Small Craft Advisory 496, NWS Anchorage, AK

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

.ANALYSIS AND UPPER LEVELS...

High pressure remains in place across the eastern half of Alaska,
while residual cloud cover from a dissipated front remains across
most of Southwest Alaska. The full sunshine around Cook Inlet, a
large change from the previous 3 days, means most of the western
Kenai, Anchorage, and the Mat-Su is significantly warmer this
afternoon as compared with this same time on previous days. Widely
scattered thunderstorms are forecast once again in the Copper
River Basin today. A large low over the Bering is keeping the
southerly flow ongoing over much of the eastern portion of the
basin.

In the upper levels, a large upper level high remains anchored on
the Alaska/Yukon border. Weak ridging is beginning to encroach
westward into Southwest Alaska. A large upper level low and
associated trough is over much of the Bering from the Pribilofs
west.

&&

.MODEL DISCUSSION...

The models are in good agreement through Thursday afternoon.
Thunderstorm coverage remains the primary point of uncertainty,
particularly further out in time. Since thunderstorms often
produce mesoscale upper level disturbances themselves, forecasting
how those disturbances will influence the development of
additional thunderstorms. Also, how much cloud cover influences
the temperatures along the Alaska Range on Thursday is also a
point of contention, particularly regarding possible Red Flag
conditions. See more below in the Fire Weather section.

&&

.AVIATION...

PANC...VFR conditions and light winds will persist through early
Wednesday afternoon. The Turnagain Arm wind may move into the
terminal late afternoon and evening on Wednesday, resulting in
gusty southeasterly winds.

&&

.FIRE WEATHER...

Southcentral: Dry weather will continue across all of Southcentral
through Thursday. Thunderstorms will be more numerous today than
previous days from the Talkeetna Mountains east across much of the
Copper River Basin. This repeats on Wednesday, but spreads also to
the Chugach east of Anchorage and even some thunderstorms are
possible on the Kenai Peninsula, which has been relatively
lightning-free thus far. On Thursday the thunderstorms revert back
north, impacting the same areas as this afternoon. Widespread 80s
for highs are expected from the Susitna Valley east to the Copper
River Basin, with 70s expected for most of the rest of the area.
Relative humidity levels between 25 and 35 percent are expected
each afternoon in inland areas.

Southwest: There are no fire weather concerns today. On Wednesday,
isolated wet thunderstorms are possible along the Alaska Range. On
Thursday, a front will approach the coast. The wind field out
ahead of the front will move into all of Southwest Alaska,
resulting in gusty southeasterly winds. While the strongest winds
will be near the coast, along the Alaska Range, expect gusty
downsloping winds, a good amount of sunshine, and low RH values.
Thus, a Fire Weather Watch has been issued for Thursday afternoon
for the Alaska Range zone. Cloud cover will definitely be
increased on Friday afternoon as widespread wetting rains move
into Bristol Bay and the Kuskokwim Delta. However, if it can
remain relatively sunny then the stronger winds could result in
even more extreme fire weather conditions in the Alaska Range
again on Friday afternoon. Stay tuned.

&&

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

Overall, little has changed since the previous forecast package. From
tonight until Thursday, the primary concern continues to be
thunderstorm activity along the mountains of the Southcentral
Mainland. With the upper-level ridge remaining largely stationary
overhead, we will see a continuation of clear skies and warmer
temperatures. Thunderstorms will form under the thermal trough
and, with weaker flow aloft, should remain fairly close to the
mountains. Although an occasional storm may drift off the
mountains, most of the lower elevations should remain fairly dry.
Thunderstorms today will remain mostly along the Wrangell
Mountains and Talkeetnas. On Wednesday, the extending thermal
trough will help initiate thunderstorms along these same areas, as
well as the Chugach Front Range and Kenai Mountains.

Thursday marks a transition back towards a cooler and wetter
regime as a low in the Bering Sea pushes its front towards
Southcentral. Cooler, southerly flow ahead of this front will
bring a slight drop in temperatures along the coast and from the
Kenai Peninsula north towards Susitna Valley. This will lead to
more stable conditions and limit convection to the Talkeetna
Mountains and Copper River Basin, where warmer and drier
conditions will keep their hold. By Friday morning, Kodiak Island
will see light to moderate rainfall as the front moves overhead.
Cloud cover will increase across Southcentral through Friday, and
convective potential will diminish greatly.

