Small Craft Advisory 387, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
449 AM AKDT Thu May 7 2020

.ANALYSIS AND UPPER LEVELS...
An upper level high remains present over the southern Mainland of
Alaska leading to mostly clear skies for Southcentral and partly
cloudy skies across Southwest Alaska. A weakening upper level wave
was seen propagating northwestward towards the Kenai Peninsula. In
association with this feature, increasing clouds were seen moving
towards Cordova along with a few rain showers riding along the
Gulf Coast.

Further south is where all the active weather is currently
occurring. A strong upper level low over the North Pacific near
50N 150W was seen slowly meandering northward. On the eastern
flank of this upper level low, a very deep moisture feed
(atmospheric river) was seen moving northward and then
northwestward across the Gulf of Alaska. Looking at ASCAT
scatterometer data, mainly small craft advisory level winds were
observed across the Gulf. Further south near 50N 140W, gale force
winds were observed moving northward with this moisture plume
towards the Gulf of Alaska. This major system will be the culprit that
brings Kodiak Island (including the city of Kodiak) a heavy
amount of rainfall as well as strong gusty northeasterly winds.
The same moisture plume will also affect the eastern Kenai
Peninsula and areas along Prince William Sound Thursday into
Friday as the system continues to meander over the North Pacific
and pushes its front northward.

Over the Bering Sea and Aleutian Chain a front was seen migrating
slowly eastward with extensive cloud cover and gusty
southwesterly winds observed over Shemya. The leading edge of this
front is where the precipitation in the form of rain was observed
at Atka. This front will continue moving east while dissipating
later Thursday as the energy with the system gets sheared apart
(frontolysis).

&&

.MODEL DISCUSSION...
Models remain in very good agreement over the next few days with
the synoptic features. As a result, forecast confidence remains
very high.

&&

.AVIATION...
PANC...VFR conditions will persist throughout the TAF period. On
Thursday, the Turnagain Arm wind will bend solidly southward as it
exits Turnagain Arm due to much lower pressure off to the south
in the Gulf. This usually means the winds will remain south of
the terminal. However, with sufficient heating and instability
inland over the Susitna Valley, periods of gusty southeasterly
winds are possible at the terminal Thursday afternoon and evening.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 and 2)...
The large low is approaching the southern Gulf of Alaska this
morning with the main front heading rapidly toward Kodiak Island.
Kodiak is the area that is expected to see the strongest winds and
heaviest rain from this low.

A strong upper level wave is embedded in the flow around the low
and will bring rain to the north Gulf coast today as well as
strong winds. This wave can best be seen on IR satellite
approaching the Cordova area from the southeast and is a distinct
feature from the main front in the southern Gulf of Alaska.

Gusty winds will increase through channeled terrain such as
Turnagain Arm today, but the low is remaining far enough south
that they will not get as strong as a low that traverses the
region. Inland areas will see little rainfall as downsloping will
keep rain relegated to the windward coastal side of the
mountains.

&&

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

A front associated with a low in the Gulf will lift inland today,
bringing gusty easterly winds to the Alaska Peninsula and greater
Bristol Bay area. Rain is expected across the eastern side of the
Alaska Peninsula, but strong midlevel winds will allow for
downsloping, keeping leeward areas mostly dry. As the low weakens,
winds will diminish by Friday morning. Temperatures are still
expected to warm through the end of the week with highs in the low
60s across most interior locations.

&&

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

A weakening front over the central Bering continues to slowly move
eastward this morning. By the evening, a strengthening low
approaches the western Aleutians, bringing gales and storm force
gusts to the western Bering Friday morning. This low will also
spread precipitation across the Chain, reaching the central
Aleutians and Pribilof Islands by Saturday morning. As the low
center lifts northward, the front will occlude and weaken
significantly over the eastern Bering Saturday afternoon. On the
backside of this low, colder air will fill in, bringing showery
conditions to the western Bering for the weekend.

&&

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

Bering Sea/Aleutians...
A strong low pressure system will be moving northeastward across
the western Bering/Aleutians on Saturday. There is increasing
confidence that widespread gale force south-southwesterly winds
associated with this low will develop late Friday night into early
Saturday morning across the western Bering/Aleutians. Confidence
also remains high with a second area of gale force southerly
winds developing in the central Bering/Aleutians on Saturday. As
the low gradually weakens while moving northeastward, there is
above average confidence that these gale force winds will ease
Saturday night into Sunday morning. A second low pressure system
is expected to approach the western Bering/Aleutians Monday
afternoon, though confidence in the wind forecast remains low as
there is a high degree of uncertainty in the intensity and
placement of this low.

Gulf of Alaska...
Forecast confidence generally remains low Saturday through Monday
due to discrepancies on the placement of synoptic scale features.
However, winds are expected to remain below gale force during the
period.

&&

.LONG TERM FORECAST (Days 4 through 7/Sunday through Wednesday)...

The pattern will remain amplified Sunday through Wednesday as
upper level high pressure continues to extend northwestward from
the Canadian Rockies to the Alaskan North Slope. This pattern will
allow for warmer temperatures and overall dry weather. As the
snow continues to melt and sunlight becomes more abundant and
longer in duration, the potential for convective rain showers
focused along area mountains will increase. The upper ridging will
help set the stage for convection by minimizing the potential for
widespread cloud cover and allowing ample diurnal heating at the
surface.

Upper troughing will persist across the Bering/Aleutians and
extend southeastward into the North Pacific. Due to this pattern,
the predominant storm track will be through the Bering and into
the North Pacific. A weakening low pressure system is expected to
move northwestward from the central Bering into Siberia Sunday
into Monday. A second low is expected to move eastward along the
Aleutians Monday afternoon through Wednesday. However, forecast
confidence remains low at this time due to large discrepancies in
the placement and intensity of this low.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...Flood Warning 155 (Kuskokwim River at Kwethluk)
Flood Advisory 155 (Kuskokwim River Akiachak to Napakiak).
MARINE...Gale Warning 119 120 130 131 132 136 137 138 351 352 411
413 150 155 160 175 177 178.
FIRE WEATHER...NONE.

&&

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