with this system covers much of the Southern mainland and the
surrounding waters. Cold air aloft associated with the upper
center has destabilized the atmosphere and given rise to open
cellular cumulus clouds (showers) across much of the eastern
Bering Sea to over the North Gulf Coast. These can be seen on
satellite imagery cyclonically rotating around the upper center
over Bristol Bay. Additionally, numerous smaller waves embedded
in the upper flow can be seen rotating around the upper center.

&&

.MODEL DISCUSSION...
Models are in generally good agreement through Thursday
afternoon.

&&

.AVIATION...
PANC...VFR conditions and generally light winds will prevail
through the next 24 hours.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 and 2...Weds and
Thurs)...
Unstable conditions will linger over Southcentral and the
Northern Gulf overnight while cold temperatures associated with
the upper level low remain in place. This will bring scattered
showers throughout the night, although the primary areas of focus
will be the eastern Kenai Peninsula and the Prince William Sound.
Temperatures will remain fairly cool, with the cold air aloft, so
any precip that falls should fall as snow, but it is not expected
to accumulate.

Beginning Wednesday morning, a new low pressure system will
develop southwest of Kodiak and slowly traverse the Gulf of
Alaska. The front with this system is fairly weak, but
northeasterly winds around the low will increase through Shelikof
Strait. As the front approaches the north Gulf Coast, expect to
see winds pick up in the coastal marine zones to minimum gale
force. Precipitation will increase along the front, but warmer air
will begin to mix in and Prince William Sound and the coastal
areas will likely see a mix of rain and snow beginning Thursday.
The weather with this front will be mostly confined to the Gulf,
so most of Southcentral will remain dry and slowly warm as the end
of the week approaches.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 and 2)...
Scattered snow showers will continue to wane through the evening
hours tonight as an upper level low slowly slides southeast. Skies
will begin to clear across much of the area tomorrow and tomorrow
night, allowing for temperatures to dip into the teens overnight
but warm into the low to mid 40's Thursday afternoon.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 and 2)...
High pressure across the western Bering will slowly build and
slide east along the Aleutians through Thursday. Despite the ridge
overhead, expect the usual Bering Sea stratus to loom in the
vicinity and keep daytime temperatures moderated. Thursday night,
another weather system will move in from the Pacific and impact
the western Aleutians, bringing gales and rain to the area again.

&&

.MARINE (Days 3 through 5)...
A ridge in the east and central Bering Sea Thursday night will
keep the storm track in the Western Bering Sea through the end of
the week. The ridge will weaken over the weekend as the
persistent storm track edges a little farther to the east. Gales
are expected in the western Bering storm track with a chance of a
small area of storms in the far western Bering Sea Thursday night.
Gales may make it into the central and eastern Bering Sea as well
by Saturday night.

A low in the central Gulf of Alaska Thursday night will bring a
chance of Gales through early Friday though these gales are less
certain than the Bering Sea ones. Winds and seas will improve
early in the weekend as the old Bering Sea ridge moves over the
Gulf. However, a front may bring some gales back into the western
Gulf late Saturday night.

&&

.LONG TERM FORECAST (Days 3 through 7)...
Starting on Thursday night, the Bering Sea ridge will be in the
eastern Bering Sea and pushing into the Southwest mainland
Alaska. The Gulf of Alaska will have a low spinning around in it
which will move eastward by Friday leaving generally offshore
flow over southern mainland Alaska Friday. The one real item which
is not adequately resolved during that time frame is with an
upper level low on Friday night. The GFS model is insistent that,
as the low in the Gulf moves eastward, an upper level low will
develop over Southcentral and then move over Bristol Bay on
Sunday. Other models do not have this feature or at least not
nearly as strong. The GFS ensemble members show this feature is
being handled erratically by the GFS itself. The ensemble spaghetti
plot melts into an incomprehensible mess of lines that is
difficult to look at by Saturday night. This indicates the model
is unsure of this feature. Therefore we are downplaying its
effects through the weekend. However, if it does develop in all
the splendor shown by the GFS, it will bring in cooler and
cloudier weather to Southcentral Alaska as well as the chance of
snow showers mainly over higher elevations.

Past this weekend, it still looks likely that a blocking upper
level high will be able to move over the state bringing in warmer
weather, but we will have to keep an eye on developments the next
few days to see if this solution still seems favorable as the
time approaches.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...NONE.
FIRE WEATHER...NONE.

&&

SYNOPSIS AND MODEL DISCUSSION...RC
SOUTHCENTRAL ALASKA...LF
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...SS
MARINE/LONG TERM...EZ