Gale Warning 738, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
537 PM AKST Sat Nov 19 2022

.ANALYSIS AND UPPER LEVELS...

The anomalous ridging continues to stretch from western Canada
into the interior of Alaska and then bends westward across
Southwest Alaska and the Bering Sea. This ridge is bringing mostly
clear and dry conditions however some high clouds are invading
parts of the ridge associated with a low pressure system over the
Gulf. The low in the Gulf continues to move northwest towards the
Kenai Peninsula. Radar is showing light to occasionally moderate
rain from Prince William Sound towards the eastern Kenai
Peninsula. Rain has also been observed at Kodiak City. This is
also producing stronger winds with Gales across the northern Gulf
and winds of 20 to 30 knots across Kodiak Island. Farther west a
low pressure system is spinning south of the central Aleutians as
it heads east. Around this low are a couple of shortwaves on the
southern side which will eventually move towards the Gulf by
Sunday and Monday. The low south of the Aleutians is bringing
areas of rain across the Aleutians and southern AKPen and winds
generally 25 knots or less across the Aleutian chain. Temperatures
vary widely across Southcentral with 40s near the Gulf coast and
20s inland towards Anchorage and the MATSU valleys. With the
strong inversion still over the area the hillsides and mountains
are warmer generally in the mid to upper 30s. The coldest area is
the Copper River Basin with single digits to below zero this
morning. Temperatures across Southwest Alaska are still above
normal in the 30s with 20s across the Kuskokwim Delta. Across the
Aleutians temperatures are in the 40s with upper 30s across the
AKPen.

&&

.MODEL DISCUSSION...

Models are in good agreement with the major synoptic features
especially through Sunday. However on Monday and Tuesday a couple
of shortwaves with surface fronts and/or lows will rotate into
the Gulf but models continue to disagree on the timing and
strength of these features. The big forecast challenge through
Sunday is precipitation types with freezing rain most likely
across the western Kenai Peninsula and Anchorage bowl with most
soundings indicating this precip type. Elsewhere the challenge
will be rain,snow or sleet. Whatever precip type that does fall in
these areas will generally be a tenth of an inch or less of liquid
equivalent.

&&

.AVIATION...

PANC...VFR conditions and light winds will prevail through the
TAF package. The one major concern is there is a threat of
freezing rain at the terminal by mid-day through the evening
hours (21-06Z) on Sunday, with the best chances during the
afternoon. Any accumulations of freezing rain are expected to be
less than a tenth of an inch.

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

A broad longwave trough with multiple embedded shortwaves will
slowly move itself over Southcentral through the short term
period. The first shortwave and attendant surface low is currently
south of Middleton Island and will move slowly towards the
Southern Kenai Peninsula over the next 24-hours before lifting
inland. This will continue rain over coastal areas with mountain
snow above ~2500 ft. As the shortwave lifts north, the end of
downslope flow and supportive upper level dynamics/shortwaves
should lead to precipitation in the afternoon to evening hours
from the Western Kenai Peninsula north through Anchorage and into
the Mat- Su Valleys. Precipitation type is tricky with this
system due to the influence of the strong ridge and resultant
inversion embedded over the area. Surface temperatures hovering
between upper 20s and low to mid-30s also make for a tricky
forecast. With this, and no meaningful cold air advection in sight
until Monday and Tuesday, freezing rain is likely to develop from
the Western Kenai Peninsula north through the Anchorage Bowl and
into the southern Mat-Su Valleys. Luckily, accumulation will only
range from a trace to less than one tenth inch across these areas.
There is a possibility of rain in these areas as well during peak
heating, but as we move into the overnight hours and temperatures
fall back below freezing, freezing rain may re-develop or wet
roadways will re-freeze. Please see the associated Winter Weather
Advisories for more details.

As we move into Monday and Tuesday temperatures aloft will slowly
cool down as cold air wraps in from the west. However, coastal
areas are likely to see rain continue through Tuesday with steady
onshore flow and warmer air near the surface. There is some
uncertainty in where a series of meso-lows will develop and move
through Tuesday, but rain and mountain snow will likely persist
through midweek, with slight chances for interior areas.

&&

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

An upper-level ridge continues breaking down over the northern
Mainland while a North Pacific low approaches from the west. The
low will reach the western tip of the Alaska Peninsula by Sunday
night and then continue east, exiting into the western Gulf by
Tuesday morning. Chances for rain along the Alaska Peninsula
increase early Sunday as a result of southerly flow along the
front of the low. Though showery in nature, increased chances for
precipitation spread north across the Southwest coast and
Mainland during the rest of the day on Sunday. Precipitation type
for the Bristol Bay area will likely be a wintry mix while inland
locations should see mostly snow. In general, precipitation
amounts for the next few days are expected to be relatively minimal.
An amplified, upper trough will reach the Alaska Peninsula tip on
Tuesday afternoon and then track east over Bristol Bay and
coastal Southwest by the end of Tuesday. Northerly small craft
winds will develop across the Southwest coast and Alaska Peninsula
while colder Arctic air is ushered into the domain. Precipitation
will become more widespread by Tuesday afternoon, and snow is
expected to become the main precipitation type as a result of the
colder airmass in place.

