Heavy Freezing Spray Warning 174, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
445 AM AKST Fri Nov 19 2021

.ANALYSIS AND UPPER LEVELS...

A large upper level low is continuing east along with a weakening
surface low heading towards the Southeast Panhandle. Gap winds
due to the tightened pressure gradient along the Gulf coast are
also weakening gradually as reinforced cold air advection slowly
mixes out. A North Pacific low is strengthening and moving into
the western Gulf. A compact surface low is located over the
western Aleutians moving east and bringing moderate rain to the
region.

&&

.MODEL DISCUSSION...

Overall agreement points toward a new weather pattern developing
this weekend. A North Pacific low will move northward and is
expecting to interact with the Aleutian low. Once the Pacific low
reaches the Aleutians and Western Gulf into Saturday morning,
models align with this North Pacific low becoming the dominant
system and the Aleutian low decaying. The low will move south of
Kodiak Island before elongating and track towards the Northern
Gulf.

Snow totals for Kodiak indicate some model disagreement and
forecast confidence is uncertain. The resulting depth and any
nudges of the low centers to the east or west could influence the
placement of the warm sector and the precipitation totals through
the weekend. Precipitation along with gust easterly winds are expected.
Precipitation type also remains somewhat uncertain. The models
predominantly indicate snow due to colder air aloft, however
given the warm sea surface temperatures and the long fetch over
warmer water streaming into Kodiak, brief periods of mixed
precipitation remain possible.

Towards the end of the weekend when this low tracks into the
Northern Gulf, confidence is high for stronger easterly winds to
develop near the coast ahead of its associated front. The
duration and timing of precipitation will depend on the exact
position of the low center.

&&

.AVIATION...

PANC...VFR conditions and light winds will continue through
Saturday morning.

&&

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

Conditions will remain clear and very cold across much of
Southcentral through Friday with high pressure anchored over the
Al-Can border. A broad trough will linger across the northern
Gulf this morning, allowing for gap winds to continue. These
winds, however, have waned overnight and will continue to trend
downward through the day as both the trough and surface low east
of the Copper River Delta weaken.

The pattern then begins to get more active for the weekend as a
North Pacific low lifts north toward Kodiak Island. This feature
will lift a front across the Gulf with snow developing for Kodiak
Island and Kodiak City by mid-morning Saturday. Northeasterly winds
along the front will quickly ramp up as well, with gusts over 50
mph expected along the eastern coast of Kodiak Island. Recent
model runs have come into better agreement with regard to the
track of this system, but the question of just how much influence
the warm sea surface temperatures will have on the surface
temperatures for locations such as Kodiak City remains uncertain.
Guidance briefly stalls the low south of Kodiak Island before
moving it northeast near Middleton Island by late Sunday. This
track will likely keep winds along the Kodiak Island coast more
north-northeasterly, allowing colder air to remain in place.
However, with sea surface temperatures hovering between 40 and 42
degrees, any prolonged northeasterly flow may drive temperatures
in Kodiak City from the lower 30s into the mid 30s and allow for
at least a mix of rain and snow, if not a complete changeover to
rain by Saturday afternoon. Even with the uncertainty in max
temperature, there will likely be a period of snow in conjunction
with strong winds during the onset of the event and again toward
the end of the event as colder air wraps in behind the low. The
combination of snow and wind could reduce visibilities at times
due to blowing snow. Kodiak City could see upwards of 6 inches of
snow with this event, with lesser amounts if any rain does mix
with snow.

The front moves north by early Sunday morning with snow
developing along the Southcentral coast. Snow with gusty winds are
likely for Cordova with snow and blowing snow likely for Thompson
Pass. Again, snow amounts in Cordova will be dependent on how
much warmer, marine air advects over the immediate coast. The
precipitation will linger through Sunday for Cordova and Valdez,
with snow developing across the Copper River Basin and eastern
Kenai Peninsula by late Sunday morning. While a few inches of
snow are possible across the Copper River Basin, upwards of a foot
or more of snow is possible for Whittier and Portage Valley. Snow
will continue for these locations through Monday with snow
possibly overspreading the Anchorage Bowl and western Kenai
Peninsula.

