Small Craft Advisory 292, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
434 PM AKDT Mon Mar 30 2020

.ANALYSIS AND UPPER LEVELS...
A strong closed upper level ridge is progressing eastward across
northern Alaska. An upper trough, with multiple embedded closed
lows, is centered over the Gulf of Alaska and Southeast Alaska
and very slowly progressing south and east. Southcentral is
positioned between the ridge and trough. Strong subsidence from
the ridge combined with a jet streak aloft, and tight surface and
thermal gradients continues to produce locally strong and gusty
winds through mountains gaps. Of particular note, the Matanuska
Valley has seen a long duration of strong winds (gusting to around
60 mph). Reports from the public and NWS employees indicate
power outages, downed trees, and damaged roofs. Winds across the
region have peaked and most of the forcing mechanisms have begun
to weaken, so expect a downward trend in the strength of these
winds.

Meanwhile, a north-south oriented cold front just east of the
Pribilof Islands is weakening as it continues its eastward March.
A triple point low has developed just south of the Eastern Aleutians
and it is tracking eastward toward the southern Alaska Peninsula.
Precipitation is falling as primarily snow ahead of the cold
front, with rain in Dutch Harbor and vicinity of the surface low.
Lastly, a weak low is passing south of the western Aleutians with
little or impact on the islands.

&&

.MODEL DISCUSSION...
Models are in much better agreement with the track of a triple
point low to around Kuskokwim Bay on Wednesday along with the front
hanging up west of the Alaska and Aleutian Ranges Wednesday
night. Will adjust the forecast for Southwest Alaska heavily based
on this latest guidance. Models are also now in agreement with
storm system tracking across the western Bering on Wednesday. Thus
overall forecast confidence for the next few days is above
average.

&&

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

&&

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

Bering Sea/Aleutians...
Beginning Wednesday, a low will transit the far western to
northern Bering Sea, with a trailing front extending down to the
southern Bering. The forecast advertises a large area of small
craft winds, though there is potential for an area of gales,
particularly over the Bering offshore area. Forecast confidence
then drops significantly with the track of the next storm Thursday
night through Saturday. It does look like this second storm will
be quite a bit stronger, so expect an increased likelihood of gale
force winds (and perhaps even a small area of storm force winds).
The western Bering and Aleutians look like they will bear the
brunt of this storm, but won't really know that until have a
better idea of where it will track.

Gulf of Alaska...
For the Gulf, it looks like another round of cold air advection
across the Alaska Peninsula and into the western Gulf beginning
Thursday night or Friday. Confidence in timing and strength is
low, but there is potential for gale to storm force gusts along
the Alaska Peninsula and Kodiak Island coastal waters.

&&

.LONG TERM FORECAST (Days 4 through 7/Friday through Monday)...
The upper level flow looks to be zonal through the extended
period, with the jet centered roughly from the Aleutian chain
and southern Bering eastward to the Gulf of Alaska. Expect fast
moving, generally "weakish" type storm systems. As would be
expected in such a flow, model guidance is a mess with little
agreement in track and timing of individual storms or features.
Thus, overall forecast confidence is low. The one thing that can
be said with some confidence is that with the southern extent of
the storm track, cold air remain ensconced over mainland Alaska.
As a result, temperatures will remain on the "cool" side, with
many areas at or below normal temperatures for this time of year.
Also, precipitation type will remain primarily in the form of snow.

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

An upper level trough over Southcentral moves to the east,
reaching the Alaska Panhandle by Tuesday night. Gusty outflow
winds that have been in place for most of the weekend will
eventually diminish by this evening. Generally quiet conditions
will persist across Southcentral through early Wednesday. A
weakening front will arrive from the west by Wednesday afternoon,
bringing increasing chances for precipitation to Southcentral by
the end of the week. Otherwise, clear and calm conditions are
expected through midweek.

&&

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

A front beginning to move into the Kuskokwim Delta coast this
afternoon will cause snow showers to develop this evening, but the
front quickly weakens by Tuesday morning. A low moving north out
of the North Pacific Tuesday night is forecast to track just a bit
further east, over or near Cape Newenham on Wednesday morning,
then north into the Kuskokwim Delta and western Alaska. This
slightly further east track will have several impacts. Around
Dillingham, this will allow the colder/drier air behind the low to
get a bit further east, diminishing snowfall totals overnight.
Thus, a combination of the lower amounts of precipitation and low
snow ratios will result in lower snowfall amounts in that area.
However, the more eastward track will also cause the low to
interact with the Kuskokwim Mountains more. A weaker low will be
less effective at downsloping and increasing the gap winds through
the Alaska Range, particularly around King Salmon and Iliamna.
Thus, temperatures have been lowered a bit, mainly for the
Wednesday night time period, so several inches of snow are
probable now in those regions too. The trailing front will stall
out over Southwest Alaska into Thursday, only gradually moving
east ahead of another front moving into the Kuskokwim Delta. This
second front will have considerably less moisture to work with, so
snowfall totals with the second front will be lighter.

&&

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

A front over the eastern Bering will move into Southwest Alaska
tonight and dissipate. A low develops along the front south of
Dutch Harbor tonight, which will lift northward to near Cape
Newenham Wednesday morning, then into mainland Alaska. Impacts
from this low will primarily be felt over Southwest Alaska. A low
will move over the northern Bering on Thursday morning, with some
potential for areas of gale force winds across the waters around
Saint Matthew Island. A much stronger front moves into the western
Aleutians during the day on Thursday. Gale force winds and high
seas are possible with that feature as well.

&&

.MARINE (Days 3 through 5/Wednesday through Friday)...

Bering Sea and Aleutians...
On Wednesday, there is better model agreement today with the
front entering the northwestern Bering. Winds are forecasted below
gale force at this time, but there will likely be gale force
winds and widespread precipitation accompanying this system that
is showing a stronger signal than yesterday's model runs. Thus,
confidence is improving in the track and intensity of this low.
Impacts of this in the eastern Bering are minimal as the front is
expected to dissipate before reaching that area through Thursday.

Gulf of Alaska...
There is a chance of small craft southeasterly winds across the
western Gulf on Wednesday associated with a low over Bristol Bay.
Confidence in these small craft winds is low as there are
significant differences in solutions for the low track and
intensity. For Thursday there is low confidence in the wind
forecast, though the weather pattern is expected to remain benign.

&&

.LONG TERM FORECAST (Days 3 through 7/Wednesday through
Sunday)...

Guidance is consistent with an upper level ridge extending across
the Alaskan mainland on Wednesday as an upper trough is present
over the Bering/Aleutians. Due to this, temperatures will be
warmer with a benign weather pattern over the Alaskan mainland and
cooler with a more active weather pattern over the Bering/Aleutians.
Uncertainty increases into Thursday as guidance shows a higher
degree of variation in solutions with upper level synoptic features
which will affect the placement and intensity of surface synoptic
features. The only area of consistency is the upper level ridging
will continue over the eastern Alaskan mainland near the AlCan
border and thus, expect warm temperatures and quiet weather for
that region. Very low forecast confidence exists overall Friday
through Sunday as major differences in upper level synoptic
features exist between guidance which is causing significant
differences in the placement of surface features causing a high
degree of uncertainty in the forecast.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...High Wind Warning 111.
MARINE...Gale
		 Heavy Freezing Spray 160
FIRE WEATHER...NONE.

&&

SYNOPSIS AND MODEL DISCUSSION...SEB
SOUTHCENTRAL ALASKA...KO
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...JW
MARINE/LONG TERM...SEB