Gale Warning 127, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
600 AM AKST Wed Feb 8 2023

.ANALYSIS AND UPPER LEVELS...

Multiple weak upper level waves and surface lows continue to
rotate around a negatively titled trough axis stretching from the
Bering Strait and into the Gulf of Alaska. A few of these waves
within the trough is moving north from the Gulf to Southcentral,
leading snow showers mainly along the southern half of the region.
For Southwest Alaska, relatively quiet weather with areas of
stratus over the Kuskowim Delta, while clear skies and strong
radiational cooling elsewhere allowed overnight temperatures to
drop down below freezing. Out west, a few transient lows continue
to move through the Bering Sea and Aleutian Chain.

&&

.MODEL DISCUSSION...

Model guidance is in good agreement with the placement and
intensity of synoptic scale features at both the surface and in
the upper levels. The main challenge is the timing of these
aforementioned waves and snowfall amounts across Southcentral.
Out west, the deterministic model runs are decently clustered
with a strong North Pacific low approaching the Aleutian Chain
between Thursday and Friday.

&&

.AVIATION...
PANC...Light snow showers will continue through midday with
intermittent MVFR conditions. Snow accumulation through today
will be about half an inch. VFR conditions with light winds are
expected around 09/03z when precipitation tapers off.

&&

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

A negatively tilted upper-level trough extending from the Alaska
Peninsula across the Kenai Peninsula and northern Gulf this
morning will slowly lift to the Copper River Basin by Thursday
morning. A complex low with centers of circulation east of Seward
and east of Kayak Island will also move northward in response to
the progression of the upper-level wave. The low near Kayak Island
will continue to bring snow showers from Valdez to Cordova this
morning before moving over the coastal mountains and dissipating
this afternoon.

The low currently east of Seward will maintain its strength as it
moves into western Prince William Sound. This low will then
weaken into an open wave and eventually dissipate later this
afternoon. Moisture associated with this low will get caught up in
the southeasterly flow ahead of the upper-level trough and lift
across northern Cook Inlet, the Anchorage Bowl, and Mat-Su Valleys
this morning. Widespread light snow has already begun to
develop across these areas, and will persist as the trough moves
closer to the region. The snow will come to an end for these areas
by Wednesday evening. Scattered snow showers, however, may linger
across the higher elevations into early Thursday morning. A
general 1 to 3 inches of snow, with isolated higher amounts, is
expected with this system.

As the trough moves away, a northerly flow in the mid and upper
levels will develop, ushering in a colder and drier airmass. The
combination of colder air, developing high pressure inland, and a
surface trough lingering over the northern Gulf, will allow for
the development of gusty offshore winds, especially along the
immediate coast and for favored channeled areas such Seward and
Whittier. These winds are expected to develop by late Wednesday
evening, peaking Thursday morning through Thursday afternoon
before slowly winding down overnight Thursday into Friday.

The change in airmass to a colder and drier one will also result
in colder temperatures across the region for the latter half of
the week. Temperatures are expected to bottom out overnight
Thursday into Friday morning with lows reaching 0 to 15 degrees
along the coast to 0 to 20 below zero for interior locations. The
biggest challenge concerning low temperatures will be whether any
low stratus or fog lingers in Cook Inlet and the Copper River
Basin in the wake of the trough.

&&

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

Quiet weather today will become increasingly active as we head
into Thursday and Friday. For today, expect patchy clouds and
cold temperatures to persist across Southwest Alaska. An upper
level low lingering just off the coast of the Yukon Delta may
bring some isolated to scattered snow showers to the region,
though precipitation chances generally remain low. Snow chances
increase Thursday morning as a shortwave trough tracks west to
east across the region, bringing light snow mainly along eastern
Bristol Bay and the Western Alaska Range.

