988
FXAK68 PAFC 151311
AFDAFC

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
511 AM AKDT Wed May 15 2024

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 through 3/Today through
Friday night)...

A high amplitude upper level ridge is building into Southcentral
from the west, leading to warming temperatures aloft and a more
stable atmosphere (as seen in the 12Z Anchorage sounding). Skies
have cleared out across much of Southcentral, with some localized
areas of mostly mid level clouds. There are some signs in satellite
imagery of patchy low clouds and fog along the Gulf coast and
into Prince William Sound. Areas of low clouds can also be found
on Kodiak Island. Under clear skies, temperatures have once again
dropped into the 20s and 30s - as the low level airmass remains
quite chilly.

The upper level ridge will build directly overhead of Southcentral
today, then very slowly shift eastward and weaken through Friday,
lingering along the ALCAN border and the Copper River Basin. At
the surface, high pressure will build northward across the Gulf to
Southcentral today. Synoptic onshore flow will combine with warm
temperatures inland to induce strong sea breezes along all coasts
today. The winds will develop early, which will provide a cooling
influence on temperatures in coastal communities.

As the ridge slides eastward, a long-wave trough over the Bering
will approach the western Gulf along with a weakening cold front.
This will bring some very light rain to southern and eastern
portions of Kodiak Island by late tonight, spreading north to
the Kenai Peninsula on Thursday. Models solutions, which had
varied significantly in previous days with track of individual
short-waves, are now in much better agreement. Guidance depicts
a negatively tilted short-wave moving into the western Gulf
Thursday afternoon, forming a weak low in the northwest Gulf
Thursday night, then tracking the trough and low eastward across
the Gulf on Friday. As a result, precipitation likely won`t make
it further north than the Kenai Peninsula, where very light rain
(and mountain snow) is likely Thursday through Friday morning.

After today`s sunshine and warm temperatures inland, increasing
clouds will lead to cooler temperatures Thursday through Friday.
The one exception will be the Copper River Basin, which will
remain warmer under the influence of the upper ridge. Instability
will be weak, but with some breaks of sun on Friday, there could
be isolated convection. Even with that, most of the region (other
than the Kenai Peninsula) will remain precipitation free for the
next few days.

-SEB

&&


.SHORT TERM FORECAST SOUTHWEST ALASKA, THE BERING SEA AND THE
ALEUTIANS (Days 1 through 3)...

The front of a Kamchatka low is beginning to impact the west
coast of Alaska, producing widespread rain and snow showers for
the region. Gusty winds both offshore and inland are expected
through tonight, with the strongest gusts of 35-45 mph occurring
near Mekoryuk and Toksook Bay over the next few hours. Strong
southwesterly flow is expected over this time, but with below
freezing air at the 850 mb level many areas at lower elevations
may see a mix of rain and snow in the morning hours and rain in
the afternoon. Winds will quickly die off tomorrow morning with
most areas along Southwest getting calm south or southwest winds.

In addition to the low impacting Southwest, a couple of shortwaves
will pass by the western and central Aleutians over the next
couple days. The first system will enter Wednesday night, giving
the western Aleutians a quick opportunity for precipitation
amounts from a trace to 0.15" and small craft force gusts through
Thursday afternoon. The next wave will enter Friday morning and
persist through at least Friday afternoon. There are still
uncertainties in the intensity and track of this wave amongst the
most recent model runs. The interaction of this wave with a future
developing upper level low in the northern Bering will play a
role in its impact on the Aleutians.

-BS

&&

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

The long term forecast for the Southern Alaska will begin with a
ridge over the Gulf of Alaska sliding east as a shortwave trough
rounds the base of a longwave upper-level trough situated over the
Bering and moves over Southwest Alaska. Model agreement regarding
the associated frontal boundary moving across the Aleutians is
mild, as a few of the models are slightly stronger than others.
However, the timing regarding this system is fairly well agreed
upon, with this system then exiting to the east late Saturday.

Sunday may offer a reprieve from any extensive cloud cover and/or
shower activity across the Southern Mainland. But, again, all
models are struggling with the track of various shortwaves
embedded within the longwave trough. While guidance shows a ridge
trying to build north from the North Pacific and western Gulf, the
GFS is advertising a quicker breakdown of the ridge, a common and
usually incorrect bias. This solution is still possible, and
would place the entirety of the Southern Mainland on the back side
of the ridge with the resultant southwesterly flow lending to a
more unsettled pattern with various waves moving along the
Aleutian Chain and across the AKPen and Kodiak Island. The result
would be more cloud cover and chances for rain across the region.
Given the consistency of the latest GFS runs and a trend of the
EC and GEM ensembles progressively leaning more toward the GFS
recently, the long term is weighted more toward the stronger
ridge solution.

For the Aleutians and Bering, the longwave trough situated over the
region will like keep conditions cool and unsettled through the long
term. Any ridging between storm systems would be brief, with the
best chance for high pressure over the Bering late Friday into
Saturday. Any warmer air associated with the ridge, though, would
likely result in widespread stratus and fog due to the warmer air
riding over the cold open waters. By the beginning of next week,
uncertainty between the models grows with regards to a low
pressure system entering the western Bering Sea, and the
subsequent progression of the system across the Aleutians, is
currently high. It is looking like the pattern of training troughs
across the Bering will continue into the next work week.

-TM/CL

&&

.AVIATION...

PANC...VFR conditions will prevail. The combination of warm
temperatures inland and increasing southerly winds up Cook Inlet
will lead to a robust southwesterly sea breeze this aft/eve.
There could even be a few gusts as the strongest push of winds
reaches Anchorage between about 00Z and 04Z.

&&


$$