660
FXAK68 PAFC 150136
AFDAFC

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
536 PM AKDT Tue May 14 2024

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

The forecast is remaining on track with showers, partly to mostly
sunny skies, and warm temperatures until Thursday. Agreement is
coming together for the front to develop a surface low near Kodiak
Island that would increase the chance for precipitation on
Thursday for Kodiak and the Kenai Peninsula. QPF will still be on
the light end. Precipitation chances spread north and east for
Friday. rux

Previous Southcentral discussion:
The cold upper level low responsible for showers (and a few
thunderstorms with hail) over Southcentral yesterday is exiting
south into the Gulf this morning. Vorticity-maxima rotating around
the north side of the low continue to produce isolated showers
early this morning, primarily from the Talkeetna Mountains south
to the Mat Valley and through Tahneta Pass into the western Copper
River Basin. Meanwhile, a surface low over the northeastern Gulf
is being pulled back westward toward the upper low center.
Middleton Island radar imagery shows a North-South oriented band
of rain tracking westward across the northern Gulf and
southeastern Prince William Sound, including Cordova. Further
west, mostly clear skies can be found from Kodiak Island north
to the Kenai Peninsula and much of the Susitna Valley.
Temperatures have once again dropped into the 30s, with isolated
areas down below freezing.

The upper level low will exit eastward across the Gulf today,
though cyclonic flow aloft, with embedded vorticity.maxima will
continue to transit Southcentral. Slightly warmer temperatures
in the upper atmosphere means conditions won`t be quite as
unstable today as they were yesterday. Still expect increasing
showers this afternoon, but fewer showers than Monday and no
thunderstorms. The favored areas for scattered showers will be
the Mat-Su near the Talkeetna Mountains (roughly Willow to
Palmer) along with the Copper River Basin - especially along
the Tok Cutoff and north side of the Wrangell Mountains.

An upstream ridge of high pressure will build eastward tonight,
then move overhead of Southcentral on Wednesday. This will cap
off convection and lead to widespread sunny skies and warm
temperatures. With a surface high building up from the Gulf,
expect stronger sea breezes along the coast. This will lead to
somewhat cooler temperatures for coastal communities compared
to inland areas.

A dissipating front from a deep low in the Bering Sea will
approach Kodiak Island and the western Gulf on Thursday. There
will be very little forcing left, but likely enough to produce
areas of very light rain. This will also lead to increasing clouds
across the western tier of Southcentral Thursday through Thursday
night. Model spread is quiet large with regard to the eastward
progression of the long-wave trough and handling of individual
short-waves. Thus, it is not clear whether any precipitation
will make it up to Southcentral.

-SEB

&&


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

A Kamchatka Low will continue to bring precipitation, gusty winds
and periods of cloudy skies to the area through tomorrow evening.
The weak ridge over the Alaska Peninsula continues to move
eastward as the cold front from this Kamchatka Low moves through
the Central/Eastern Aleutians, Southwest Alaska and the Alaska
Peninsula. Winds will continue to impact these areas and along the
Southwest coastline northward to Mekoryuk today. Through tomorrow
morning, the winds will shift to a more westerly/northwesterly
direction as the front passes. Widespread winds gusting from 30 to
40 mph and stronger winds (gusts to 55 mph) are expected around
Mekoryuk and Toksook Bay through late tomorrow morning. There will
be a sharp cutoff of strong winds with most areas from Bethel
south to New Stuyahok eastward ranging from 15 to 25 mph through
tomorrow morning. Afterward, winds will be light and calm.

Precipitation type will continue as periods of snow and rain.
Temperatures at 850mb, which is used as an indication for
advection of cold air into a region, has been trending downward
the past few model runs. This translates to a greater chance of a
rain/snow mix this evening into late tomorrow morning. A switch to
rain tomorrow afternoon is likely as temperatures warm for the
late morning and afternoon hours. However, an evening change back
to a rain/snow mix is expected. A trace accumulation of snow is
expected through tomorrow evening for most places with 1 to 3
inches for Mekoryuk and Toksook Bay this evening through tomorrow
morning. The highest QPF values are expected to be in the the
Togiak and Goodnews Bay area where 0.50" to 1.00" will fall
Wednesday through early Thursday morning. Elsewhere, QPF amounts
will be closer to 0.10" through Thursday morning. In addition to
the Kamchatka Low, a wave crosses the Central Aleutians/Alaska
Peninsula tomorrow afternoon into Thursday morning resulting in a
brief period of brief precipitation. QPF amounts from this wave
range from a trace to 0.10".

-DJ

&&

.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 and light winds, generally less than 10 kts,
will persist through the TAF period.

&&


$$