NWS Anchorage, AK wrote its last area forecast discussion before the first event at Jan 21, 6:15 PM AKST, 10 hours 27 minutes earlier.
Area forecast discussion, Jan 21, 6:15 PM AKST, 10 hours 27 minutes before
Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
615 PM AKST Tue Jan 21 2025
.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 through 3: This
afternoon through Friday afternoon)...
Active weather persists across Southcentral Alaska. A strong
front transits across the north Gulf coast through early tomorrow
morning, bringing gusty winds and moderate rain/snow. Several
weaker storms follow behind this front from Wednesday through
Thursday, leading to unsettled weather but nothing particularly
hazardous... though we're keeping an eye on snow amounts for the
Homer Bluffs and Susitna Valley. By late Friday morning, a warm
and wet atmospheric river begins to move in, hinting at much more
impactful weather this weekend. For the front moving through
tonight, we are currently monitoring heavy snow in Turnagain Pass,
with snowfall rates of 1-2 inches per hour potentially leading to
lower visibilities through 9 PM. Please see the Winter Weather
Advisory for more information.
Diving into the details...strong winds and light to moderate
precipitation are the name of the game as a front lifts northwards
across the Gulf coast. The strongest gusts/peak winds so far have
been: 71 mph at Portage Lake, 68 mph at Whittier Access Road, 59
mph at Middleton Island, and 55 mph at both Cordova and Kodiak
Airport. Most of the precipitation has fallen along Eastern Kenai
Peninsula and the Kachemak Bay area, though Anchorage did pick up
a trace of snow/graupel earlier today. The front will gradually
weaken as it runs up against the coast, with winds diminishing by
late tonight.
Behind the front, south to southwesterly flow will usher in
cooler air. Weaker upper level shortwave troughs moving in behind
the front will help prolong precipitation along the coast, as well
as bring light precipitation to areas bordering Cook Inlet.
Expect a light band of rain/snow mix to move north across Western
Kenai Peninsula, Anchorage, and Mat-Su from late Wednesday morning
through Wednesday evening. Any precipitation that falls should be
light. There is some question of whether the air will be cold
enough to support all snow for these locations; have kept the
forecast precipitation type as rain/snow mix for now as the
coldest air looks to move in after this band of precipitation has
gone through. By Thursday morning, a chance for all but the Copper
River Basin and Kodiak Island to see another round of light snow
as a quick-moving shortwave transits west-to-east across
Southcentral.
We'll be monitoring two areas with the Wednesday and Thursday
storms: the Homer Bluffs and northern Susitna Valley.
Southwesterly flow is favorable for higher snow amounts at these
locations due to enhancement from upslope flow along the terrain.
Susitna Valley could pick up a fair amount of snow in the coming
days as several rounds of precipitation move through. Ballpark
values are around a foot or more north of Talkeetna, though this
will be occurring over a long duration of light to moderate
snowfall rates. For the Homer Bluffs, models tend to underdo snow
amounts, especially in convective snow showers like the type we'll
see on Wednesday. Snow amounts look higher for the Bluffs
Thursday, but we're expecting temperatures to warm up ahead of
Friday's atmospheric river, which could cut down overall snow
amounts. All told, confidence is low regarding the potential for
snow or blowing snow on the Bluffs, so that will bear watching.
-Chen
&&
.SHORT TERM FORECAST SOUTHWEST ALASKA AND THE BERING
SEA/ALEUTIANS (Today through Friday afternoon)...
Currently, spotty showers are affecting the southwest mainland
due to the presence of a low over Bristol Bay. These showers are
mostly in the form of rain due to a warmer air mass in place
driven by southerly flow. The low will weaken as it moves onshore
later today and will break down into a trough as it moves
northeastward. On the backend of the weakening low, winds will
shift to a more westerly direction, allowing cold air from the
Bering to intrude and convert any lingering precipitation to snow
early Wednesday. This will be shortlived, however, as a weak ridge
pushes in from the west by Wednesday afternoon, diminishing
precipitation chances. Looking at the Bering, a Kamchatka low
swings in, bringing rainfall and high-end gale force winds to the
western Aleutians this afternoon. Cooler air behind the low will
allow for snow showers in the same area. This low will quickly
track eastward, bringing a burst of precipitation and gale force
winds to the Bering and Aleutians throughout Wednesday.
