Gale Warning 154, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
445 PM AKST Wed Feb 15 2023

.ANALYSIS AND UPPER LEVELS...

An amplified pattern persists across the region with the jet
stream tapping into sub-tropical moisture and crossing the
central Aleutians and then bending over the ridge near Southwest
Alaska before diving southward across the Gulf. Two shortwaves are
crossing Southcentral with the first producing light snow across
the western Kenai Peninsula. This snow will end this afternoon. A
second shortwave is moving east into the Yukon and Southeast
Alaska pushing the snow east of the area. Out west an occluded low
pressure system is west of the chain with the occluded front
stretching from the northern Bering through the eastern Aleutians.
This is producing gales across the Bering and central and eastern
Aleutians with blizzard conditions across the Pribilof Islands.

&&

.MODEL DISCUSSION...

Models are in decent agreement with the general synoptic scale
pattern, but are struggling with some of the details. There are
some model differences as the next storm force low moves across
the central Aleutians and towards Southwest Alaska Thursday and
Thursday night with the GFS the farthest south of the bunch, while
the GEM is farthest north and the EC somewhere in between. The
main challenge with this low is how strong the winds will be and
if high winds are possible. Also depending on the track of the low
will influence whether or not the Pribilofs will get strong winds
and blizzard conditions on Thursday. Across the east, models
differ on the movement of a triple point low forming along the
front near the southern tip of the Kenai Peninsula Friday morning.
The GEM models suggest a track just east of the Kenai Peninsula
moving into Prince William Sound, while the GFS is farther south
as it moves into the northern Gulf with the NAM and EC in between
these solutions. The ensembles are also not helpful as they each
favor their respective deterministic solutions. The biggest
challenge this low will bring is the potential for increased snow
amounts for the Anchorage area if the low tracks into Prince
William Sound.

&&

.AVIATION...
PANC...VFR conditions and light winds will persist through
through tonight. Tomorrow morning an approaching shortwave trough
could possibly bring some light snow near the area with ceilings
decreasing to MVFR.

&&

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

Benign weather tonight and early tomorrow will transition towards
stormier weather Thursday night and Friday. Calm to light winds,
with the occasional light bout of snow, will persist across
Southcentral tonight as weak low pressure in the Gulf slowly
dissipates. Snow chances increase later tomorrow as an upper
level shortwave moves across Anchorage, the Mat-Su Valleys, and
Prince William Sound. This shortwave is weak, and guidance looks
to have trimmed back snow amounts a bit since the previous
forecast package. Any snow that does fall is expected to be very
light.

The main story in the short-term continues to be a triple point
low that develops near Kodiak Island Thursday night. Confidence is
high that this will be a moist system, with increasing confidence
that we'll see fairly strong winds, especially at elevation. This
system will first impact Kodiak island Thursday afternoon, with
precipitation initially starting as snow before transitioning to
rain. The front will quickly move into the north Gulf coast by
Friday morning, before exiting to Southeast Alaska by Friday
night. Snow will be moderate to heavy at times, especially along
Eastern Kenai Peninsula and Prince William Sound. A tight
pressure gradient will induce strong easterly winds through
Eastern Turnagain Arm and along the Anchorage Hillside. This could
create hazardous conditions along Eastern Turnagain Arm/Portage
Valley and in the Anchorage Hillside for early Friday morning.
Stay tuned as we continue to update the forecast and hone in on
these details. Otherwise, more snow could be on the way for
Saturday as yet another triple point low moves along the north
Gulf coast.

&&

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

A front moving in from the Bering Sea will reach the Southwest
coast tonight. A brief period of light snow is expected from the
front for the Kuskokwim Delta and the Bristol Bay coast before it
tracks farther inland and decays rapidly Thursday morning.
A stronger system will approach the Southwest coast Thursday
afternoon and begin to move inland Thursday night. This stronger
front is expected to bring more substantial snow and gusty
easterly winds across much of Southwest Alaska. There will be
some potential for blowing snow, especially along the coast,
though temperatures are expected to increase into the 30s rapidly
in Bristol Bay. The Kuskokwim Delta looks more ripe for more
blowing snow, with temperatures expected to remain cooler for
longer. A Winter Weather Advisory has been issued for this risk.
Snow totals from this system will range from 3 to 6 inches for
most locations, and the bulk of this snow will accompany the front
Thursday night. As the low moves inland over the Kuskokwim Delta,
winds will shift out of the southwest and are likely to reach
gale force along the coast. Light snow showers are expected to
accompany this onshore push, but they could be widespread enough
in the Kuskokwim Delta for blowing snow and low visibility to
stick around through Friday afternoon. Winds will ease through the
day Friday as the low exits to the north. Then, a low tracking
along the Alaska Peninsula looks to bring more snow to Bristol Bay
for Saturday.

&&

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

A strong front extending off a deep low in the far western Bering
Sea pushes east to the Southwest coast this evening. Gusty
southerly winds wrapping around the low center will continue for
the western Aleutians as the low tracks slowly northeast through
Friday. Further east, the forecast is complicated. Models continue
to have a significant spread with a low expected to develop near
the central and eastern Aleutians Thursday morning. This
introduces significant uncertainty with regards to its impacts.
There is significant potential for high winds in association with
the developing low, but the placement is still uncertain at this
time. They will have the potential to occur on the south side of
the low through the eastern Aleutians and southern Alaska
Peninsula with cold air wrapping around the back side of the low
and rapid pressure rises in its wake. The likelihood of high
winds increases further east as the low strengthens along its
track, though high winds are less favored along the Alaska
Peninsula due to terrain blockage with a southwesterly wind
direction. A High Wind Watch has been issued for the eastern
Aleutians due to the remaining uncertainty. Precipitation will
largely be rain with this system along the Aleutians, though some
snow will be possible at the onset and as snow showers in the
colder air mass behind the front. Snow is likely for the Pribilof
Islands as the center is now expected to track east of the
islands. Winds decrease below gale force across most of the
region by Friday night as the low tracks up the Western Alaska
coast. By Saturday, the Aleutians/Bering Sea will be under the
influence of a cold air mass aloft as the former hurricane force
low weakens over the western Bering. This will keep the region in
a showery regime going into the weekend.

&&

.LONG TERM FORECAST (Days 4 through 7: Sunday through Wednesday)...

A broad upper level ridge is expected to move over Southcentral
and Southwest Alaska during the extended period. Ensemble guidance
shows consistency in the ridge-axis extending across the lower
Kuskokwim Valley and across the western Alaska Range. The
orientation of this ridge supports a moderate tilt in the odds in
favor of warmer than normal temperatures and above normal
precipitation across Southwest Alaska. The odds also show a slight
tilt in favor of below normal temperatures across the Copper
Basin, with the strength of the tilt increasing farther east.

Synoptically, a frontal system is likely to move over Southwest
Alaska on Tuesday, though confidence remains low on the position
and orientation of the front at this time which results in low
confidence in the precipitation and precipitation type forecast.

The other concern this forecast period is strong westerly gap flow
through bays and passes across the western Gulf of Alaska on
Monday and Tuesday. Heavy freezing spray will likely be associated
with these strong gap winds due to cold air advection being
expected at the same time.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...High Wind Watch 185. Winter Weather Advisory 155.
MARINE...Gale 130 132 150-170 172-178 180-185.
		 Storm 171 179.
		 Heavy Freezing Spray 130 139 140 155 180 185.
FIRE WEATHER...NONE.

&&

SYNOPSIS AND MODEL DISCUSSION...RC
SOUTHCENTRAL ALASKA...KC
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...CQ
LONG TERM...ED