Gale Warning 385, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
505 AM AKDT Thu May 18 2023

.ANALYSIS AND UPPER LEVELS...

A high amplitude pattern remain in place over much of the State,
including both the Bering Sea and the Gulf of Alaska. Out west,
high pressure sits over the Western Aleutians and western Bering
Sea, with weakening low pressure over the Yukon Delta and its
associated trough stretched across the eastern Bering Sea. On the
eastern side, high pressure ridging extends from western Canada
to the Gulf of Alaska. Snow has been a product of the continued
cold air pulled out of the north over the Kuskokwim Delta. Most
of the precipitation over Bethel has subsided but observations
over Mekoryuk and portions of the immediate Kuskokwim Delta coast
continue to show periods of snow overnight.

The next main weather driver will follow a front extending off a
North Pacific low pushing towards the Alaska Peninsula/Kodiak
Island. The front reaches the southern Gulf of Alaska late tonight
and will push over the AKPen through Friday afternoon.

&&

.MODEL DISCUSSION...

Models remain in good overall synoptic agreement through the short
term. They continue to have a good handle on an approaching North
Pacific low and its associated front that will look to be the next
weather driver for Southcentral Alaska.

&&

.AVIATION...

PANC...VFR conditions and light winds will persist.

&&

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

An upper-level ridge over Southcentral will allow generally clear
and very dry conditions to persist through Friday morning.
Northerly gap winds along the coast will continue in earnest
through the morning hours before diminishing this afternoon as
diurnal sea breezes try to develop with temperatures climbing into
the 60s along the coast. Farther inland, widespread 60s are
expected with some areas in the Copper River Basin and Mat-Su
Valleys potentially reaching 70 degrees. North-northeasterly winds
will also develop later this afternoon and continue through the
evening and overnight hours for these locations due to an
increasing pressure gradient between the ridge over the interior
and a low south of Kodiak Island.

For Friday, a surface front will move from the Gulf of Alaska
north to the Southcentral coast. Rain will over spread the
immediate coast and coastal mountains, lingering through Saturday
as the front stalls and weakens. Isolated showers will be possible
for interior locations, especially across the northern half of the
Susitna Valley and Copper River Basin.

The bigger story will be the return strong southeasterly gap winds
late Friday morning through Saturday morning, with the peak
expected Friday afternoon and evening. Expect wind gusts to 35
mph across parts of the Anchorage Bowl, Knik River Valley, and
Copper River Basin. Wind gusts to 45 mph are possible through
Turnagain Arm.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA/BERING SEA/ALEUTIANS (Days
1 through 3: Today through Saturday night)...

An upper-level low and inverted trough over the Yukon-Kuskokwim
Delta and stretching across the eastern Bering Sea, respectively,
will retrograde westward today in response to a ridge building across
southern mainland Alaska. The ridge will extend westward as a low
centered several hundred miles south of Kodiak Island advects
warmer air from western Canada into the region. As the low
tracks northwest, it will induce offshore flow and northerly
winds will increase today across Southwest Alaska and the eastern
Bering Sea, allowing low stratus to clear out today. The
combination of the the warmer air mass and clearing skies will
allow temperatures to reach into the mid to upper 50s today across
much of interior Southwest Alaska, with more moderate temperatures
along the coast. By this afternoon, the low in the North Pacific
pushes its occluded front to the Alaska Peninsula, where
precipitation will fall mostly as light rain. Some snow may mix in
initially for locations from Cold Bay and King Cove west, where
antecedent conditions are cool enough, but will change quickly to
rain as the front progresses westward.

Friday is expected to be even warmer than today for Southwest
Alaska, with interior locations approaching 70 near Sleetmute and
Stony River. Further south, the low tracks closer to the Alaska
Peninsula, bringing gale force winds to the coastal waters on the
south side by Friday night. A chance for light rain showers tracks
northward into Southwest Alaska Friday evening as well with colder
air wrapping in around the low. By Saturday, temperatures moderate
somewhat, but will remain near normal, with the warmest air
retreating into interior Alaska. The south side of the Alaska
Peninsula continues to see light rain, while the low's occluded
front weakens and dries out over the central Aleutians. By
Saturday night, much of the region sees relatively benign
conditions as the slow-moving low decays over the Alaska
Peninsula.

&&

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

The long term forecast is coming into better focus this afternoon
with both deterministic and ensemble guidance in fairly good
agreement through early next week. The 12z ECMWF deterministic and
ensemble runs were late coming in this morning, so will press on
without the help of the western peninsula of Eurasia. A broad
upper trough should be in place over the Eastern Aleutians and
Alaska Peninsula at the start of long term period on Sunday. This
trough of low pressure is expected to linger over the same general
area through early next week. Which should lead to more unsettled
conditions from the Eastern Aleutians up into the Alaska
Peninsula. Increased cloudiness and scattered showers will be
common. Additionally, southerly flow from the Pacific side will
bring increased moisture into the eastern faces of the eastern
Aleutian Mountains, as well as into Kodiak Island. Thus, cooler
and below normal temperatures, as well as above normal
precipitation chances, are forecast from the Eastern Aleutians
into Kodiak Island.

Over the western Bering, Southcentral Alaska, and much of
Southwest Alaska, high pressure is expected to persist. A warm-up
trend over Southwest Alaska the next few days will continue into
the weekend and early next week. As a result, warmer conditions
and clearer skies are forecast from Southwest Alaska into
Southcentral Alaska for the long term period.

Some uncertainty does arise by Wednesday as models suggest the
trough over the Alaska Peninsula will begin to pivot northward.
Increasing clouds and a chance for scattered showers may gradually
expand from the AKPEN up into interior Southwest and the Kenai
Peninsula by the middle of next week.

&&

SYNOPSIS AND MODEL DISCUSSION...KM
SOUTHCENTRAL ALASKA...TM
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...CQ
LONG TERM...BL