Small Craft Advisory 287, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
405 AM AKDT Sun Mar 29 2020

.ANALYSIS AND UPPER LEVELS...
A 987mb low was observed over the Gulf of Alaska moving rapidly
off to the southeast and away from Southcentral Alaska this
morning. Surface high pressure is building in behind this low
pressure across Southcentral with a cold air mass moving in.
Strong gusty winds are being observed across the Matanuska Valley
this morning due to a tight pressure gradient in place due to
building surface high pressure inland and the departing low over
the Gulf. Winds were also gusting as high as 50-55 mph this
morning at Thompson Pass.

Cold northwesterly winds are bringing gusty winds to the normal
gaps and passes in the area of the AKPEN this morning as cold air
advection continues this morning. Upslope flow against the
mountains is also allowing for some snow showers across the higher
elevations and peaks.

A front was observed moving across the western Bering and
Aleutians bringing rain showers to that part of the Aleutian
Chain.

&&

.MODEL DISCUSSION...
Models are in good agreement through Monday night.

&&

.AVIATION...
PANC...VFR conditions with gusty northerly winds through the
TAF period.

&&

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

Strong offshore flow and gap winds will be the main story through
Monday. The synoptic setup: an upper ridge building east across
the mainland setting up favorable northerly flow aloft, cold
advection in the lower elevations, and strengthening thermal and
pressure gradients across Southcentral. This will result in
generally brisk offshore and gap flows in many areas. The
strongest of these flows are expected in the Thompson Pass/Valdez
area, Copper River Delta, and the Matanuska Valley where winds are
expected to hit warning levels of around 75 mph. These conditions
are expected to develop this morning as a fairly strong short
wave drops south across the area. This will be followed by
increasing northerly jet support as the upper ridge builds east.
Warning level winds are expected to continue into Monday afternoon
before diminishing.

&&

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

A quieter pattern will move into Southwest Alaska as high pressure
begins to build across the region today after the snowfall that
was seen the past few days. Clear skies in this pattern will help
daytime temperatures for most areas reach the mid-20s today and
Monday, with cloud-free conditions bringing low temperatures into
the single digits for the next two nights.

By Tuesday morning, a weakening front over the eastern Bering
will approach the Southwest coast, with the potential for scattered
snow shower activity along the Kuskokwim Delta Coast. Little snow
accumulation is expected with this system.

&&

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

Heavy freezing spray will persists this morning over the eastern
Bering as strong winds continue. Areas south of the eastern
Aleutians and AKPEN can expect gusty winds through gap areas to
calm down heading into this afternoon as the associated low
systems moves out of the forecast area.

A front over the western Bering will strengthen as it moves into
the eastern Bering for this afternoon. Gale force winds will
persists with this system through Monday morning, when it begins
to weaken and lift into the northern Bering. Widespread
precipitation is expected with this system with snow eventually
transitioning to rain across the Aleutians. The Pribilofs will
remain just below freezing, so they should stay all snowfall as
the front passes over them on Monday, with the potential for
possible blowing snow. However, if their temperature do warm above
freezing, they could see a mix of rain or snow, or all rain.

&&

.MARINE (Days 3 through 5/Sunday through Tuesday)...

Bering Sea/Aleutians...
A storm system will track across the western to central Bering on
Sunday. There is uncertainty in the exact track of the low center,
but high confidence in widespread small craft winds with gales
likely near the low center. The eastern Bering will likely see
minimal impacts from this, as most model solutions track the low
to the northern Bering, or even into Russia. Forecast confidence
for Monday/Tuesday drops significantly, although it doesn't look
like any major storm systems will affect the region.

Gulf of Alaska...
There is a high confidence in gap winds along the Gulf coast on
Sunday. These will diminish by Monday and the overall weather
pattern looks quiet.

&&

.LONG TERM FORECAST (Days 4 through 7/Monday through Friday)...

Guidance is consistent with the overall synoptic pattern on Sunday
with an upper level trough over the Alaska mainland while upper
level ridging slowly moves eastward across the central and eastern
Bering. This will result in cold temperatures across the
mainland. A high confidence exists with a warming trend in
temperatures across the Alaska mainland in particular Southwest
Alaska Sunday through Tuesday. However, there is low confidence
with respect to the magnitude of the expected warm up as there are
discrepancies between guidance with how fast this ridge is
moving. The GFS appears to have the fastest bias as the GEM and
ECMWF show the upper trough extending into the Ahklun Mountains
while the GFS has the trough only extending to the eastern AKPEN.
More significant differences between guidance arise on Wednesday
with respect to the amplitude of the upper ridge over Southcentral
Alaska. This means that there is a low confidence in the
temperature forecast as the placement of this upper ridge affects
the placement of the surface ridging and thus causing major
discrepancies in the temperature forecast. One area of confidence
for this period is the weather is expected to remain benign across
Southcentral during this time as high pressure will be over the
area. Significant discrepancies continue on Thursday and Friday
and thus the forecast confidence remains very low for this period
at this time.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...High wind warning 111 and 131.
MARINE...Gales 127 130 131 185 411-413.
FIRE WEATHER...NONE.

&&

SYNOPSIS AND MODEL DISCUSSION...MV
SOUTHCENTRAL ALASKA...RMC
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...AH
MARINE/LONG TERM...ED