Gale Warning 859, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
534 AM AKST Fri Nov 29 2024

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

A slight shortwave ridge will move overhead today, relaxing some
of the gradient and winds through the mountain passes and gaps.
Temperatures have cooled once again under completely clear skies
tonight with many wind free areas ranging from 0 degrees down into
the negative twenties. Areas with winds remaining are in the teens
to low twenties. Looking ahead, a closed arctic upper low will
move south towards the Alaska Range before taking a westward
departure into Southwest and the Bering Sea on Sunday. This will
induce some cloud cover and reinvigorate winds through the
mountain gaps and passes. Some very light snow is possible near
the Alaska Range and Talkeetnas, but otherwise the airmass should
remain too dry for precipitation. Another feature of note is a
weak inverted trough that will swing west into the Kenai Peninsula
and Kodiak Island. Precipitation will be very minimal for these
areas. Some guidance is indicating some light snow for the western
Kenai as well, but dry air will need to be overcome.

By late Sunday a significant pattern change will take hold, one
that model guidance is indicating will last 1-2 weeks. The deep
upper low over the Bering will drop south into the north Pacific,
building heights and ridging over the Gulf and really the whole
west coast of North America from California north. This pattern
looks to remain highly amplified as the deep upper low lingers in
the north Pacific. Many low pressure systems are expected to
develop over the next week and move into southern Alaska and the
Gulf. For late Sunday and Monday, a week shortwave an inverted
trough will move into the coast bringing very light precipitation
to the immediate coast. As we move into next week, expect
temperatures to climb to near or above freezing for many areas,
with increasing chances for rain and freezing rain. Each
individual system is very poorly resolved, but the signal of above
normal precipitation and temperature is unambiguous.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA/BERING SEA/ALEUTIANS (Days
1 through 3/Today through Monday)...

Southwest Alaska continues to experience clear and cold conditions
due to a large high that is centered over the northern Bering
Sea. A large North Pacific low south of the Aleutian Islands has
sent a front northward, impacting the Southern Alaska Peninsula
and the Eastern Aleutians in the form of rain showers and gusty
winds especially through bays and passes. This is also keeping
temperatures warmer than the mainland, with temperatures in the
40s across the Aleutians. The interaction between the high and the
front has allowed easterly offshore winds in the coastal regions
of southwest Alaska to prevail. This is advecting cold air off of
the mainland which is contributing to the advance of sea ice from
the Kuskokwim Delta and Bristol Bay coasts. Freezing spray is
another consequence of this offshore easterly flow.

Saturday will bring significant changes as an Arctic low barrels
across the state and quickly pushes into Southwest Alaska. This
low will kick the high out of the region towards Russia and will
finally allow the remnants of the North Pacific low to advance
northwards. Very cold air will accompany this low, increasing the
easterly offshore flow from before. Sea ice will further advance
and the aforementioned freezing spray will become heavy as gale
force winds flow offshore from the Kuskokwim Delta and Bristol Bay
and will last through Monday. The severity of the freezing spray
will be mitigated by the still relatively warm sea surface
temperatures and the advance of the sea ice itself (lower wave
heights). Wind chill will be another concern Saturday night
through Sunday night with temperatures feeling like -20F to -30F
with the colder values being felt further north. The cold air
will also allow for instability as it moves over the relatively
warmer ocean waters, and combined with lift from the low,
widespread snow showers will form in the Bering Sea. The
Pribilofs, Eastern Aleutians, and Southern Alaska Peninsula will
be impacted by these snow showers through Monday. The low will
continue its trek southwest and will be near Adak by Monday
afternoon.

-JAR

&&

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

A well developed upper level Southern Bering low weakens as it
migrates into the North Pacific through the forecast period.
Forecast models are clustered initially but the GFS accelerates
into the the North Pacific through late Tuesday. However the
ECMWF, UKMET and CMC catch up to the GFS by Thursday, and maintain
good confidence in tracks and strengths throughout. The Eastern
Russia ridge lingers over Northwest Alaska and extends over the
Western Aleutians, while the ridge over Southeast Alaska builds
into the Interior through the week. This continues the cold and
dry conditions over most of Mainland Alaska. Outflow winds less
than gale force increase the cold air over the Bering, bringing
widespread freezing spray over most of the Central and Eastern
Bering.

A moderately developed surface North Pacific low approaches the
Central Aleutians for Tuesday. Snow is expected to spread across
the Aleutians and Alaska Peninsula into the Bering through
Tuesday. Continued warm moist air changes the snow to rain as the
precipitation extends over the AKPEN, Kodiak Island and into
Southwest Alaska by Wednesday, and the coastal Southcentral zones
through Thursday. Areas of snow infiltrate further inland,
especially over the higher elevations.

&&

.AVIATION...

PANC...VFR conditions and light northerly winds mostly under 10
kts will persist.

&&