Small Craft Advisory 367, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
518 AM AKDT Tue Apr 25 2023

.ANALYSIS AND UPPER LEVELS...

An upper level low stretches its frontal boundary into the
southern Gulf of Alaska that will track northward towards Prince
William Sound this afternoon. The longwave trough pattern will
then move inland to cover much of Southern Alaska. Cloud cover can
be seen on Satellite over much of the Alaska Peninsula and Kodiak
Island, moving up Cook Inlet and into the Susitna Valley.
Unsettled weather returns to the Mainland Alaska, beginning along
the coastal regions this morning. The trough weakens and
dissipates through tonight.

The next system developing in the North Pacific tracks south of
the Aleutian Chain and moves into the southern Gulf of Alaska
Wednesday/Thursday. This pattern is more complex in nature but
models are beginning to come into better agreement on it.

&&

.MODEL DISCUSSION...

Models are in good overall synoptic agreement through the short-
term. There is much better agreement with the relatively North
Pacific complex system moving towards the southern Gulf of Alaska
Wednesday/Thursday. Models are continuing to hold on to colder air
aloft, which will promote precipitation type challenges in the
forecast with this next system.

&&

.AVIATION...
PANC...VFR conditions and light winds will persist. Cloud cover
will increase throughout the day but should remain above 5000'.

&&

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

An upper level short-wave and weak occluded front near Kodiak
Island this morning will lift northward through the day, with
steady precipitation spreading northward to the eastern Kenai
Peninsula and Prince William Sound regions. Strengthening easterly
flow will enhance precipitation over western Prince William Sound
and lead to downslope drying inland from the coastal mountains.
There is little in the way of temperature advection with this
front, so but generally expect rain and snow near sea level
changing to all rain by this afternoon with diurnal heating and
warming influence of the winds coming off the water.

Precipitation will diminish tonight as the front dissipates along
the north Gulf coast. An east-west oriented upper level trough
will then lift northward across Southcentral on Wednesday, with
showers spreading inland. With warmer daytime temperatures inland,
the predominant precipitation type will be rain - with snow in the
mountains.

A digging trough over the North Pacific will lead to development
of a surface low, which will track northward into the Gulf
Wednesday afternoon then up to the north Gulf coast Wednesday
night before weakening and pushing onshore Thursday. This will
bring another round of precipitation to the Gulf coastal areas.
There will be a strong upper jet and short-wave east of the low
center, but these will shoot off toward the northeastern Gulf.
The Cordova area could see some heavier precipitation. Otherwise,
this looks like another light precipitation event. Warmer air will
accompany this system and cause snow levels to rise to 1000 feet
or higher on Thursday.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 through 3: Today
through Thursday night)...

A complex low centered over the eastern Bering Sea this morning
will continue to push an occluded front into Southwest Alaska
today, bringing snow primarily to the Bristol Bay region with some
precipitation overspreading into the Lower Kuskokwim Valley later
this morning. Bristol Bay will see the majority of the gusty east
to southeasterly winds associated with the front today, and
locations from Dillingham north are expected to receive 1 to 3
inches of snow through this afternoon. Temperatures will warm with
solar heating during the daytime hours along with a southeasterly
push of warmer air. As a result, rain may begin to mix with snow
or turn completely over to rain as temperatures approach 40
degrees this afternoon. However, the sustained period of
precipitation expected for Dillingham and interior Bristol Bay
should keep temperatures slightly lower, enough to keep
precipitation falling mostly as snow with thicker cloud cover and
the effect of evaporative cooling.

By this evening, the front weakens and precipitation turns
showery region-wide. Snow and rain showers will continue to be
supported by a quasi-stationary low centered over the eastern
Bering Sea and Southwest Alaska through at least Thursday.
Precipitation will focus primarily over the higher elevations
beyond this evening, though daytime heating will support shower
activity over the lower areas of Bristol Bay and the Lower
Kuskokwim Valley. The Kuskokwim Delta is expected to remain mostly
dry relative to the rest of Southwest Alaska. A gradual warming
trend is also expected through the week as skies trend from
overcast today to partly cloudy by Thursday, allowing the sun to
warm high temperatures into the mid 40s over the Lower Kuskokwim
Valley.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 through 3: Today
through Thursday night)...

A quasi-stationary complex low in the eastern Bering Sea will
bring continued showery conditions to the region, including the
Alaska Peninsula, through Thursday. The eastern Bering
Sea/Aleutians and AKPEN will see more widespread showers today as
the complex low swirls east of the Pribilof Islands. A
strengthening low in the North Pacific will skirt south of the
Aleutian Chain today and tonight, bringing only minimal impact to
the islands before it tracks into the western Gulf on Wednesday.
As the low in the eastern Bering weakens tonight, rain showers
will wane for the eastern Aleutians and AKPEN. A surge of colder
air rotates around the back side of the low on northerly flow
across the western and central Bering, leading to cooling
temperatures and scattered snow showers. With winds below 30 mph
across nearly the entire Bering Sea for Wednesday and Thursday,
the main hazard will be heavy freezing spray along the ice edge
west of Saint Matthew Island.

&&

.LONG TERM FORECAST (Days 4 through 7: Friday through Monday)...

A broad upper low/trough is forecast to be in place over the
Bering at the end of the work week and the start of the long term
period. Meanwhile, high pressure over western Canada is expected
to ridge northwestward and into interior Alaska through the
weekend. At the surface, a plume of moisture previously pointed at
Southeast Alaska will retrograde into Southcentral Friday into
Saturday. As a result, one of the biggest stories during the long
term period will be the potential for heavy precipitation for
coastal areas across Southcentral. There is potential for heavy
low elevation rain for locations such as Seward, and for locations
further east across Prince William Sound. This will lead to a
threat for heavy mountain snow at the higher elevations of the
Chugach and Kenai Mountains as well. Moisture will continue to
shift further and further west through next Monday as high
pressure continues to amplify over the Eastern Alaska Range and a
Bering upper low is shunted back over the Western and Central
Aleutians Sunday into Monday. The movement of the low should
promote a threat for potential gales and storm force winds over
the Western and Central Aleutians for days six and seven.
Throughout the period, temperatures will remain generally below
normal for Southwest Alaska, the Bering, and over the Aleutians.
Southerly flow over the Gulf of Alaska will keep temperatures
closer to seasonal norms for Southcentral.

&&

 $$

SYNOPSIS AND MODEL DISCUSSION...KM
SOUTHCENTRAL ALASKA...SEB
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...CQ
LONG TERM...BL