Following the previous low is a more compact North Pacific low
riding an atmospheric river. This low will push the prior low
onshore more quickly, allowing for some brief inland snow showers,
then rain showers as southerly flow drives a warmer airmass
inland by Thursday morning. Gale force winds will also affect
Bristol Bay and the Kuskokwim coast. The North Pacific low
mentioned before will rapidly move northwards into the Bering,
passing by the Pribilof Islands by Thursday afternoon. Heavy
precipitation mostly in the form of rain will accompany this low.
The more impactful feature, however, will be the winds. This low
will drive winds to storm force category, which will affect the
Eastern Aleutians and Alaska Peninsula from Nikolski to Cold Bay,
as well as the Pribilof Islands and Kuskokwim coast. The effects
on the Kuskokwim coast are notable because surge from this low
will drive waves up and could cause coastal flooding. Communities
such as Kwigillingok and Kongiganak could be affected. Due to this
threat, a Coastal Flood Watch has been issued for the Kuskokwim
Delta Coast. Water levels could rise 4 to 6 ft above the normal
highest tide line from Wednesday evening to Friday morning. As the
low tracks northward, winds will quickly diminish by Friday
afternoon. However, the atmospheric river will remain, and will
drive tons of moisture into the southwest mainland. This means
that moderate to heavy precipitation will affect a large swath of
the southwest mainland including Bethel, Dillingham, King Salmon,
and Iliamna through the end of the short term.
It doesn't end there as a very cold air mass moves in from the
west. Temperatures will decrease in the Bering through Friday and
convective snow showers will affect the western and central
Aleutians, eventually reaching the Pribilofs by Friday afternoon.
The cold air will reach the Kuskokwim Delta region by this time as
well, transitioning rain into snow near Bethel. Looking a bit
ahead reveals that this cold air mass could drop temperatures
below zero in the mainland, especially in the northern regions.
Other implications are likely, so we will monitor as this event as
it draws closer.
-JAR
&&
.LONG TERM FORECAST (Days 4 through 7: Saturday through
Tuesday)...
Little change from previous discussion.
Strong winds, precipitation and unseasonably warm temperatures
will continue through Monday over much of Southern Alaska as a
frontal system moves across the region. A major change in the
weather pattern late Monday and into Tuesday will see Southerly
winds give way to a more northerly component across much of
Southern Alaska as an Arctic airmass dips southward into the lower
half of the state. Much lower temperatures are expected across
much of Southern Alaska by Tuesday.
A very strong longwave ridge along the U.S. and Canadian west
coast, coupled with a deep longwave trough with associated closed
low and frontal systems is expected to be moving up into the
northern Bering Sea and up into far northeastern Russia. Strong
pressure and temperature gradients between these two systems will
be very impressive even by Alaskan standards. The strong pressure
gradient setting up along this boundary, plus at least two
distinct stronger areas of low pressure that will move north along
it, will support strong southwest winds, initially over the
eastern Aleutians and Southwest. Stronger winds could also affect
parts of Southcentral on Sunday as the second low moves up from
the Pacific into Southwest. Heavy precipitation along the main
frontal zone is expected as deep moisture will help support rather
intense precipitation rates for much of Southwest and later
Southcentral compared to what is typically possible for late
January. Temperatures in many areas of Southwest close to sea
level will likely initially be warm enough for rain at lower
elevations, and this will likely also be the case as the front
shifts into Southcentral between Sunday and Monday. There could be
a transition over to snow across both Southwest and Southcentral
as cooler air begins to move in behind the front between Sunday
and Monday.
&&
.AVIATION...
PANC... The likelihood of wind shear from this morning through
late this evening remains. As a front moves through the Gulf
today, northerly winds change to a more northeasterly/easterly
direction mid-afternoon. Winds continue to shift southeast as
Turnagain Arm winds bend into Anchorage. Wind gusts will range
from 20 to 30 knots later this evening into Thursday. Otherwise,
VFR conditions expected.
&&