Gale Warning 309, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
440 PM AKDT Wed Apr 20 2022

.ANALYSIS AND UPPER LEVELS...
The basic weather overview today is that high pressure remains
over the mainland part of the state with a deep low in the
western Aleutians. The clouds from the front associated with this
low extends to the Alaska Peninsula this afternoon while winds are
starting to increase along the AK Pen and Eastern Aleutians.

While the upper level ridge remains in place over the Interior of
the state, the 500 mb low is now centered over the Kenai
Peninsula and extends over Southwest mainland Alaska. The colder
air aloft associated with this low is helping to destabilize the
atmosphere a little which is leading to a small low in the
northern Gulf that is seen best on visible satellite. It is also
allowing a few showers to pop-up off the Kilbuck mountains
southeast of Bethel as well. Most of Southcentral Alaska remains
under sunny skies in spite of this upper level low as there
remains a weak surface high over Southcentral and the atmosphere
remains very dry, especially at low levels. The morning sounding
at Anchorage still only has .2 inches of precipitable water in
it.

&&

.MODEL DISCUSSION...
The main global and regional models (GFS, NAM, ECMWF, Canadian)
remain in good agreement through the rest of the week with very
little difference in any synoptic-scale features. They do start to
diverge early next week, especially in the western Bering Sea.

For the near term, the small low in the northern Gulf south of
Prince William Sound is not detected by the aforementioned models,
but does show up on the meso-scale models such as the NAMnest.
Therefore this low is being tracked with the meso-scale models.

&&

.AVIATION...
PANC...VFR conditions and light winds will persist. There is a
chance that southeast Turnagain winds will develop Thursday
afternoon gusting to 15 to 20 knots.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 through
3/Tonight through Saturday)...

Quiet conditions will continue across Southcentral through tonight.
A front will enter the western Gulf by Thursday afternoon. Pre-
frontal showers will develop in the Prince William Sound area,
with more steady rain and gusty easterly winds occurring over
Kodiak through Friday. Gusty southeasterlies are also expected
along Turnagain Arm by late Thursday, however winds should not be
an issue for the Anchorage bowl. Northeasterly gap winds in their
usual locations will continue into the weekend as the associated
low tracks eastward in the Gulf. Any snow should remain confined
to higher elevations, with minor slushy accumulations possible
Friday morning in Turnagain Pass. Otherwise, although cloud cover
will increase, interior regions should remain mostly dry through
the weekend.

&&

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

An upper-level low is located over Southern Mainland Alaska and
will track northeast over the next couple days. The aforementioned
low will shear apart as it interacts with a large Bering low and a
trough that is moving east of Russia. As the upper-level low
pushes north Thursday morning, a front moving east across the
Alaska Peninsula will increase winds through the southeasterly
gaps, especially through the Kamishak Gap. Due to flow aloft being
east-southeast, this will result in some spillover precipitation
from Pilot Point south Thursday afternoon through Friday morning.
Interior Bristol Bay is likely to see some rain Friday as the
aforementioned front reaches Kamishak Gap and downsloping and
mountain blocking have less of an effect on the region. The
Kuskokwim Delta and Lower Kuskokwim Valley may some sprinkles, but
should overall remain relatively dry and overcast in the coming
days.

&&

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

An upper-level low is currently located over the Western Aleutians
and is tapping into colder air from the north to produce storm
force winds near Amchitka. Ahead of the low, in the warm sector, gale
force winds and rain will move slowly across the Chain over the
next two days. Some snow showers are possible within the cold
sector as the low tracks east, but most of this activity appears
to be south of the Chain at this time. Gusty easterly winds and
snow are expected over the Pribilof Islands Thursday morning, but
warmer temperatures should cause the snow to stick to the ground,
thus mitigating potential for blowing snow. However, visibilities
may still be reduced at times. By Friday, the aforementioned low
will be mostly out of the domain, which will make way for calm
and partly sunny conditions leading into the weekend.

&&.Marine (Days 3 through 5: Saturday through Monday)...

Gulf of Alaska: An area of low pressure south of Kodiak Island
Saturday morning moves eastward towards Southeast Alaska and
British Columbia through Monday. Its front remains draped across
the North Gulf Coast Saturday with 20 to 30 kt winds, slowly
subsiding Saturday night through Sunday as the front weakens.
Waves of 10 to 15 ft early Saturday subside to 5 to 10 ft Saturday
night into Sunday. For Monday, expect winds less than 25 kt and
seas less than 8 ft. Forecast confidence for this outlook is high.

Bering Sea: Northwesterly small craft winds are expected Saturday
for the Eastern Aleutians and AKPEN behind a departing low
pressure system moving eastward towards the Gulf. Some of the gaps
and passes especially early Saturday could be gale force. Winds
subside Saturday evening/night as the low continues moving
eastward while weakening. Seas of 8 to 10 ft early Saturday
subside to less than 8 ft Saturday into Sunday. Southerly winds
increase to 20 to 30 kt with seas building 10 to 15 ft across the
Western Aleutians/Bering Saturday in advance of a Kamchatka low.
Its front continues across the Bering Sunday through Monday slowly
weakening as it does so. Forecast confidence for this outlook is high.

&&

Long Term Discussion (Days 4 through 7: Sunday through Wednesday)...

The long term period opens up on Sunday with an upper level low
spinning just south of the Gulf of Alaska, an upper level ridge
over much of the Bering with an extension of this ridge over
interior Alaska, and a weak upper level trough to the west. Model
guidance does vary quite a bit on the evolution of the upper level
pattern beyond Monday. The GFS and GEM both show a cut-off upper
level low somewhere in the vicinity of the Seward Peninsula and
the North Slope with another cut-off upper level low south of the
Aleutian Island Chain. The EC operational remains the strongest
with this ridge in building it into much of Southcentral next
week.

At the surface, this correlates to mostly quiet and benign weather
for much of Southcentral. Some weak upper level shortwaves in the
flow may result in some shower activity on Tuesday but especially
Wednesday across mostly the mountainous terrain such as the
Talkeetnas, Chugach Mountains, Kenai Mountains, and Wrangells. A
few of these showers might make it to valley floor locations but
uncertain at this time. Overall, expect above average and mild
temperatures with 50s especially for interior areas with upper
40s/near 50 for coastal locations.

A low pressure system spinning near the Kamchatka Peninsula Sunday is
expected to send a front eastward through the Bering and
Aleutians and into Southwest Sunday night/Monday reaching the
Southwest Coast Monday evening. The EC is the most robust with the
precipitation associated with this front especially as it moves
into Southwest. Model guidance then differs on the timing and
development of another North Pacific low in the Tuesday/Wednesday
timeframe.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE... Storm Warning 178
          Gale Warning 130-132 137 138 150 155 160 165 170-177 179 180
          352 411-414
FIRE WEATHER...NONE.

&&

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