&&

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

A quiet and cold pattern will continue across Southwest Alaska
over the next few days as the dry and cold offshore flow pattern
continues. Radiational cooling is expected to continue across the
lower Kuskokwim Valley during the nocturnal hours as clear skies
and light winds will continue. Temperatures will be slightly
warmer over the Kuskokwim Delta due to brisk northeasterly winds.
Nighttime low temperatures will range between -10F and -20F across
the lower Kuskokwim Valley, 0F and -10F across the Kuskokwim
Delta and 0F and -5F across Bristol Bay.

&&

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

An active weather pattern continues across the Bering/Aleutians as
a gale force low continues to linger around the central Aleutians.
Widespread areas of gale force winds will continue across the
central and western Bering Sea today and tonight. Winds will begin
to gradually ease to below gale force across the western and
central Bering Sea Saturday morning as this low moves
southeastward into the North Pacific. Winds will strengthen across
the coastal waters south of the Alaska Peninsula and eastern
Aleutians on Saturday as this low strengthens while moving into
the Gulf. Large long period swell in the central Bering will
gradually avate on Saturday due to the easing of the easterly
winds. Widespread gale force winds with localized areas of storm
force winds are likely across the coastal waters south of the
Alaska Peninsula on Saturday and Saturday night before gradually
easing on Sunday.

&&

.MARINE (Days 3 through 5: Saturday through Monday)...

Gulf of Alaska... A front with a triple point low is expected to
move into the Gulf with gale force winds across the southern Gulf
by Saturday morning. Sunday this system will move across the
northern Gulf with gales possible across the Gulf. Monday the low
will weaken with winds small craft or less across the area.
However, there is a lot of uncertainty of the strength and track
of the low in the Gulf Saturday through Monday. Seas will remain
below 20 feet.

Aleutians/Bering...A front will stall across the southern Bering
on Saturday with gales expected along and north of the front.
These winds will weaken Saturday night and Sunday to small crafts
and less. Meanwhile, a low will track south of the Aleutian chain
Saturday and towards the north Pacific by Sunday. Expect gales
north of the low along the Aleutian chain and the AKPen on
Saturday weakening to small crafts or less by Sunday. By Monday
another north Pacific low moves south of the Aleutians spreading
gales along the western and central Aleutians. Seas will remain
below 20 feet.

&&

.Long Term Discussion (Days 4 through 7: Sunday through Wednesday)...

There is increasing model spread for the extended period, largely
due to differences in interaction between an Arctic trough digging
southward across mainland Alaska and a trough crossing the North
Pacific and headed toward the Gulf of Alaska. The key will be
timing and spacing of these troughs, which will determine whether
they remain separate or whether they interact, with phasing of
short-waves. The commonality in all solutions is the development
of a very large closed upper low centered over Southwest Alaska.
So, what does this mean for the weather. Arctic air will be firmly
entrenched across much of Alaska, including the Bering Sea and
Aleutians. The storm track will be centered across the North
Pacific and into the Gulf of Alaska. Depending on the evolution
of the upper level pattern, storms crossing the Gulf could impact
Southcentral (which would also moderate temperatures) or they
could remain farther south and track toward Southeast Alaska.
For now, based on ensemble guidance, will keep most of the region
cold and dry, with the best chance of precipitation across Kodiak
and the Gulf coast.

&&
.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...Wind Chill Advisory: 131 135
MARINE...Heavy Freezing Spray: 119 127 139 140 160 180 181
		 Storm Warning: 131 132 136 138 150 351 352
		 Gale Warning: 119 120 127 130 137 139 155 165 177 179 185
					   411-414
FIRE WEATHER...NONE.

&&

SYNOPSIS AND MODEL DISCUSSION...VR/AP
SOUTHCENTRAL ALASKA...TM
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...ED
MARINE/LONG TERM...CJ/SEB