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000
FXAK68 PAFC 070422
AFDAFC

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
822 PM AKDT Tue Jun 6 2023

.ANALYSIS AND UPPER LEVELS...

Water vapor satellite shows broad troughing existing from the
Kamchatka Peninsula eastward though the Bering Sea into the
western Gulf of Alaska. The anchoring low pressure is centered
over the western Aleutians, however, a secondary center is moving
westward over the central Bering Sea. There are a handful of
prominent shortwaves rotating around the upper low pressure and
numerous more smaller wave embedded within the flow. The jet
stream remains south of the Aleutians, feeding energy into the
large scale trough. Looking at satellite moisture estimates show
several plumes of moisture emanating from the tropical Pacific,
bringing 100-150% of normal precipitable water for this time of
year, which is normally on the dry side.

So what does all this mean for sensible weather? Well, summer
remains in the Canadian Yukon, nosing into the central/eastern
Interior of Alaska. Near 100% cloud cover extends across the
Bering Sea into the Gulf of Alaska, and showers or periods of
rain accompanying the embedded disturbances. Breezy southeasterly
flow exists across southern Alaska, enhanced through gaps in
terrain.

&&

.MODEL DISCUSSION...

On the large scale, guidance is great agreement with the evolution
of the pattern. There will always be struggles with small scale
features and timing of embedded waves, but confidence is high in
the general pattern for the next four to five days. The general
consensus is the large upper level low will slowly drift eastward
and consolidate over the central/eastern Aleutians.

&&

.AVIATION...
PANC...VFR conditions will persist. The Turnagain Arm wind will
remain over the terminal, but should be less intense than Monday
evening, and not last through the night.

&&

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

A steady-state pattern will persist through the rest of the week
as a large upper-level low remains in place over the
central/eastern Bering Sea. A front extending northwest from the
Gulf of Alaska across the western half of Southcentral will track
slowly northward as a series of upper-level shortwaves propagate
along the front, periodically enhancing rainfall along the coastal
mountains from Kodiak Island to Prince William Sound and along
the western half of the Alaska Range. With relatively weak cross-
barrier flow and a modest moisture tap originating in the East
Pacific, each passing shortwave is also likely to trigger periods
of light rain from the western Kenai Peninsula, north through
Anchorage, and into the Mat-Su Valleys.

The slow moving front lifts inland Wednesday night, aided by a
potent shortwave pivoting around the large upper low. This will
contribute to a period of heavier rain over inland locations from
Kenai to Talkeetna, though cross-barrier flow will increase as a
result of stronger flow around the shortwave and may quickly shut
off precipitation as the feature passes through. After the frontal
passage, a lack of strong dynamics and a more limited moisture tap
will lead to lighter upslope precipitation along the coastal
mountains on Thursday and Friday. However, cooler air moving in
aloft and increased potential for breaks of sun will allow for
some inland rain showers to develop, especially over the Susitna
Valley and Copper River Basin. There will also be a slight
potential for a stray isolated thunderstorm or two in the same
regions.

Throughout the forecast period, expect diurnally driven
southeasterly gap winds, aided by a coastal ridge, with peak
winds during the late afternoon and evening hours through Friday.

&&

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

A large upper-level Bering low will promote widespread unsettled,
cloudy weather throughout the next few days. The main low center
is located over the western Aleutians with a secondary low center
moving westward over the central Bering. Multiple shortwaves
embedded within the flow will continue to rotate around the low as
it slowly tracks eastward along the Aleutian Chain. The low
center is expected to track over Adak on Wednesday and then to the
eastern Aleutians/Alaska Peninsula on Friday. As a result, expect
gusty winds and rain showers to persist, although shower
intensity and coverage gradually decrease Thursday and Friday as
the low weakens. Across Southwest, the aforementioned shortwaves
will help maintain a showery regime across the region through
Friday, with much of the rain focused along the eastern facing
slopes of the Alaska and Aleutian Ranges and Kuskokwim Mountains.

&&

.LONG TERM FORECAST (Days 3 through 7)...

Weather for the extended portion of the forecast is higher
confidence than normal due to the persistence of the upper level
low pressure currently over the Bering Sea. Guidance is in great
agreement in lingering this features over the eastern Bering Sea
through early next week which will keep much of the forecast area
cloudy, with rain along the north Gulf coast and showers
elsewhere. One feature extended guidance seems to be locking onto
is a stronger low pressure system coming from the south into the
Gulf of Alaska Saturday or Sunday which would bring a gale-force
front along with a period of steadier rain to the southwest
Mainland, Kodiak Island and the north Gulf coast. Uncertainty
increases toward the middle of next week as several features from
the Arctic and western Pacific start to influence the pattern over
Alaska. Until then, expect a continuation of cooler, cloudier,
and breezy conditions.

&&

$$

SYNOPSIS AND MODEL DISCUSSION...ML
SOUTHCENTRAL ALASKA...CQ
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...AF
LONG TERM...ML