Small Craft Advisory 241, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
409 PM AKDT Thu Mar 12 2020

.ANALYSIS AND UPPER LEVELS...
There is an upper level high over the eastern Bering and southern
Alaska, centered over the Alaska Peninsula. This high is moving
eastward. There is an upper low south of the eastern Aleutians,
pushing moisture northwards as the high moves away from that area.
Further west there is a strong stretching north from the western
Aleutians across the Bering to just west of the Bering Strait. A
strong surface high is draped across southern Alaska (near 1053 mb
in the Copper River basin), with offshore flow into the Gulf. This
is keeping the southern Mainland rather dry, with just some high
and mid level clouds at times and no precipitation.

&&

.MODEL DISCUSSION...
The numerical models continue to be in very good agreement. The
high resolution models are preferred due to the better handling of
gap winds. Forecast confidence is above normal.

&&

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

&&

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

Gradient winds in Prince William Sound, Thompson Pass, and the
Copper River Delta will slowly taper off through the nighttime
hours with the strong upper level high building across the
western Gulf of Alaska. Calmer conditions are expected beginning
Friday, lasting through the weekend.

Mainly clear and dry conditions will persist as high pressure
builds overhead Friday and Saturday over Southcentral Alaska.
With ridging in place, the strong northerly flow responsible for
the intrusion of arctic air will shut off as a weak southerly flow
develops, especially over the western half of Southcentral. This
blocking high will allow for a gradual warming trend through the
weekend with daytime temperatures climbing to around or slightly
above normal. Expectations are for carbon copy forecast days
Saturday and Sunday.

&&

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

Weather for Southwest Alaska will remain quiet for the next few
days. This is due to an entrenched area of high pressure over the
region. A frontal system will push up against this high, mainly
located out in the central Bering. However, this front will
stretch over the top of the high and will manage to make it over
Nunivak Island and right along the coast of zone 155. Warming
temperatures over the region will make it possible for some
freezing rain over Nunivak Island and the coastline tomorrow into
tomorrow night. The threat is low for freezing precip and this
forecast will need to be watched. Otherwise, quiet weather will be
present for the region the next few days. Outside of freezing
precipitation, confidence is high with this forecast.

&&

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

A frontal system currently located over the western Aleutians will
slowly work its way east the next day or so. Along this front,
strong southerly winds will create gusty winds through bays and
passes for the central Aleutians. This system will slowly progress
east until tomorrow, when it runs into high pressure to its east
over Southwest AK. This high pressure system will keep weather
quiet in the eastern Bering, while it stalls the front over the
central Bering. This means we can expect an inundation of moisture
and warming temperatures over the Central Bering the next few
days. This will cause steady rain for the central Aleutians. We
are confident in this forecast.

&&

.MARINE (Days 3 through 5 Sun through Tue)...
A low near the eastern Aleutians on Sunday will produce near gale
force winds, which will diminish Sunday night as the low weakens
and moves south. A front in the western Aleutians and western
Bering Sunday into Monday could produce gale force southerly
winds. A stronger front is expected in the western And Central
Aleutians on Tuesday, but the timing and strength of this system
is still uncertain.

&&

.LONG TERM FORECAST (Days 4 through 7 Mon through Thu)...
The forecast period begins on Monday with an upper level ridge
and surface high over the northern Gulf of Alaska extending into
the southern mainland and eastern Bering Sea. A storm system
near the central and eastern Aleutians is forecast to weaken and
slide northeast, reaching Southwest Alaska on Tuesday. This system
will then "top the ridge" on Wednesday and drop into the far
eastern Gulf or the Alaska Peninsula. The ridge will then push
back into southern Alaska, sliding east Wednesday and Thursday.
This will open up southwesterly flow aloft over southern Alaska,
bringing good chances of precipitation to the entire area.
Temperatures across southern Alaska will also warm through the
period, with above normal temperatures expected in Southwest
Alaska through the period, and above normal across Southcentral
by mid-week.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...Gales 165 170 172 185 412.
FIRE WEATHER...NONE.

&&

SYNOPSIS AND MODEL DISCUSSION...BL
SOUTHCENTRAL ALASKA...LB
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...BB
MARINE/LONG TERM...BL