Small Craft Advisory 417, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
457 PM AKDT Mon May 18 2020

.ANALYSIS AND UPPER LEVELS...
The main low is churning in the Bering Sea northeast of Adak this
afternoon with an occluded front associated with it in the
northern Bering Sea stretching into the Gulf of Alaska. A triple
point on the front is near Kodiak Island and moving north-
northwest. This front is stronger in the Gulf of Alaska and will
bring a barrier jet along the north Gulf cast as it moves into
that area.

&&

.MODEL DISCUSSION...

Models remain in good synoptic agreement through the week. Main
model concerns are still with more localized details such as gap
winds. Precipitation amounts on the models are in better agreement
than the previous run of models as well.

&&

.AVIATION...
PANC...Southeast Turnagain Arm winds are expected to develop by
late afternoon and persist through the evening. These winds should
diminish overnight. Rain showers will be in the area this evening
through overnight, but VFR conditions are expected.

&&

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

A front associated with a triple point low spinning up in the
eastern Bering will remain across the Barren Islands this evening.
This will bring increasing winds to the area and chances for rain
across coastal locations from Kodiak to Cordova. Rainfall
potential for Anchorage seems to be limited as we look to
downslope, preventing rain from reaching the area. As the front
moves northward through tomorrow, it will weaken, and winds will
diminish and chances for precipitation will lower. The forecasted
area should completely dry out Wednesday as high pressure
overtakes the Gulf. Looking ahead to Thursday, we seem to repeat
the pattern that started day one. Another front will move into
the southwestern Gulf where rain and winds will increase for the
aforementioned areas.

&&

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

A front moving into Southwest Alaska is causing widespread light
rainfall across Bristol Bay and the coast of the Kuskokwim Delta.
The rain will be most persistent across Bristol Bay as a low near
Shelikof Strait tracks northward. The entire complex fizzles out
and dissipates into Tuesday, which will generally lead to plenty
of lingering moisture and scattered shower activity. There will be
a brief break Tuesday night into Wednesday, where some portions of
the area will clear back to partly cloudy skies. However, the dry
weather will be short lived as another front moves into Southwest
Alaska Wednesday afternoon and evening. This second front will be
stronger than the current one, so downsloping and stronger gap
flows are expected into Thursday as the front moves inland. With
another round of rain and wind moving in Wednesday, expect that
temperatures will remain at or below normal with negligible fire
weather concerns.

&&

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

A strong North Pacific low will move into the Western Aleutians
tonight. Over the next few days, the low will occlude, become
vertically stacked, and slow to a crawl as far as forward movement
is concerned. By late in the day Thursday, the low will be over
the Central Bering. Gale force winds in the cooler air behind the
low are expected, along with gales across the central and eastern
Aleutians as the leading front moves through Tuesday and Tuesday
night. The low grows in size and stalls out, so associated
unsettled weather will persist through Thursday.

&&

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

Gulf of Alaska: There is high confidence that a frontal system
will slowly pass through the Gulf from southwest to northeast
throughout the time period. Accompanying this frontal system will
be an area of small craft advisory winds and waves as the front
moves through. Another low is expected to form along the front
early Saturday which will keep the region unsettled through the
first half of the weekend.

Bering Sea: A low pressure system will meander its way through
the Bering Thursday through Saturday while slowly weakening which
will keep the Bering unsettled. During this timeframe, winds are
expected to remain below gale force winds with small craft
advisory winds the main strength with waves accompanying them. The
main differences are the exact placement of the low but guidance
remains in fairly good agreement on the strength leading to above
average confidence.

&&

.LONG TERM FORECAST (Days 4 through 7: Friday through Tuesday)...

The long term period looks quite unsettled for the Bering
Sea/Aleutian Chain and Southwest Alaska. A complex low is
expected to meander in the Bering the duration of the forecast
period keeping the weather unsettled. Differences between model
guidance emerge with the strength of the ridge over the AlCAN
border northwest to the North Slope of Alaska. Depending on the
strength of the ridge, multiple upper level waves of energy may
rotate around the low in the Bering. A stronger ridge will help to
suppress the fronts/upper level waves to the immediate coastline
while a weaker ridge would allow for these waves to penetrate
further inland.

With this pattern in place, cooler temperatures and increased
winds are expected through the period especially for Southwest
Alaska and the Aleutian Chain, and Pribilofs. For Southcentral,
the forecast for temperatures becomes a little more tricky as
it depends on how strong the upper level ridge is. The Copper
River Basin is where temperatures may still be above average as
the upper level ridge would have the best hold there. As a result,
forecast confidence is average for this period.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...Gales 172-176 178 411 413.
FIRE WEATHER...NONE.

&&

SYNOPSIS AND MODEL DISCUSSION...EZ
SOUTHCENTRAL ALASKA...CK
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...JW
MARINE/LONG TERM...MV