Gale Warning 156, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion...CORRECTED
National Weather Service Anchorage AK
852 AM AKST Thu Feb 16 2023

.ANALYSIS AND UPPER LEVELS...

An amplified pattern continues across the region with a
southwesterly 157 kt jet draped across the central Aleutians and
riding along the peripheral of a ridge located over Southwest.
This jet stream is drawing substantial sub-tropical moisture from
the Pacific and pulling it northwards across the central Aleutians
and Pribilof Islands today and will eventually work its way into
Southwest Alaska this evening/tonight. Winter Weather Advisories
for the Kuskokwim Delta and for Bristol Bay, north and west of King
Salmon have been issued as a result, see the short- term forecast
for Southwest Alaska for more information. Meanwhile, a front is
noticed on radar tracking into the Southwest early this morning
with light snowfall reported along the coastline.

Out east, low stratus and patchy fog is being observed on
Nighttime Microphysics across the Copper River Basin, portions of
Knik Arm, and western Kenai peninsula. Higher-level clouds are
also noticed spanning across Kodiak and making their way northward
clipping the Kenai Peninsula early this morning as an occluded
front traverses through the area.

&&

.MODEL DISCUSSION...

Models continue to be in decent agreement with synoptic scale
features, but are still struggling with the finer details.
Consensus is that a triple point low will form along a front
pushing through Southwest near the southern tip of the Kenai
Peninsula Friday morning. However, model spread grows where the
aforementioned low will track. The GFS seems to be the outlier
with keeping the progression of the low low slower than other
models and deepening the low further south as well. The Canadian
seems to be the middle ground for the GFS and NAM and deepens the
low, but brings it further north towards Prince William Sound like
the NAM but not as extreme. The position of this low will impact
the overall winds and snow totals across Southcentral.

&&

.AVIATION...
PANC...A shortwave producing light snow showers and lower
ceilings will continue to produce MVFR to IFR conditions and will
persist through the morning. Ceilings should gradually increase
through the day with light northerly winds persisting.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 through 3: Today
through Saturday night)...

A short-wave moving over top of a building ridge will just clip
Southcentral today, producing some light snow primarily inland
over the Susitna Valley and Copper River Basin. A stronger short-
wave near the central Aleutians this morning, will amplify as it
tracks to Southwest Alaska this evening, then split with some
of the energy lifting northward across western Alaska and some
pushing into Southcentral and the northern Gulf late tonight
through Friday. Meanwhile, a surface low will form over the
eastern Bering, with a frontal system tracking eastward into the
Gulf. A triple point low will then develop and track somewhere
across the northern Gulf. The track of this low is the biggest
area of uncertainty in the forecast, so stay tuned as the wind
direction forecast for the northern Gulf coastal waters could
require significant changes, depending on whether the low hugs
the north Gulf coast or tracks further south over the Gulf waters.

Fortunately, this low track will have minimal impact on the
weather for Southcentral. The strength of the upper level short-
wave (despite splitting) combined with abundant moisture transport
and a shift in low level winds from southeasterly to southwesterly
as the system moves through will bring snow to all of Southcentral.
GUsty east to southeast winds will develop ahead of the frontal
system tonight, primarily affecting the eastern Kenai Peninsula.
With a cold airmass in place, snow will be fairly low density and
easily blown around. Thus, have issued a Winter Weather Advisory
for blowing snow, including the Seward Highway corridor. As snow
overspreads the region tonight, the strong cross barrier flow
will lead to some downslope drying, with flurries or very light
snow at best in the lee of the Kenai and Chugach Mountains.
However, flow will quickly shift around to southwest Friday
morning, which will then bring steady accumulating snow to the
western Kenai, Anchorage, and the Matanuska Valley. This storm
will move through fairly quickly, so snowfall amounts will
generally be light. Snow will taper off Friday afternoon and
evening.

The break will be brief as another short-wave takes a similar
track Friday night through Saturday night. This short-wave looks
quite a bit weaker, though there are a lot of similarities with
frontal system, triple point low, and evolution of low level
flow across Southcentral. Thus, expect another round of snow
for Southcentral Saturday through Saturday night.

&&

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

A surface front dissipates over the Kuskokwim Delta coast and
Bristol Bay coast this morning. The next system of note is an
upper-level trough and associated surface low that pivot across
Southwest Alaska beginning later today. The low will extend its
front across the Alaska Peninsula this afternoon before lifting to
the Southwest Mainland coast by this evening. Snow, gusty winds,
and reduced visibilities are expected to accompany the front as it
traverses the region, where degraded conditions will progress
inland from south to north through the night. Thus, Winter Weather
Advisories have been issued for the Kuskokwim Delta and Bristol
Bay, particularly north and west of King Salmon, for this evening
through Friday morning. The main front pushes north of the area
on Friday morning and steady snow will turn to snow showers while
visibility improves. The system will continue to exit into the
Northern Mainland for the remainder of Friday. On Friday
afternoon, another system is advertised to approach the Alaska
Peninsula from the North Pacific. The low feature will likely
track northward across the Southwest Mainland for most of
Saturday.

&&

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

A large low pressure system remains centered just to the west of
the Western Aleutians and Bering as it extends its front into
Southwest Alaska this morning. The low will very slowly drift into
the Western Bering through the short term period. A new low is
expected to develop near the Central and Eastern Aleutians today
and will bring precipitation and elevated winds to these areas, as
well as the Pribilof Islands. The low looks to track across the
Pribilof Islands this evening before lifting to the northeast to
the Southwest Mainland. On Friday afternoon, another system is
advertised to approach the Central and Eastern Aleutians again.
Model agreement with this feature begins to diverge beyond this
time, however there is general consensus for the low to enter the
southern Bering on Saturday morning.

&&

.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...Winter Weather Advisory: 125, 155, 161.
MARINE...Gale Warning: 119-120, 130-132, 138-139, 150, 155, 160,
		 			   165, 170-179, 185, 351-352, 411, 413.
		 Storm Warning: 180, 414.
		 Heavy Freezing Spray Warning:185
FIRE WEATHER...NONE.

&&

SYNOPSIS AND MODEL DISCUSSION...NSC
SOUTHCENTRAL ALASKA...SEB
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...AF
LONG TERM...ED