Wildfire in Alaska, June 28 to 30, 2022

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
536 AM AKDT Tue Jun 28 2022

.ANALYSIS AND UPPER LEVELS...

A ridge of high pressure currently extends southwestward from
northern Northwest Territory to the northern Gulf of Alaska. A
vertically stacked low over the western Bering Sea will continue
to slowly move northwestward.

Closer to the surface, radar is picking up on a couple of very
light showers moving northward across the Kuskokwim Delta.

&&

.MODEL DISCUSSION...

Forecast confidence remains above average overall as guidance
remains in good agreement with the placement and intensity of
synoptic scale features. The biggest challenge will be forecasting
convection as models have a tougher time at resolving these
smaller scale features.

&&

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

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 through 3/Today
through Thursday night)...

Low level northerly flow will prevail across Southcentral today,
leading to warming and destabilization of the atmosphere. While
the flow is by no means strong, it is enough to bring a return
to hot and dry conditions for all except the immediate coastline.
Expect locally gusty offshore winds this morning, namely in
Seward/Resurrection Bay and Whittier/Passage Canal, but warming
temperatures inland should be enough to overcome the weak offshore
component and bring in sea breezes for most coastal locations.

The warming temperatures inland will lead to a thermal trough
oriented roughly E-W from the Copper River Basin to the Susitna
Valley, with afternoon/evening convection initiating along or
near this trough. As always, convective initiation will be
favored along mountain slopes. The most unstable air will be
the northeastern Copper River Basin, close to the upper level
ridge center which has been sitting over the Yukon Territory.
Secondarily, the slopes of the Talkeetna Mountains look quite
unstable as well. Storm motion will be light, with very little
wind through the vertical column. This will keep a lot of the
storms along the mountains, though a little more flow over the
Copper River Basin should advect storms out over the valley.

The upper ridge will gradually shift westward over Southcentral
through Wednesday, leading to continued warming of the low levels.
As a result, expect convection to become more widespread Wednesday
afternoon and evening. Convective initiation will be likely along
the slopes of most mountain ranges, including the Kenai and
Chugach Mountains. As would be expected, the big limiting factor
for convective initiation over the lowlands is a very dry airmass.
Some forecast soundings also show a weak inversion in the low
levels, especially near the coast where surface temperatures won't
be as hot as inland. With good confidence in initiation along the
mountains, the key to determining whether these storms will
affect any valley locations (where conditions have been extremely
dry) is storm motion. There is good model agreement on generally
weak storm motion from south to north. Honing in on any storms
which form along the Kenai Mountains and front range of the
Chugach Mountains (east of Anchorage), this means only areas very
close to the mountains will have a chance of seeing a
thunderstorm and receiving some rain. The best bet may be Eagle
River and Palmer, which are positioned sufficiently close to the
mountains. In summary, expect fairly numerous showers and
thunderstorms over interior Southcentral (Susitna Valley to the
Copper River Basin), with more isolated convection over southern
areas of Southcentral. As a result, many of the driest areas will
remain hot and dry.

A shift in pattern will begin Thursday as a high amplitude trough
over the Bering Sea progresses eastward toward Southwest Alaska.
This will start to push the ridge over Southcentral back off to
the north and east. Increasing southerly flow throughout the day
will bring marginally cooler low level air onshore of Southcentral.
As a result, the greatest instability and best chances of
showers/thunderstorms will once again be confined primarily to
interior Southcentral. Temperatures will remain quite hot inland,
but expect the increasing onshore flow will start a cooling trend
for coastal locations.

&&

.FIRE WEATHER...

Southcentral Alaska...

As mentioned in the Southcentral forecast discussion, the key
story for the next couple days will be hot and dry conditions
along with an increase in diurnal convection. By far, the most
numerous thunderstorms with frequent lightning will be focused
inland - primarily from the Talkeetna Mountains eastward across
the Copper River Basin. Expect the most widespread convection on
Wednesday, again with the vast majority of convection over
interior Southcentral. Confidence is fairly high that any storms
which form down along the Kenai and Chugach Mountains will not
stray far from the mountains. On Thursday, convection will shift
back northward with a slight cooling trend for southern areas as a
storm system approaches Southwest Alaska. While this storm will
likely bring rain to Kodiak Island, it is doubtful that any
precipitation will reach Southcentral.

Southwest Alaska...