By Thursday afternoon, a 950 mb low tracking along the Aleutian
Chain begins to make its presence felt. A High Wind Watch is in
effect for the Alaska Peninsula, especially near Cold Bay, as
the low pushes its front into Southwest Alaska. Moderate to heavy
precipitation along this front, in conjunction with strong winds,
could lead to blowing snow and reduced visibilities. There remains
some uncertainty with how strong winds will gust, and how quickly
snow is expected to change over to rain. However, there is high
confidence that this will be a rather windy and wet system. The
Alaska Peninsula will see the brunt of winds and precipitation,
especially as the system weakens as we head into Friday. However,
winds will still be a concern for the Kuskokwim Delta and the
western portion of the Lower Kuskokwim Valley as cold air
advection in combination with northerly winds could lead to wind
chills dipping into the -30s and potentially the -40s.

&&

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

Various weak lows spinning around the Bering Sea and Aleutian
Islands today may lead to localized areas of elevated winds and
snow showers. The big story, however, will be a 950 mb low moving
north towards the Central Aleutians by Thursday morning, then
west along the Aleutian Chain through Friday. Multiple products
are out for this system, including a High Wind Warning for the
Central Aleutians, a High Wind Watch for the Eastern Aleutians,
and a Winter Storm Watch for the Pribilof Islands. Moderate to
heavy precipitation with this system may lead to reduced
visibility if snow falls in conjunction with these strong winds.
Uncertainty remains with precipitation type transitions,
especially where temperatures hover near freezing for the Central
Aleutians, so confidence is low to moderate regarding blowing snow
potential along the Chain. In addition to these land-based
hazards, northerly flow and cold air advection through the
northern Bering Sea may lead to heavy to extreme freezing spray
along the ice edge. Overall, numerous hazards are expected from
Thursday through Friday. Please stay tuned as we continue to
refine and update the forecast.

&&

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

A progressive, amplified pattern is expected to keep active
weather ongoing across southern mainland Alaska this weekend into
next week. The weekend looks to begin with low pressure in the
Gulf of Alaska, with a front initially bringing heavy
precipitation decaying and turning showery. Another low enters
the Gulf on Saturday, reinforcing low pressure and bringing
another round of heavier precipitation along the coast by
Saturday night. The track of the low will serve to keep much of
the precipitation from moving inland, and with little warm air
making its way into the mainland. However, models indicate a weak
front may bring light snow on the back side of the low over
Southwest Alaska for Sunday, moving into Southcentral by Monday,
but the light nature of the precipitation is expected to limit
snow amounts to just a few inches. Cold air, as cold as -24C at
850 mb, moves in over the Bering Sea and Southwest Alaska on
Sunday, cooling temperatures at the surface and helping to drive
strong gap winds on the south side of the Alaska Peninsula and
along the western Gulf. These winds are likely to gust to storm
force, and in localized areas storm force winds may be sustained.
Gap winds diminish going into Monday as the low pressure in the
Gulf weakens. Shower activity decreases along the north Gulf coast
as a result, and the decaying front leaves much of the southern
mainland dry by Monday night.

At the same time, a strong storm force, or potentially hurricane
force, low in the North Pacific approaches the Aleutian Islands.
Current model consensus suggests that the low tracks several
hundred miles south of the islands, but its front pushes across
the central and eastern Aleutians on Monday. This may bring
easterly winds as strong as storm force along with snow, as a
colder air mass remains in place over the Bering. Snow moves up
along the Alaska Peninsula into Bristol Bay and over Kodiak Island
on Tuesday. While the low dips back into the North Pacific, a
southerly oriented warm conveyer belt brings a continued push of
moisture to fuel precipitation. Transient high pressure enters
the Bering Sea on Tuesday within a very amplified pattern, which
will bring drier conditions. Then, a strong front off a deep low
near the Kamchatka Peninsula looks to bring rain to the western
Aleutians on a southerly push of warmer air late on Tuesday.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...High Wind Warning 187
		 Winter Storm Watch 195
		 High Wind Watch 181, 185
MARINE...Heavy Freezing Spray Warning: 180, 185
		 Storm Warning: 172-176
		 Gale Warning: 155, 170-171, 177, 179
FIRE WEATHER...NONE.

&&

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