&&

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

A North Pacific low is spinning south of the Central Aleutians
and will track to the western tip of the Alaska Peninsula by
Sunday night. The low continues east and will exit into the
western Gulf by Tuesday morning. An upper-level trough currently
over eastern Russia will dig south into the western Bering by
Sunday night. The trough will amplify as it tracks to the eastern
Bering by Tuesday morning and then into Southwest by the end of
Tuesday. Deep northerly flow along the backside of the low and
with the upper trough will usher cold Arctic air across the Bering
and Aleutians through most of Tuesday. Northerly winds along the
western periphery of the low will be widespread gales with swaths
of storm-force possible over the central Bering on Sunday. The
colder air, strongest winds, and bulk of precipitation will
gradually move from the western Bering east as the system tracks
toward the Mainland for the next few days. The combination of
strong winds, colder air temperatures, and low sea surface
temperatures means that freezing spray is likely in the northern
Bering Sea for Monday and Tuesday. A transient upper ridge will
build in the wake of the trough and precede the next system of
interest. The warm front and cold front extending from a Kamchatka
low is advertised to enter the western Bering on Tuesday morning
and then Wednesday morning, respectively. General southerly flow
with this system will return warmer temperatures to the Bering and
Aleutians by the end of Tuesday.

&&

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

There is good agreement on a pattern change in the long term
forecast period, with a shift to colder weather likely the latter
half of this week as broad longwave ridging pushes east of the
state. On Wednesday, a decaying low in the northern Gulf of Alaska
in the vicinity of Prince William Sound will support upslope
showers along the coastal mountains through the evening hours.
Meanwhile, a strong shortwave trough stretching across western
Alaska helps to advect a cold air mass over Southwest Alaska
eastward, leading to colder temperatures and supporting the
eastward progression of a cold front into Southcentral Alaska. As
a result, Southcentral Alaska can expect snow showers inland from
the coast on Wednesday as the front pushes east and weakens. The
cold air mass also streams into the North Pacific across the
Aleutian Range. In combination with a strong low in the eastern
Gulf of Alaska, this promotes gusty winds to gale force out of
bays and passes on the south side of the Alaska Peninsula and
within the western Gulf of Alaska. The development of offshore
flow in response to low pressure in the Gulf also shuts off
precipitation along the north Gulf coastal mountains Wednesday
night.

The next impactful weather system for southern Alaska also exits
far eastern Russia into the northern Bering Sea on Wednesday. The
large low pushes eastward with a potentially storm-force front
moving through the Aleutian Islands. Wednesday night, the front,
weaker further north, reaches the Southwest coast. While there is
some uncertainty, this looks to bring mostly snow to the region
with a sufficiently cold air mass already in place. Beyond this
point, model guidance diverges significantly. GFS and GEM agree
that the bulk of the upper-level energy associated with the low
dive south across the eastern Bering Sea with the front decaying
quickly as it moves inland. The EC presents an alternate
solution, whereby the low remains consolidated much further north
in the Bering Strait and the front pushes eastward, surviving to
bring another round of snow to Southcentral by Friday. The
question will be how far west along the Aleutian Chain the cold,
northerly flow on the back side of the low will begin to surge
across. The further west solutions of the GFS/GEM bring gale force
northwesterly winds across the central/eastern Aleutians on
Thursday, while the more northerly track of the EC spares the
islands and initiates winds out of gaps in the Alaska Peninsula on
Friday. This will also impact where widespread showers will result
if cold air advects over the relatively warm waters of the
central/eastern Bering Sea, which would also affect parts of the
Aleutian Chain and the Pribilof Islands.

By Friday, there is good agreement that low pressure will be
present in the Gulf of Alaska, which will help to draw in and
reinforce colder air over southern mainland Alaska while enhancing
precipitation chances along the north Gulf coast. Gap winds also
shift south of the Alaska Peninsula and into the western Gulf as a
result. At the same time, the next system begins to track into
the far western Bering and pushes its front northward, bringing
warmer conditions and rain to the western/central Bering Sea and
Aleutians through Saturday.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...Winter Weather Advisory 101 111 121 145.
MARINE...Storm Warning 414.
		 Gale Warning 119 120 131 175-178 185 411 412.
FIRE WEATHER...NONE.

&&

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

SPECIAL WEATHER STATEMENT
National Weather Service ANCHORAGE AK
151 AM AKST Sun Nov 20 2022

AKZ161-210100-
Bristol Bay-
Including the cities of King Salmon, Dillingham, Naknek,
and Pilot Point
151 AM AKST Sun Nov 20 2022

...FREEZING RAIN POSSIBLE TODAY THROUGH TONIGHT...

Dillingham and inland areas up to Koliganek and New Stuyahok may
see freezing rain/drizzle today into tonight. Any ice
accumulations that occur are expected to be minimal with a
transition to periods of plain rain and wintry mix.