Gale Warning 385, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
401 PM AKDT Sun Apr 14 2024

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

The near-term forecast of sunny and benign weather remains on
track through Monday evening. From Tuesday afternoon through
Wednesday, however, major forecast updates have been made for the
next storm moving in near Kodiak Island. For this storm, we're
monitoring the potential for heavy precipitation/flood potential
and strong winds for Kodiak Island.

Diving into the details...a high pressure ridge is currently
moving in from the west, creating a beautifully sunny Sunday for
all of Southcentral Alaska. Temperatures climb into the 40s this
afternoon under abundant sunshine, leading to localized areas of
sea breezes along the coast. Gusty gap winds through Whittier and
Seward will linger through early Monday morning before shutting
off as the ridge firmly establishes itself overhead.

Similarly pleasant weather is expected through most of Monday,
but cloud cover and precipitation chances increase by evening as
a shortwave over Western Alaska begins to displace our fair
weather ridge. As the ridge moves eastward, southerly flow behind
it will lead to light upslope precipitation along the Gulf coast
of Kodiak Island, the Alaska Range, Eastern Kenai Peninsula, and
Prince William Sound.

From Tuesday through Wednesday, two lows merge south of the Alaska
Peninsula and push a front northeastward into Southcentral. The
biggest change since the previous forecast package has been to
speed up the front's progression and greatly increase precipitation
amounts for Kodiak Island. We have moderate confidence that the
Gulf coast of Kodiak Island will see sustained winds to gale force
and moderate to heavy precipitation from Tuesday night through
early Wednesday morning.

What's less certain is the total duration of precipitation for
Kodiak Island. There is a chance that Kodiak Island could see
sustained moderate to heavy precipitation through Friday, which
could lead to flooding concerns. Ultimately, this will depend on
the evolution of the low complex south of the Alaska Peninsula,
and how embedded surface lows affect the orientation and track of
the front. Given how impactful this front could be, please stay
tuned as we continue to update the forecast.

-KC

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA, BERING SEA, AND ALEUTIAN
ISLANDS (Days 1 through 3: Tonight through Wednesday)...

This afternoon, the eastern Bering Sea and Southwest mainland
Alaska are under high pressure at the surface and aloft, while a
fairly strong low is entering the southern Bering Sea near Adak.
The high pressure has kept precipitation out of the area, but
large portions of southwest Alaska are under stratus clouds as a
result of the subsidence underneath the ridge. These clouds are
unlikely to break except for some areas in the Bristol Bay region
through early this evening. After that, they should pack in again.

The low near Adak is not going to waste much time moving to the
north as it is expected to be just west of Nunivak Island Monday
afternoon and then up to the Bering Strait Monday night. The
majority of impactful weather in the region will be associated
with this low, and especially along the front as it moves over
the Pribilof Islands late tonight and to the Kuskokwim Delta
coast Monday. This front will bring strong winds across the Bering
Sea region. One of the biggest forecast questions will be how
much blowing snow develops for the Pribilof Islands tonight and
the Kuskokwim Delta coast tomorrow. The winds in these area will
be south-to-southeast which puts them in the warm advection sector
of the low. In spite of this, the amount of cold air aloft should
be sufficient to keep precipitation type mostly snow or all snow
for these areas. The timing of the front tonight in the Pribilof
Islands makes it more likely to get some blowing snow there, but
there is also all open water near them which should keep temperatures
just at freezing or a little above freezing all night. While
precipitation will remain snow, it will likely limit the amount of
blowing snow to the heaviest precipitation just before frontal
passage and the limited visibilities may be more due to snow
intensity and winds and not from resuspended snow since the snow
will be wet and heavy. This heavy, wet snow will also visit
Nunivak Island and then western coast line of the Kuskokwim Delta
tomorrow afternoon. Precipitation should remain snow there as
well, but blowing snow will be limited to the most intense time of
snowfall due to temperatures being at or above freezing for most
of the event.

After this low moves through, southwest Alaska and the eastern
half of the Bering Sea will remain in an active weather pattern as
a cold upper level trough digs southward into the central Bering
Sea Tuesday night into Wednesday. At the same time, a low south of
the Gulf of Alaska will track toward the Alaska Peninsula bringing
in warm air and a lot of moisture.

&&

.LONG TERM FORECAST (Days 4 through 7: Thursday through Sunday)...

An amplified pattern will be in place on Thursday with a longwave
trough stretching from western Alaska to south of the Eastern
Aleutians. Anchored in place, through at least Thursday, will be
a vertically stacked low to the south of the Alaska Peninsula.
Enhanced northerly flow over the Bering with below normal
temperatures are forecast across the Bering into the Central
Aleutians Thursday. Downstream of the trough, southeasterly flow
will bring plentiful moisture into the western Gulf along with
warmer temperatures. Kodiak Island, in particular, will be in the
cross hairs of a potential atmospheric river. With an initial
round of precipitation on Wednesday, renewed and heavier rainfall
will be possible Thursday into Friday as the stacked low south of
the AKPEN remains largely stationary. There is quite a bit of
uncertainty in how far north the front and steady precipitation
will make it. Portions of the Kenai Peninsula and Prince William
Sound could see a period of steady precipitation (primarily in the
form of rain at sea level) mid to late week, or it could stay
mostly dry if the front stalls to the south. Details to resolve
over the coming days will be how far south and west the low moves
while south of the AKPEN. The deterministic GFS continues to trend
well west of ensemble guidance, which could change the location
of the atmospheric river entirely by the middle of next week, and
will certainly have implications on precipitation chances for
Kodiak as well as the Gulf coast.

BL

.AVIATION...

PANC...VFR conditions and light winds will persist through Monday
morning. The Turnagain Arm wind will return late Monday afternoon
and evening in response to the Bering low tracking up the west
coast of Alaska. With the low so far away, the winds will be gusty
but this will be a "weaker" wind event as far as these tend to go.

MTL

&&