Small Craft Advisory 337, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
420 AM AKDT Tue Apr 14 2020

.ANALYSIS AND UPPER LEVELS...

A weak, vertically stacked low is located north of Adak. Warm,
southerly flow ahead of it is bringing scattered showers to the
Bering/Aleutians and Alaska Peninsula. Per water vapor imagery,
this moisture originates from near Hawaii. Farther east, a
negatively titled upper level trough encompasses much of mainland
Alaska, leading to patchy fog this morning as indicated on current
satellite. Otherwise, conditions will remain benign with
increasing clouds through the day.

&&

.MODEL DISCUSSION...

Models remain in good agreement through the end of the week.
Generally southerly flow aloft will lead to a warm, wet pattern
for the foreseeable future. The timing of the next front moving
over Southcentral mid-to-late week continues to get a bit slower.

&&

.AVIATION...

PANC...Intermittent patchy fog and/or low stratus is possible over
the terminal through the morning. Otherwise, light winds and VFR
ceilings will persist.

&&

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

The upper level ridge building over Southcentral Alaska today is
a little bit stronger than it looked earlier. This is having a
couple of impacts to the forecast. The first is that is has
basically washed out the upper level wave that had been expected
to move northward up Cook Inlet later today. This wave is weak and
even a little farther west so even the chance of rain for Kenai
and northward later today has been lessened. This ridge will push
most temperatures near sea level well into the 40s again today
with a few temperatures reaching 50 possible both this afternoon
and Wednesday.

By late Wednesday afternoon, the ridge will have shifted slightly
eastward which will allow a front to move into Southcentral and
bring in rainfall for Wednesday night into Thursday for much of
the area. Kodiak and the north Gulf coast will see the rain begin
tonight. Temperatures will still be warm at this time and rain
will be the precipitation type for all highways and populated
areas with this system. The north Gulf coast, including the Prince
William Sound region, will likely see rain amounts of an inch or
more from tonight through Wednesday night as this front moves
through the region.

&&

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

An active weather pattern will persist across Southwest Alaska
through Thursday as a subtropical jet helps to keep a soggy
pattern as warm air and southerly flow move into the region.
Scattered showers along the Kuskokwim Delta and Bristol Bay will
continue this morning through this afternoon as the associated
surface low in the eastern Bering pushes northward out of the area
later today.

A much more organized swatch of moisture will move overnight
tonight into Wednesday as the next front lifts northward. This
warm system will keep a long period of rain in the forecast before
tapering off late Wednesday. Rainfall totals of around one half
inch to an inch are expected with highest totals around the
Bristol Bay region. By Thursday, things should quiet down with a
few showers lingering across the area before the next system
approaches the Southwest coast by the end of the week.

&&

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

As one low off the Kuskokwim Delta coast pushes northward out of
the forecast area this morning, the next system quickly begins to
move in over the eastern Aleutians and Alaska Peninsula by this
afternoon. Strong winds will accompany this system as it lifts
northward, as well high high rainfall totals between a half inch
to an inch between starting this afternoon lasting through early
Wednesday. The highest rainfall totals will be on the south side
of the eastern Aleutians and Alaska Peninsula extending from Cold
Bay and King Cove to Chignik. By Wednesday afternoon, this first
system will have moved into the Gulf and Southcentral Alaska.

Attention then quickly focuses on the next system that will begin
to move over the western and central Aleutians by Wednesday
afternoon into the evening. Small crafts to gale force winds will
accompany this system as it moves into the central Bering by
Wednesday night and continues to progress eastward over the
Pribilofs and eastern Bering for Thursday. Expect another round of
rainfall with this system, but rainfall totals are not expected to
be as significant with this second front as they are with system
moving in today.

&&

.MARINE (Days 3 through 5)...(Thursday through Saturday)

Gulf of Alaska...

Confidence remains high that a progressive weather pattern
will continue into the weekend. Thursday and Friday will see
winds generally remain sub gale, with a south to southwesterly
trajectory (8-10 ft seas). A weak barrier jet will form Wednesday
evening and decay Thursday along the Gulf Coast.

Bering Sea...

A gale force low south of Shemya will lift north into the Bering
by Friday afternoon. An attendant gale force weather front move
east along the Eastern Aleutians before weakening Friday.
Confidence remains high that all winds will remain below storm
force, and that the highest seas (20-22ft) should remain south of
the Aleutian Chain. High end northerly Gales are expected across
the extreme western Bering Saturday.

&&

.LONG TERM FORECAST (Days 4 through 7)...
(Wednesday through next Saturday)

Model guidance on the long term pattern remains in fairly good
agreement throughout the period. Guidance keeps the center of the
ridge over the Gulf of Alaska to the Alexander Archipelago
through the weekend. One final wave of energy is expected to ride
along the periphery of this ridge Friday into Saturday bringing
one more round of unsettled weather to Southwest and Southcentral
Alaska. With the northern part of the upper level ridge remaining
in place across Southcentral and Southwest Alaska, slightly above
to above normal temperatures will continue to be the theme
throughout the period. The only areas that may remain just cold
enough for snow or a rain/snow mix are: Lower Kuskokwim Valley and
the northern Susitna Valley with any chance for snow greatest
during the overnight. After this wave of energy passes through,
the upper level ridge is expected to build over the Bering and
Southwest Alaska. This will keep any storm systems away from the
region for Sunday and Monday bringing a return to quiet and dry
weather, though, remaining above normal temperature wise leading
to average confidence for the long term period.

Over the Bering and Aleutians, model guidance continues to show a
low pressure driving up through the Aleutians into the Bering and
then into Southwest Alaska Friday with the low dissipating heading
into Saturday. This will keep unsettled conditions across the
Bering for Friday/Friday night. Behind this system, model guidance
continues to show another storm system moving into the area south
of the Aleutian Chain Saturday. The main difference between the
GFS and ECMWF today is how far north or south the low will be with
the strength of the low coming into much better agreement. The GFS
is the farthest north with the storm and the ECMWF is further
south. This will play a role in how strong the winds get for the
Aleutian Chain and the offshore marine zones leading to average
confidence.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...Gale Warning: 130.
FIRE WEATHER...NONE.

&&

SYNOPSIS AND MODEL DISCUSSION...AP
SOUTHCENTRAL ALASKA...EZ
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...AH
MARINE/LONG TERM...SS/MV