Wildfire in Alaska, July 24 to 25, 2023

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
524 AM AKDT Mon Jul 24 2023

.ANALYSIS AND UPPER LEVELS...

A broad trough with two embedded lows exists from the Kamchatka
Peninsula east into the eastern Bering and coastal Southwest.
Over the Alaska Mainland, a closed ridge of high pressure is
centered over the Alaska-Canada (AlCan) border. This pattern
is producing very bimodal weather across the forecast domain.
Over Southcentral and interior portions of Southwest, mostly clear
skies exist (other than upper level smoke/haze from Canadian
wildfires). Middleton Island radar shows a vigorous line of storms
moving west from Canada, with hundreds of lightning strikes
detected as the complex moves over the Wrangell Mountains.

Over the Gulf of Alaska, a broad swath of fog and low stratus can
be seen on satellite. It's a little muggy out there, with plenty
of moisture in the ground from recent rains, evapotranspiration is
keeping dewpoints high. Fog and low stratus are also prevalent
over the Bering Sea and coastal Southwest Alaska, with Bethel
radar showing showers moving north along a decaying front.

&&

.MODEL DISCUSSION...

Weather models remain in decent agreement with the synoptic
features for the next few days. The main short term challenge
continues to be the degree of thunderstorm coverage over
Southcentral over the next few afternoons and evenings. The good
news is that the models are in good agreement as to the areas of
greatest potential for convective development so confidence is
increasing as to the locations and coverage amounts expected. For
Southwest Alaska, models have struggled with the inland extent of
precipitation, leading to uncertainty in rain chances and amounts
along the coast for today.

&&

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

&&

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

Overall there wont be much change in the forecast over the coming
days with weather remaining fairly steady state underneath an
elongating ridge. This morning the ridge axis is currently over
the AlCan Border with the center of the high to the east of the
Yukon Flats. Over the next 24 to 48 hours the high will elongate
and propagate west, with the ridge axis setting up from Deadhorse
south to the Kenai Peninsula. With this shift, the widespread
thunderstorm activity in the Yukon Territory yesterday, which
bled into the eastern Copper through this morning, will shift
east. Thus, scattered to widespread thunderstorm activity will be
similar today, just farther to the west and encompassing the
Copper Basin from the Tok Cutoff to Glennallen and then north and
west along the Glenn, Richardson and Denali highways. To the west
of the Chugach and Talkeetnas, high pressure should cap
thunderstorm development.

For the Cook Inlet areas and Mat-Su, expect another warm day,
though highs should be a little lower than those observed over the
weekend due a flow moving up the inlet. Areas without the maritime
influence should expect another day in the upper 70s to 80s,
particularly the Susitna Valley and Copper Basin. The Prince
William Sound region will likely have cyclical low stratus and
fog overnight and in the morning hours, before burning
off/scattering out in the afternoon and evening. On Tuesday, the
stratus is expected to move farther west and move up the inlet,
leading to morning cloud cover and possibly fog for the western
Kenai Peninsula.

&&

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

The forecast remains largely on track, with only minor changes for
the overnight package.

An occluded low pressure system in the central Bering Sea will
remain quasi-stationary as it decays through Monday night. Its
front, currently stalled out along the Southwest Alaska coast,
will decay through this afternoon, with precipitation becoming
more showery over time. With the front remaining mostly along the
Southwest coast as a result of blocking high pressure now centered
over Interior Alaska, inland portions of Southwest Alaska will
see a continuation of warm temperatures and clear skies, with
temperatures expected to climb into the mid 60s to mid 70s through
Wednesday. Smoke from distant Canadian wildfires will also begin
to move in aloft for areas under the influence of high pressure,
north and east of a line from Iliamna to Aniak. This is expected
to be low impact, primarily affecting long range visibility and
leading to hazy skies.

Fog and low stratus across the Bering Sea and Aleutian Islands
should gradually lift as a low continues to move into the Bering
Sea from Kamchatka Peninsula through today. Its front will sweep
north and east across the Bering Sea/Aleutians, reaching the
Southwest coast by Tuesday. As this new low merges with the one
previously in the Bering Sea, shortwaves moving around it will
bring a broad area of showers across the region through Wednesday.
Some uncertainty remains with the placement and rain amounts
associated with these showers, and whether a low will form at the
triple point near the Alaska Peninsula and bring heavier rain to
Southwest Alaska.

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

Models and ensemble means are in decent agreement for the long-
term in regards to synoptic features. The main feature of interest
continues to be a broad upper- level trough with a low embedded
within located in the Bering. Several upper-level shortwaves
rotating around the aforementioned low will bring unsettled
conditions to the Aleutian Chain and the Southwest coast. Gusty
southerly winds and rain are likely over the eastern Bering
Thursday into the weekend as a front associated with this low and
trough move inland. Meanwhile farther east, a ridge of high
pressure will try to maintain its hold over the northern Alaska-
Yukon border. While the aforementioned ridge attempts to build
southward over Southcentral on Thursday, models suggest that a few
weak easterly waves will develop and propagate from the Yukon
westward into the Copper River Basin. This introduces the
potential for scattered showers and possibly thunderstorms for the
end of the week and possibly through the weekend. The
aforementioned trough will gradually win and push eastward inland
towards Southcentral as we head into the weekend and beginning of
next week. Overall, expect clouds, rain, and winds to return to
much of southern Alaska in the long- term.

&&

SYNOPSIS AND MODEL DISCUSSION...CJ/KC
SOUTHCENTRAL ALASKA...CJ
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...CJ/CQ
LONG TERM...NS