&&

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

High Pressure over much the region is continuing to bring a
warming and drying trend to the domain for the next couple days.
Temperatures will dip to the upper 40s to low 50s tonight before
rising to the upper 60s to low 70s Wednesday, with some areas
reaching as high as 80 degrees Fahrenheit near the Middle
Kuskokwim Valley. Weak, upper-level, cyclonic flow centered near
Kamishak Bay and Southern Bristol Bay tonight through Wednesday could
supply enough support to have wet isolated thunderstorms
Wednesday afternoon. Embedded shortwaves from this feature, along
with mostly clear to partly cloudy skies, could allow for surface
heating and cumulus to spark off the possibility of wet isolated
thunderstorms mainly near the Alaska Range. A front associated
with a low located in the Bering Sea will approach the coast
Thursday. This will result in gusty southeasterly winds,
especially along the coast. Expect gusty downsloping winds along
the Alaska Range, higher temperatures, and low relative humidity
values. As a result, a Red Flag Warning has been issued for
Thursday afternoon until 1AM AKDT Friday for the Alaska Range and
eastern portion of the Middle Kuskokwim Valley zones. Cloud cover
will increase for Friday afternoon as widespread rain showers will
move into Bristol Bay and the Kuskokwim Delta as the
aforementioned front pushes through the region.

&&

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

An upper-level low is currently stalled over the western Bering
with its associated front bringing small craft southerly winds and
moisture into the central Aleutians. This front will reach the
Pribilofs and Dutch Harbor later tonight before dissipating as
another front with a similar track moves in to replace the former
front for Wednesday. The aforementioned front will have a greater
moisture plume associated with it than its precedent, and will
push moisture all the way north past Saint 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. Expect high end southerly small craft winds
along and ahead of the front with small areas of gales near bays
and passes as the front tracks eastward towards Southwest. Most of
the rainfall over the next few days will be concentrated near
Atka, Nikolski, and Unalaska.

&&

.MARINE (Days 3 through 5: Friday through Sunday)...

Bering Sea/Aleutians: A complex of lows in the northwestern
Bering Sea and a triple-point low south of the Aleutian Chain on
Friday will push a front along the Southwest Coast and across the
Alaska Peninsula inland over Southwest Alaska and into the western
Gulf of Alaska through Friday night. There is a possibility that
gale force winds will develop over the eastern Bering along this
front before the front moves inland and weakens Friday night.
Localized southerly gale force gap winds, however, will be
possible on the north side of the Alaska Peninsula through Friday
night. By Saturday, winds across the region diminish below gale
force. Seas are not expected to exceed 20 feet.

Gulf of Alaska: There is some potential that a front entering the
Gulf of Alaska late Friday will result in gale force winds
through the Barren Islands and Kamishak Bay into Saturday. By
Saturday night, the front weakens and winds fall below gale force.
Seas less than 20 feet are expected for the days 3 through 5
period.

&&

.Long Term Discussion (Days 4 through 7: Saturday through
Tuesday)...

Models remain consistent with a longwave trough over the Bering
bringing a triple point low from the Alaska Peninsula into the
Gulf of Alaska by early Saturday morning. Height falls associated
with the longwave trough, and also the low over the Gulf, will
help to promote cooler temperatures across Southwest and Kodiak
Island along with increasing precipitation chances. An active
pattern over the Aleutians and the Bering Sea will persist into
early next week with multiple disturbances forecast to lift across
the region within the longwave trough's overall cyclonic flow.
While precipitation chances will also begin to increase into
portions of Southcentral, the best chance for showers will likely
be confined to coastal regions, as southerly flow brings Gulf
moisture over the higher inland elevations. Across Southcentral, a
persistent ridge of high pressure is forecast to get nudged
slightly eastward. While the region should be situated on the
cooler side of the ridge, overall temperatures across Southcentral
are expected to remain at or above normal into early next week.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...NONE.
FIRE WEATHER...Red Flag Warning: 153 163.

&&

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