Gale Warning 744, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
443 PM AKDT Sun Oct 27 2024

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA
(Today through Tuesday evening)...

48 HOUR FOCUS:

* Widespread snow for much of Southcentral arrives tonight and
  continues through Tuesday evening impacting the daily commutes.

* The heaviest snow is likely early Tuesday morning through late
  Tuesday morning.

* Winter storm watches for western Kenai Peninsula and the
  Anchorage areas have been issued in addition to a winter weather
  advisory for the Matanuska Valley.

A deep trough currently in Southwest Alaska and a low currently
in the North Pacific south of the Alaska Peninsula will bring a
mix of rain and snow to Southcentral Alaska over the next 48
hours. Through Tuesday, the low will progress along the eastern
coast of Kodiak Island and the Kenai Peninsula toward Prince
William Sound. Concurrently, the trough moves almost due eastward
across Southcentral Alaska. These two features' interaction will
result in a combination of rain, rain/snow and snow to
Southcentral.

Digging deeper, continued southwesterly winds bringing warmer air
to Kodiak Island and southern Kenai Peninsula will keep
precipitation as rain for most of the event. Colder air arriving
late Tuesday morning changing the rain to a rain/snow mix and then
light snow with accumulations ranging from a trace in Kodiak City
to two inches in Homer. Farther northward on the Kenai Peninsula,
cooler air will arrive faster resulting in a longer snowfall
period. Therefore, snowfall accumulations varying from 6 to 12
inches on the western side to 3 to 6 inches on the eastern side.

The aforementioned southwesterly flow into Turnagain Arm,
Anchorage and Whittier will result in varied snowfall
accumulations. The greatest chance of a rain/snow mix exists on
the eastern coast of the Kenai Peninsula and Turnagain Arm. With
a strong easterly wind, a longer period of rain/snow showers is
expected to bring snow accumulations closer to the trace to 3
inches range in these areas at sea level. A change over to all
snow is expected in Anchorage and the Mat- Su Valley resulting in
6 to 12 inches of snow accumulating in these locations by Tuesday
evening. High confidence for a period of intense snowfall is
expected over the Kenai Peninsula northward to the Mat-Su Valley
early Tuesday morning through late Tuesday morning. Though
confidence is low regarding the band's exact location, where it
sets up would cause brief periods of localized higher snowfall
amounts and poor visibility.

As the low exits Southcentral Alaska, it deepens to 977 mb in the
northern Gulf of Alaska bringing interior snow, coastal rain and
gale to storm force winds in the Northern Gulf of Alaska and
Prince William Sound as well as gap winds in the usual locations
Tuesday night/Wednesday.

-DJ

.SHORT TERM FORECAST SOUTHWEST ALASKA AND THE BERING
SEA/ALEUTIANS (This afternoon through Wednesday evening)...

* Winter Weather Advisory in effect from 7 PM this evening until 6
  AM Monday for interior Bristol Bay from Dillingham north,
  including Koliganek and New Stuyahok.

* Special Weather Statement for moderate snow across the Lower
  Kuskokwim Valley tonight through Monday morning.

The well advertised frontal system is currently coming ashore of
the Kuskokwim Delta and northern Bristol Bay coasts this
afternoon. Snow and mixed precipitation have been observed across
Nunivak Island and Kipnuk this afternoon. The front will continue
pushing inland overnight tonight through Monday. Precipitation
will begin as snow this evening across Bristol Bay before a
transition to freezing rain overnight tonight into early Monday
morning. The freezing rain threat is primarily for interior
locations from Dillingham northward, including Koliganek and New
Stuyahok. Thus, the Winter Weather Advisory continues to remain in
effect for those locations due to the freezing rain threat.
Freezing rain should then transition to rain Monday morning;
although there continues to be some uncertainty in exactly when
the transition will occur. If cold air hangs on longer, expect a
few hundredths of an inch of ice accumulation. If cold air erodes
quicker, expect mainly a glaze.

Meanwhile, the Kuskokwim Delta can expect light snow through this
evening, especially across interior locations where cold air hangs
on longer. Accumulations will be light and in the 1 to 3 inch
range. Further inland, locations like Aniak could also see a brief
period of freezing rain or mixed precipitation as warmer air aloft
looks to sneak in tonight. Cold air aloft works back in late
tonight into early Monday morning and changes precipitation back
to snow. Generally expect 3 to 6 inches of snow across the Lower
Kuskokwim Valley, especially from Crooked Creek southeastward to
Lime Village. Totals could be a little bit higher than that
towards the Western Alaska Range.

The front continues moving eastward to Southcentral Alaska through
Monday. Cold air begins to filter back in as a ridge across the
central Bering Sea looks to amplify. Strong cold air advection
along with upper-level energy will help to drive gusty gap winds
through the bays and passes of the southern Alaska Peninsula
starting Monday night and persisting through Tuesday evening.

Attention then turns to the next weather-maker which will take
form of a storm-force low Monday evening. The storm-force front
will impact the western Aleutians and western Bering late Monday
night into Tuesday morning. Hurricane-force gusts are possible
with this system. The front will weaken to gale-force as it
reaches the central Aleutians Tuesday. However, as the storm
enters the far western Bering, southwesterly storm-force winds
are likely in the western Bering and western Aleutians on the
southern flank of the storm Tuesday night into Wednesday. The
initial front, remaining gale-force, will make it to coastal
Southwest by Wednesday afternoon. Confidence in precipitation-type
is currently low. Generally expected a rain/snow mix to start
before going over to rain at the coast, with more in the way of
snow inland where cold air hangs on longer.

&&
.LONG TERM FORECAST (Days 4 through 7: Thursday through Sunday)...

The Alaska Weather map continues to display an energetic weather
pattern through the forecast period. Model confidence remains
good, although some strengths and tracks need adjustments to
maintain the overall clustering. Most of the active weather occurs
across the Southern portions of the state through the weekend. A
broad upper level low over the Bering serves as the conduit for a
series of strong surface low and fronts passing West to East. The
first feature is a frontal wave across the Alaska Peninsula and
over Kodiak Island Thursday that pushes across the Gulf of Alaska
by Friday. Locally heavy rains and gusty winds less than gale
force spread along the North Gulf Coast with this system.

Out West, a second well developed low moving over the Central
Bering with central pressures briefly below 960 mb through Friday
before weakening. Heavy rains spread over the Aleutians and Bering
into the Alaska Peninsula. Moving into the region from the North
Pacific, a second stronger low with central pressures in the 950s
brings locally heavy rains high-end gales with storm force gusts
up to the Aleutians Friday, spreading with the low over the AKPEN,
Southwest Alaska and Kodiak Island Saturday. Areas of heavy rains
continue to spread along the North Gulf Coast through Sunday.
Highest winds are expected to remain on the Pacific side of the
AKPEN, around Kodiak Island and diminishing as they move across
the Gulf by Sunday.

&&

.AVIATION...

PANC...VFR conditions and light winds will persist at the
terminal through 12Z tomorrow morning. Conditions will then
rapidly deteriorate after 15Z as light snow arrives. With deep
southwest flow, ceilings will drop with the arrival of the snow
but is expected to remain at mainly MVFR levels through the day
Monday, before IFR ceilings and visibilities with heavier snow
begin Monday evening.

&&