Small Craft Advisory 241, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
437 PM AKDT Tue Mar 21 2023

.ANALYSIS AND UPPER LEVELS...

A broad long-wave trough with embedded shortwaves extends from
the Kamchatka Peninsula into Southcentral Alaska. The two
shortwaves of note to the weather today exist just south of the
Prince William Sound, with a stronger feature moving over the
eastern Aleutians and Alaska Peninsula this afternoon. The
northern Gulf low has been sending bands of light snow into the
coast today, but is rapidly weakening. The stronger western low
continues to intensify as it moves east, with strong winds and
snow impacting the eastern Aleutians and Alaska Peninsula this
afternoon. To the west of the low, cold air advection in a
westerly flow regime has created a broad area of snow showers.

&&

.MODEL DISCUSSION...

Models are in good synoptic agreement through 24 hours before they
begin to diverge. The most notable difference is in the low track
starting at 12Z Wednesday as a compact low moves over or just
south of Kodiak Island. This track will have implications for the
snow and blowing snow forecast for the western and northern sides
of the Island at the system tracks to the east. There are also
some differences in the speed as the front lifts north through the
Gulf Coast and Prince William Sound, which will have an impact on
snow totals.

&&

.AVIATION...

PANC...VFR conditions will persist. Gusty northerlies will develop
in the morning Wednesday in response to a low moving into the
Gulf.

&&

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

Snow showers are ongoing across Eastern Prince William Sound down
to Kayak Island this afternoon. What remains of an occluded low
and front will push inland of the coast through this evening and
ultimately dissipate. The rest of Southcentral has enjoyed largely
clear or partly cloudy conditions from the Susitna Valley into
the Copper River Basin while under a transient ridge of high
pressure. On satellite the next snow maker is quickly approaching
Kodiak Island from the south. A triple point low is in the process
of forming south of the Alaska Peninsula and will move over
Kodiak Island tonight through the morning hours on Wednesday. A
threat for snow and blowing snow is expected as the low departs to
the east of the region, with increasing northwesterly winds
developing over the Shelikof Strait. Locations could see anywhere
from 3 to 5 inches of snow coincident with gusts of up to 50 mph.
Despite warmer temperatures, visibilities would likely be reduced
to one half mile or less at times, especially for Kodiak Island's
western coastline. A winter storm watch is currently in effect for
the area, as some questions do remain with how far north the
surface low will lift across Kodiak Island before shifting east
and into the Gulf. While not currently forecast, any further
northward movement of the low would bring increased snow amounts
and wind to the city of Kodiak and potentially into Kachemak Bay.
However, it should be noted that models have been trending the
opposite direction, with the surface low remaining further south
and east of Kodiak City.

Low pressure center then continues eastward into the offshore
regions of the Gulf while its front moves into the Kenai Peninsula
and Prince William Sound through the morning hours on Wednesday.
A blizzard warning is in effect for Western Prince William Sound
and the Eastern Kenai Peninsula. Easterly winds gusting into the
40's and 50's are anticipated on top of moderate to heavy snow.
Areas from Whittier into Portage into Turnagain Pass could see a
foot or more of snow through Wednesday. Locations further south
along the Seward Highway are expected to see more modest snow
amounts of 6 to 12 inches, while locations closer to Girdwood may
see snow amounts of 5 to 7 inches. In addition to snow winds will
be active through the Eastern Turnagain Arm and across the Seward
Highway Corridor. Winds gusting as high as 50 mph could
significantly reduce visibility down to one quarter of a mile or
less, which will make for hazardous driving conditions for those
on their morning commute on Wednesday.

For Thursday, snow showers are expected to linger over the
eastern mountain faces as the Gulf low maintains elevated
southeasterly flow into the Gulf coast. Strong easterly flow aloft
should downslope much of the precipitation out for locations
further inland. The Anchorage Bowl may see a brief bout of light
snow as winds relax on the tail-end of the departing Gulf low.
Attention then turns to Friday where a shortwave trough digging
into Southcentral may see snow chances increase again from the
Susitna Valley into the Copper River Basin.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (through Friday morning)...
A low pressure system traversing the Alaska Peninsula and
strengthening Tuesday evening will bring active weather to the
area through early Thursday. Snow will overspread the Alaska
Peninsula Tuesday evening as winds rapidly increase across the
area. Some snow will spread over into the Greater Bristol Bay
area, but the majority will be along the Peninsula. In general
expect most areas to be in the 1-3 inch range with some areas
along the Alaska Peninsula in the 3-6 inch range. Blowing snow is
also an issue mainly from Pilot Point through Naknek, but there
may be enough open water within the ice pack to mitigate some of
the blowing snow as well as keeping temperatures a tick warmer. A
deformation band looks to form over Dillingham through Pilot Point
and progress northeastward through late Wednesday bringing some
light accumulating snow to most areas. A late season colder air
mass comes onto the mainland behind this system for the remainder
of the week. Thursday looks to bring a quick shot of snow as a low
forms near the ice edge and move toward the Y-K Delta.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (through Friday morning)...
A low transiting across the Alaska Peninsula into the Gulf of
Alaska is spreading a late-season arctic air mass over the Bering
which will bring widespread gales and snow showers through
Wednesday. Model guidance is hinting at a possible polar/hybrid
type low to form along the ice edge. These are usually compact
with a small but intense wind field, usually gales or greater. The
amount of upper dynamics should push this eastward toward the
mainland quicker than would normally happen. A stronger western
Bering system will bring a front and southerly winds on Friday,
likely gales with the possibility for storms.

&&

.LONG TERM FORECAST (Days 4 through 7: Saturday through Tuesday)

A transient, but amplified ridge will build into Southcentral
Saturday bringing quieter weather through Sunday before another
Bering Sea front approaches in the latter half of Sunday and into
Monday. This creates another problem with possible precipitation
for Southcentral heading into the week due to the development of a
possible surface low in the Gulf. Models have been struggling to
define what exact impacts this aforementioned low will have. Out
west, conditions along the southern half of Bristol Bay and the
Alaska Peninsula should remain fairly quiet through Saturday.
Northern parts of Bristol Bay into the Kuskokwim Delta region
could get clipped by a Bering low pressure system's warm- front
the latter half of Friday into the day on Saturday, which paves
the way for light precipitation chances. The cold- front of this
Bering low will track into the western Bering and western
Aleutians Friday making it to the Southwest coast by Saturday
night into Sunday morning. Accompanying this front will be gale-
force winds with possible storm-force gusts, especially for the
western Aleutians. As the front progresses eastward throughout the
central and eastern Bering, winds will weaken mostly to low- end
gales to high-end small craft through Sunday morning. Southwest
looks to become unsettled late Saturday night into the day on
Monday as the front will cross the southern mainland then. There
are still a few timing differences regarding the progression of
the front through Southwest. However, the progressive pattern
looks to continue with no real sustained breaks in activity.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...Blizzard Warning 125.
		 Winter Storm Watch 171.
MARINE...Storm Warning 734 751 755.
		 Gale Warning 710 711 712 715 716 724 725 726 730 731 733
					  732 738 742 750 752 753 754 756 757 758 759
					  770 772 771 773 774 775 776 777 778 780 781
					  782 783 784 766 760 761 762 764 411-414
					  351-352.
		Heavy Freezing Spray Warning 760 761 762 764 767.
FIRE WEATHER...NONE.

&&

SYNOPSIS AND MODEL DISCUSSION...CJ
SOUTHCENTRAL ALASKA...BL
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...ML
LONG TERM...NS