FXAK68 PAFC 280100
Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
500 PM AKDT Mon Jun 27 2022
.ANALYSIS AND UPPER LEVELS...
Very little has changed objectively from the past few days
regarding the current analysis. In Southcentral, eastern areas
remain cloud free to start the day but are developing convection
this afternoon. The marine stratus layer moved into the Cook Inlet
region for the third consecutive day this morning, but has long
since dissipated from most areas. Much more broken marine stratus
continues across all of the Gulf as compared with previous days,
as the high pressure area shifts over to the eastern Gulf.
Across Southwest Alaska, most of the area is under a broken
stratus deck, as lingering moisture associated with an essentially
dissipated front keeps the cloud cover in place. Further,
southerly flow continues to move Pacific moisture into the area in
the form of cloud cover. Unfortunately, no much needed rainfall is
expected except on the stray shower or two that forms this
afternoon due to solar heating.
A large low is over the western Bering. This is drawing a plume
of Pacific moisture northward into the central Bering. Very little
in the way of impacts are occurring as a result of this low. Broad
southerly flow from the coast of the mainland through the Central
Aleutians is keeping a steady southerly breeze going through the
In the upper levels, a large upper level high remains centered
along the Alaska/Yukon border with a large upper level low
centered over the western Bering. A 70 kt southerly jet streak is
along the Alaska Range into northern Alaska.
The models are in good agreement through Wednesday afternoon. The
main points of uncertainty really fall to mesoscale differences in
the coverage and locations of thunderstorm development across
Southcentral through Wednesday. This is partially tied to how far
south a fast-moving front moves across northern Alaska. The models
have been coming into better agreement on this feature, however,
with most suggesting there will be very little if any influence by
this feature on the weather anywhere in southern Alaska. Forecast
confidence is high.
PANC...VFR conditions and light winds will persist.
Southcentral: Fire weather conditions will be gradually
deteriorating. An upper level high that for the most part remains
in place the next couple days will keep the Copper River Basin in
particular on the hot and dry side. That said, the heat will
increase the instability over that area. Thus, isolated
thunderstorms are expected this afternoon as a few storms are able
to break the cap. On Tuesday the high weakens and moves further
east into the Yukon. This will allow an easterly flow to collide
against the Alaska Range and Wrangell Mountains. Combined with
available moisture and instability, widely scattered wet storms
are expected, which may cause additional fire starts. Instability
thunderstorms are likely further west along the Alaska Range and
in the Talkeetnas on Tuesday. By Wednesday, convective coverage
will increase by leaps and bounds aerially. Widely scattered wet
thunderstorms are expected from the Kenai Mountains through most
of Anchorage, the Mat-Su, and over to the Copper River Basin.
While there will be very little in the way of forcing, full
sunshine combined with a continually weakening cap will allow for
widely scattered pop up thunderstorms. With zero in the way of
flow, the storms will largely rain themselves out and any forcing
for new storms will be the gust fronts of old storms.
Southwest: A dissipating front, widespread cloud cover, and much
cooler temperatures will keep all fire weather concerns minimal
this afternoon and Tuesday. On Wednesday, upper level ridging
moves over Southwest Alaska, which should allow enough instability
to develop for a few isolated thunderstorms to form in the Alaska
Range and in parts of the Kuskokwim Mountains.
.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 through 3:
Tonight through Thursday)...
A longwave ridge persists over Eastern Alaska. The marine layer
that has been creeping up Cook Inlet for the past several days is
expected to remain at bay through the short-term. With clearing
skies ahead, expect temperatures to climb into the 70s and 80s.
These higher temperatures will lead to an increase in thunderstorm
activity for the next several days. Today`s thunderstorms should
remain mostly limited to the northeastern Copper River Basin.
However, the areal coverage of thunderstorms is expected to
increase through Tuesday and Wednesday afternoon.
For Tuesday, thunderstorms are expected across the northern
Copper River Basin and Talkeetna Mountains. On Wednesday and
Thursday, thunderstorms will spread across much of the Copper
River Basin and extend from the Talkeetna Mountains, through the
Chugach Front Range, and to the Kenai Mountains. There remains
some question about how intense these thunderstorms, and their
lightning activity, may get. While there will be a considerable
amount of instability associated with the thermal low, weak winds
under the ridge and little in the way of forcing suggest that
these storms will not become well-organized or particularly long-
lived. Weak steering flow will likely keep these storms, and their
rain, restricted to the mountains.
.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 through 3:
Tonight through Thursday afternoon)...
The front that brought rain and widespread cloud cover to much of
Southwest will continue to dissipate heading into the overnight
hours. Any residual rain showers are expected to dissipate near to
just after midnight. Upper level heights will continue to build
over much of Southwest as a weak upper level ridge moves overhead.
As a result, the next few days will feature drier, warmer, and
sunnier conditions especially for interior Bristol Bay and the
Middle Kuskokwim Valley. However, there will be some embedded weak
upper level shortwaves traversing around this weak ridge. Due to
this, there is the risk for afternoon and evening convection.
Tuesday continues to look very marginal as weak shortwaves move
over the region and instability remains weak. Think anything that
develops will mostly be rain showers. Also, 850 mb temperatures
are warming indicating a capping inversion aloft.
Wednesday and Thursday, instability continues to increase as the
weak ridge remains overhead. However, the upper level shortwaves
will be a bit stronger on Wednesday before becoming even stronger
on Thursday providing more lift in the atmosphere each day. In
conjunction with the shortwaves becoming stronger, 850 mb
temperatures continue to warm indicating a strengthening capping
inversion. Therefore, the convection forecast remains rather
difficult for these 3 days as anything that tries to develop will
have to punch through the cap. It may very well just end up being
towering cumulus clouds that develop that never mature into a
thunderstorm. Also, the most likely places for convection if it
did come to fruition would be across the Western Alaska Range
mainly from Lime Village east and the Ahklun Mountains/Kilbuck
Mountains. Temperatures also become warmer each day with Wednesday
and Thursday being the warmest days with widespread 70s and
perhaps even an 80 degree reading in the Middle Kuskokwim Valley.
Closer to the coast temperatures will remain in the 50s to 60s.
.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 through 3:
Tonight through Thursday afternoon)...
Upper level troughing remains across the Bering for the next
couple days keeping the area unsettled. A low pressure system
currently located northwest of Adak moves northward and then
northwestward into the southwest Bering Sea Tuesday and virtually
stalls. Its associated front continues moving eastward along the
Aleutian Chain reaching Dutch Harbor and the Pribilofs Tuesday
afternoon. The front is expected to stall here overnight as
it bangs against the strong ridge to the east halting its eastward
progress. As a result, it will undergo frontolysis (decaying
front) Tuesday night. Another system moves towards the Central
Aleutians Wednesday morning bringing another round of unsettled
weather. This system continues northward into the Bering Wednesday
night spreading periods of rain and gusty winds eastward towards
the Eastern Aleutians and southern Alaska Peninsula for Wednesday
night through Thursday. The Pribilofs will also get in on the
action Wednesday evening through Thursday as the low pressure
system moves northward through the Bering and sends its front
eastward through the area. This system also looks to be much
wetter than the previous one as it brings a deeper fetch of
moisture northward from the North Pacific.
.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
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.
SYNOPSIS AND MODEL DISCUSSION...JW
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...MV