128
FXAK68 PAFC 241341
AFDAFC

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
541 AM AKDT Mon Jun 24 2024

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

Discussion:

The upper level ridge continues to remain firmly entrenched over
much of eastern Alaska today, but will become more elongated with a
gradual shift of the upper ridge axis eastwards towards the ALCAN
border. The remnants of the low Bristol Bay will retrograde back to
the south then east today as the ridge over Bering Sea begins to
breakdown in response to a shortwave trough lifts up across the
western Aleutians into the southern Bering. Models are in good
agreement with sliding the mid-level Bristol Bay low just south of
Kodiak Island with weak surface low forming along the eastern side
of the island. The 12Z PADQ raob shows a rather moist mid-level
with steep lapse rates and drier air below 850 mb. A mid-level
cloud deck is pushing through this morning but should clear out
some later today and should see sufficient instability resulting
in isolated to scattered thunderstorms later this afternoon. PWAT
values of 0.93" (12Z raob) indicate that storms will be rather
efficient rainfall producers while in their mature stage.

Thunderstorms are also expected to develop once again over the
foothills of the Wrangells and Talkeetna Mountains, as well as some
development over the Chugach and Kenai Mountains this afternoon.
Steering flow will be weak resulting in slow storm movement. PWAT
values per the PAFC raob also show a 12Z value of 0.91" and a
moist mid-level profile. While temperatures will be several
degrees cooler today given up-inlet flow, we will still be seeing
temperatures in the 70s for much of the western Kenai, Anchorage
Bowl, and Mat-Su Valley. Thunderstorm potential will then shift to
more of the Talkeetna Mountains (Mat-Su Valley) and the Copper
River Basin tomorrow and Wednesday as the system moving into the
Bering rapidly deepens and its front lifts north across the
southern AKPen and western Gulf. The front will weaken
significantly by the time it reaches Kodiak Island, but could see
some light rain over the Island by late Wednesday into Thursday.

The only other thing to mention is with a surface ridge building
over the northern Gulf Tuesday and Wednesday, should see the
Turnagain Arm, Knik, and Copper River Valley gap winds pick up as
gradient increases.

-PP

&&


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

Shower and thunderstorm chances will redevelop once more across
Southwest Alaska this afternoon and evening, although convective
instability values for Monday are slightly lower than on Sunday,
and are greatly diminished by Tuesday. The biggest change will be
the movement of the upper low to the south and east. Development
of precipitation will be driven by daytime heating and the
passage of any subtle shortwaves. The cold front of an approaching
North Pacific low reaches the coast of Southwest Alaska Tuesday,
and pushes the high pressure farther north and east into interior
Alaska.

Farther out west, models are have trended stronger with a low and
front moving across the Western Aleutians/southern Bering through
the first half of the week. Gales are expected with the leading
front, but even more from the northerly winds on the backside of
the low. Models indicate strengthening of the low after crossing
the Aleutians, which increases confidence in widespread small
craft and gales across the entire Bering late Tuesday. Some areas
between the Pribilof Islands and Central Aleutians may even see
storm force gusts. Gusty southerly winds can also be expected
along the Kuskokwim Delta coast and across Bristol Bay on Tuesday.
Mariners can expect wave heights up to 20 feet both on the Bering
and Pacific sides of the Central Aleutians, and 8 to 15 foot seas
across the eastern Bering.


&&

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

The long term begins with a ridging from western Canada north to
the high Arctic and a deep upper level low and trough over the
Bering. The ridging is likely to keep any notable systems from
reaching the Mainland, with most consolidated lows remaining over
the Bering or passing through the southern Gulf. For the Southern Mainland,
the broad southerly flow between the trough in the west and
ridging to the east will keep temperatures cooler than what has
been observed recently, but will notably increase winds through
the coastal terrain gaps. Shortwaves riding north on the southern
periphery of the ridge may keep convection active, with afternoon
and evening showers possible over the terrain. Overall, conditions
will remain similar to the past week, just slightly cooler and
windier.

&&

.AVIATION...

PANC...VFR conditions will persist through the TAF period. Winds
will remain southerly, with brief 15 to 20 kt gusts from the
Turnagain Arm possible in the afternoon hours. There will be
showers and a possible isolated thunderstorm over the Chugach
Mountains which are expected to remain east of the terminal. There
is a light chance for low level stratus to develop a marine layer
up Cook Inlet due to southwesterly winds. This currently looks
unlikely, but the southwesterly winds up the inlet will continue
over the next couple days.

&&


$$