Gale Warning 848, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
519 AM AKST Sun Dec 25 2022

.ANALYSIS AND UPPER LEVELS...

Low pressure centered just off the coast of Bristol Bay shifts to
track westward across the Bering Sea towards the Western Aleutians
into early next week. Longwave troughing extends into southwestern
Alaska. Resultant snow across Bristol Bay can be seen on Radar,
with the edge of the snow band sitting over Dillingham, and
increased winds across the region have been observed throughout
the night. Meanwhile, a North Pacific low makes its way towards
the western Gulf of Alaska. As it reaches near Kodiak Island, it
begins to mesh with the Bering Sea low, becoming an elongated
trough in the upper levels. The surface reflection at the base of
the upper trough will become relatively stagnant, sitting east of
the Barren Islands through Tuesday afternoon. There will be a
tightening of the pressure gradient in the Mat Valley Sunday
afternoon through Monday morning, leading to another round of
windy conditions.

Shifting gears back west, the Bering low reaches the Western
Aleutians late Monday night, where it will begin to interact with
a second North Pacific low. The systems will Fujiwara around
each other, with the initial low being pulled into the North
Pacific and the second low being shunted off towards the Eastern
Aleutians.

&&

.MODEL DISCUSSION...

Models remain in good overall synoptic agreement through the short
term. There remains some light discrepancies towards as the Bering
Sea system begins to interact with another incoming North Pacific
low. The main forecast challenge will be winds through the Mat
Valley as the pressure gradient tightens Sunday afternoon into
Monday morning.

&&

.AVIATION...
PANC...VFR conditions will persist. Gusty northerly winds will
continue throughout the day.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 through
3/Christmas Day through Tuesday night)...

Area of light snow persists this morning across the eastern Kenai
Peninsula, due to the combination of a weakening inverted trough
and the easterly flow aloft providing a moisture tap running up
against the coastal mountains. Elsewhere, conditions are generally
quiet this morning. A surface ridge over the Al-Can continues to
keep colder air locked in place over the interior. However,
temperatures are moderating slightly as cloud cover increases from
south to north.

The increase in cloud cover is associated with a mature low over
the north Pacific and its associated occluded front lifting north
into the Gulf of Alaska. Both feature will move north today, with
widespread precipitation and easterly storm-force winds
developing out ahead of the front. Expect strong winds and a
rain/snow mix changing quickly to rain for Kodiak City later this
morning, with precipitation moving to the Southcentral coast by
afternoon. Precipitation is expected to begin as all snow, but
will transition to rain for Whittier and Portage Valley by tonight
as the stout easterly flow and gusty southeasterly surface winds
usher in much warmer air, with temperatures pushing above freezing
for Whittier, Seward, and Portage. Snow will also quickly
changeover to rain for Cordova as gusty east winds drive in warmer
air. For Valdez and points north, temperatures should stay cold
enough for all snow, as the surface front stalls along the coast.

The strong cross-barrier flow will likely limit precipitation
changes along the lee of the Chugach and Kenai Mountains. However,
there is the change for some moisture to spill over, resulting in
flurries or periods of very light snow for Kenai to Anchorage and
Talkeetna later today. With warmer air moving in aloft, there is
also the potential that some very light freezing rain may mix in
with snow around Homer and along the southwestern Kenai Peninsula
coast. Any freezing rain/drizzle is expected to be light and not
result in any impacts.

A fairly active pattern will continue over the next few days
across Southcentral Alaska. Low pressure will move into the Gulf
on Sunday and will result in widespread gale force winds with
areas of storm force winds in the northern Gulf. These winds will
gradually ease as the low lifts northward through Monday night.
The biggest forecast challenge is snowfall amounts and
precipitation type across Kodiak Island and along the southern
coast of the Kenai Peninsula. The precipitation is likely to be
confined to the windward side of the mountains due to strong
downsloping on the leeward side as a result of strong cross
barrier flow.

The other concern will be an increase in gusty winds across the
Matanuska Valley beginning later today. Gusts are expected to
peak between 50 and 60 mph Sunday night through Monday morning
before slowly diminishing for Tuesday.

Precipitation will persist along the coast through Tuesday as the
front stays put and the the low slowly moves north toward the
southern tip of the Kenai Peninsula.

Temperatures will continue to warm through the period, reaching
near or slightly above normal by the start of next week.

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

The upper low and surface meso will continue to move west and out
of the region this morning, bringing an end to snow for most
areas today. A strong low currently in the north Pacific will move
towards Kodiak Island late tonight, with some overrunning snow
expected for Bristol Bay and the Alaska Peninsula (AKPen). The
associated upper level feature will quickly break apart at it
interacts with ridging over the interior and the dominant upper
low over the central Bering. As a result, precipitation will have
a hard time making it far inland. Easterly flow off the mountains,
in combination with warm air advection, will create a potentially
above freezing layer aloft from Egegik to Iliamna through Monday.
This layer isn't expected to be particularly deep, so sleet may
mix in with any snow that manages to overcome the downsloping. On
Tuesday, cold air advection will move back in from the Bering,
which will help to negate this problem for any remaining
precipitation. Generally speaking precipitation is expected to be
very light over the coming days.

&&

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

A tight upper low between St. Paul and Nunivak Island this morning
will expand and become in dominant feature in the Bering for the
coming days. Light and intermittent snow will continue for most of
the Chain and Pribilof Islands through Monday, with ample cold air
continuing to move south through the Strait and off of western
Alaska. An additional system will move north towards the Aleutian
Chain on Tuesday, returning rain and stronger southeasterly winds
to the central and eastern Aleutians.

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

The overall pattern for the first half of the extended outlook is
likely to remain about the same, with a broad Aleutian low
drifting slowly along and south of the Aleutian Chain out west
through at least Friday. A loosely-defined longwave trough will
persist aloft across the Bering, resulting in an unsettled pattern
out west with gusty winds likely in gale force range wrapping
around the main low at the surface near the southern Bering on
Wednesday and Thursday. Light onshore flow over Southcentral
should keep any areas of snow and coastal rain confined near the
Prince William Sound, eastern Kenai Peninsula and across Kodiak
Island, with most inland areas remaining dry and seasonably mild.
Very weak steering flow again should result in very slow
progression of both the larger scale pattern and smaller waves
rotating around the Bering trough/low, with the vast majority of
the Pacific jet likely to remain well south of the outlook area
until the end of the week. This weak steering also causing models
to struggle with the handling of smaller scale features, with the
details for individual perturbations really falling apart by
Thursday and Friday.

There are some early indications for a shift in the pattern to
commence by Saturday, as the low meandering near the Aleutians
finally begins to shift into the western Gulf and amplifies the
upstream ridge over the Gulf and portions of Southcentral. This
could result in much heavier precipitation spreading along the
coast between Kodiak and the Prince William Sound by this weekend.
However, large model spread by this point in time still leaves
much of the remaining details left to be determined.

&&
.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...Winter Weather Advisory: 131 195
MARINE...Storm Warning: 119 120 130 131 138 185 351
		 Gale Warning: 125 127 128 132 136 137 139 140
					   150 160 181 352 411 414
		 Heavy Freezing Spray Warning: 139 140 160 180
									   181 412 414
FIRE WEATHER...NONE.

&&

SYNOPSIS AND MODEL DISCUSSION...KM
SOUTHCENTRAL ALASKA...TM
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...CJ
LONG TERM...AS