A warming and drying trend is expected over the next few days
across Southwestern Alaska. Weak flow is generally expected today
and Wednesday with a high pressure overhead and any rainshowers
that may linger near the lower elevations of the mountain ranges
are not expected to produce lightning. Weak, upper level cyclonic
flow is developing near King Salmon and Kamishak Bay today and
embedded waves could move off this trough Wednesday when
thunderstorm potential may increase. There may also be enough
daytime heating for convective initiation and cumulus to form.
Warm 850 temperatures still may leave this environment capped,
even though the ingredients are a little more favorable than
recent days. Convective potential on Wednesday at this time
appears more favorable near the Western Alaska Range from around
Iliamna north and from roughly Sleetmute and Lime Village
eastward. A front approaches the Southwest coast Thursday. High
temperatures could reach around 80 degrees ahead of the front.
There is uncertainty at this time on how low the RHs will go ahead
of the front but it appears likely to dip to at least around 30
percent in some inland locations. Southeasterly winds will move
further inland during the day Thursday with gusty winds further
accelerated through gaps such as Kamishak Gap. Timing of this
frontal passage make a hot, dry, and windy forecast for Thursday
tricky. More moisture and a return to cooler temperatures will
follow the frontal passage.

&&

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

Other than a few hit or miss rainshowers near the lower
elevations of areas mountain ranges, high pressure over
Southwestern Alaska will bring about a warming and drying trend
over the next few days. Highs in the upper 50s near the coast to
the low to mid 70s further inland near Lime Village, Sparrevohn,
and the valleys along the Western Alaska Range.

Weak, upper level cyclonic flow within this larger ridge will be
centered approximately near Kamishak Bay and Southern Bristol Bay
Tuesday night through Wednesday. Embedded shortwaves off this
feature along with mostly clear to partly cloudy skies may allow
for surface heating and cumulus that forms may have the potential
to become an isolated thunderstorm on Wednesday afternoon. Warm
850 temperatures could keep some of the convection capped however.

Thursday through Friday night, a front approaches the
Southwestern coast that will increase winds across the entire
Southwest. Ahead of this front, temperatures could peak to around
80 degrees in the Middle Kuskokwim Valley and other localized
valleys.

&&

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

A stalled low center over the Western Bering is bringing plenty
of southerly moisture to Aleutians near Seguam Island to Nikolski
this morning. Sustained winds approach gale force and is expected
to maintain its strength over most of the Bering Sea. This front
will reach the Pribilofs and Dutch Harbor tonight and begin to
dissipate as another front over the same trajectory moves in to
replace the former front Wednesday. This secondary plume of
moisture will stream substantially more moisture further northward
well past St Matthew Island. This wave will have enough strength
and energy to sustain its progression into the eastern Bering and
reaching the Southwestern coast Thursday night. Most of the
rainfall over the next few days will be concentrated near Atka,
Nikolski, and Unalaska.

&&

MARINE (Days 3 through 5: Thursday through Saturday)...

Bering Sea/Aleutians: A low in the central Bering Sea will
push a front from the central Aleutians to the Alaska Peninsula
through Friday. There is a low probability that gale force winds
will develop over the northern Bering on Thursday along this
front, before the low tracks into the Russian Far East. Localized
southerly gale force gap winds, however, will be possible from
the eastern Aleutians through the southern Alaska Peninsula into
late Thursday. For Friday, there is a slight chance for another
round of southerly gale force gap winds through the eastern
Aleutians and Alaska Peninsula as a weak North Pacific low tracks
into the Bering. By Saturday, winds across the region remain
below gale force. Seas are not expected to exceed 20 feet.

Gulf of Alaska: With high pressure remaining in place over the
Gulf, winds less than gale force and seas less than 20 feet are
expected for the days 3 through 5 period.

&&

.Long Term Discussion (Days 4 through 7: Friday through
Monday)...

A pattern change is in store for this upcoming weekend. The ridge
of high pressure sitting nearly stationary over the Alaska-Canada
border this week will begin to be nudged eastward on Friday as a
low pressure system develops at the base of the longwave trough
set up across the Bering Sea/Aleutian Islands. As the trough
swings eastward, a weak triple-point surface low and attendant
front tracks from Southwest Alaska and the Alaska Peninsula on
Friday to the Western Alaska Range and Kenai Peninsula by Sunday
morning. Under this regime, Southwest Alaska will remain cool and
wet. For Southcentral Alaska, initially above normal temperatures
will decrease somewhat as the trough approaches, bringing a
cooler airmass and increased moisture to the region. While
rainfall will initially accompany the front as it reaches the
Kenai Peninsula, it looks to stall and dry out on Sunday. There is
some indication the weak surface low persists in the Gulf of
Alaska through Monday, providing the instability to support
rain showers along the Gulf coast and potentially over high
terrain. However, inland areas of Southcentral are expected to
remain mostly dry. Over the Bering Sea/Aleutians, a series of
shortwave troughs keep the region active with periods of rain
showers through the weekend.

&&
.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...NONE.
FIRE WEATHER...NONE.

&&

SYNOPSIS AND MODEL DISCUSSION...ED
SOUTHCENTRAL ALASKA...SB
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...VR
MARINE/LONG TERM...CQ