Gale Warning 403, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
458 AM AKDT Fri Jun 23 2023

.ANALYSIS AND UPPER LEVELS...

The overarching pattern continues to change very little, with the
Pacific jet still mostly removed from the picture well to the
south of Mainland Alaska and the Aleutians. Lack of stronger mid
to upper flow is keeping the pattern extremely stagnant, with the
change in position and strength of most larger scale features
nearly identical to where they were 24 hours ago. Across the west,
a very broad region of cyclonic flow remains established around a
stacked Bering low. This is focusing bands of rain and low
stratus along the low's occluded front wrapped multiple times
around the parent center. The wind field around most of the low
remains quite weak, with all but the central Aleutians seeing
winds below small craft range. A corridor of southeast flow along
the low's front is also reaching the southern AKPen, leading to
gusty southerly winds out of favored gaps and passes. Most of
Southwest remains fairly quiet aside from widely scattered showers
and areas of low cloud cover.

Shifting attention back east, a weak low that has meandered south
of Kodiak for days is finally beginning to lift north as an open
wave, negatively tilted trough. To the north, a longwave ridge
still extends from Northwest Canada into much of the Mainland.
This is keeping steady, weak southeast flow focused over
Southcentral, which has helped support a bit of drying over
interior valleys where favored by downslope flow off of the
Chugach and Kenai Ranges, but low level moisture remains higher
than average. Areas of rain showers have become more concentrated
along the coast between the Kenai Peninsula and Prince William
Sound, as well as along parts of the Alaska Range, where there is
added support from upslope flow.

&&

.MODEL DISCUSSION...

Models are in good agreement with most larger scale features
through the weekend, but some differences are persisting for the
fate of the shortwave trough currently over the gulf and the
stronger system moving up from the North Pacific shortly
afterwards. Solutions are in agreement that the first trough over
the Gulf will continue to lift north into Southcentral on
Saturday, but vary somewhat with the speed of northward
progression. The GFS has generally been the slowest solution,
depicting the trough axis lifting up into the Copper Basin several
hours later than the current consensus. This has some implications
for potential for convection over namely the Susitna Valley and
Copper Basin. A later arrival of the trough in the afternoon on
Saturday would favor better chances for daytime heating and higher
instability before cooler temperatures and dense cloud cover
arrive with the trough, and overall higher chances for
thunderstorms across northern parts of Southcentral.

Looking to the next system entering the gulf on Sunday, there are
similar timing, track and strength differences appearing in recent
solutions. The NAM is the most noteworthy outlier, with the most
recent runs pushing the trough and it's associated surface low
farther east over the Gulf and much faster north than any other
model is showing on Sunday. Other differences in the timing,
orientation and track of the low and supporting shortwave are
leading to uncertainty in the strength and location of stronger
winds around the low, as well as out ahead of the system over the
Kenai Peninsula and Chugach Front Range.

&&

.AVIATION...
PANC...VFR conditions will persist. Similar to yesterday, winds
blowing out of the Turnagain Arm are expected to bend into the
terminal later this afternoon and evening. Winds will also be
similar in terms of intensity compared to Thursday, with gust up
to 25 kts possible this afternoon.

&&

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

Low clouds and patchy fog have been primarily confined to
Kachemak Bay area, Kodiak, Seward, and the northern Gulf near
Cordova/Middleton Island this morning. As cloud cover moved into
Cordova, the visibility improved. A burst of rain showers moved
across Kenai to Anchorage and Palmer with little reduction to
ceilings.

With predominantly southeasterly flow continuing for
Southcentral, showers remain possible with the highest likelihood
being near terrain with orographic lift. Further inland where
clearing skies and surface heating is possible, convective mixing
and afternoon instability could increase chances for rain showers
and isolated thunderstorms. The low influencing this unsettled
weather pattern in the Gulf has started to move north and expected
to move inland this weekend.

A gale force front associated with a Bering low, will follow on
the heels of the passing Gulf low beginning Saturday evening in
the western Gulf/Kodiak. Expect widespread precipitation with this
stronger system. Peak timing for the winds appears to be early
Sunday. As the front quickly lifts north, gales will become more
easterly and hug along the entire northern Gulf coast. This has
the potential to funnel strong winds through Prince William Sound,
Passage Canal, and Turnagain Arm. The challenge with this system
will focus on the potential for 50 kt winds or greater and if
there will be any further enhancement due to terrain. Expect
details in the forecast to change as this system evolves.

&&

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

Broad low pressure remains in place in the southern Bering Sea
just north of Atka over the next couple of days. Low marine
stratus cloud cover encompasses essentially all of the Bering
Sea, spilling into Southwest Alaska due to persistent
southeasterly flow. As such, a cloudy, wet, showery patter
continues across Southwest Alaska and south along the Alaska
Peninsula and Eastern Aleutians. There may be periods of breaks in
the cloud cover along the Western Alaska Range at times, which
could promote thunderstorm development Saturday and Sunday
afternoon. However, if there is no cloud cover, the chance for
thunderstorms drops drastically. Either way, anticipate rainfall.
A North Pacific low develops at the base of the associated trough
and tracks northwards towards Kodiak Island Saturday afternoon.
The low itself is not particularly strong, but will allow for
increased winds through Kamishak Gap into Bristol Bay through
Saturday night into Sunday morning.

&&

.LONG TERM FORECAST (Sunday through Wednesday)...
By Sunday the entire forecast area will be under the influence of
the stacked Bering Sea low pressure. In additions, a disturbance
rounding the trough will amplify as it interacts with a frontal
boundary in the northern Pacific Ocean. The deepening system will
approach just east of Kodiak Island, though there is some
uncertainty with exact strength and position. There is higher
confidence that it will bring rain to much of Southern Alaska,
though the Mat-Su/Anchorage Bowl/western Kenai Peninsula will see
some downslope drying. Enhanced winds are also higher confidence
along the Anchorage Hillside, Turnagain Arm, and along the north
Gulf coast through Barren Islands and Kamishak Gap into Interior
Bristol Bay. We remain under the influence of the large Bering Sea
trough beyond the weekend into the mid-week timeframe with likely
more disturbances tracking into the Gulf of Alaska bringing active
weather and generally cloudy and rainy conditions.

&&

SYNOPSIS AND MODEL DISCUSSION...AS
SOUTHCENTRAL ALASKA...VR
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...KM
LONG TERM...KZ