Gale Warning 255, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
523 AM AKST Thu Feb 29 2024

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 through 3/Today
through Saturday night)...

The big weather message for Southcentral, the Gulf, and Kodiak
Island is "cold and windy". A deep trough and accompanying Arctic
airmass are firmly entrenched over the region, with a building
ridge upstream over the Bering Sea. A compact vertically stacked
low in the eastern Gulf took an unexpected track, lifting north
and west toward Southcentral late yesterday through the overnight
hours. This low is centered in the northern Gulf this morning,
less than 100 miles to the southeast of Middleton Island. With two
other weaker upper level lows embedded in the trough circulation
to the south, expect this low to be pulled back southward by later
this morning. Still, it's closer proximity to Southcentral has
led to an overall stronger wind field across the Gulf waters and
further tightened up pressure gradients region-wide leading to
stronger gap winds. Some of the strongest observed winds, which
have been fairly steady overnight, include 70 mph at the exit of
the Copper River Delta, 65 mph through Thompson Pass, 60 mph in
Seward, and 60 mph for the Kodiak City area. Gusty winds are being
observed across nearly the entire forecast area. Temperatures
heave slowly but steadily fallen since yesterday afternoon, sitting
in the single digits to teens for most of the region. Wind chill
reading generally range from zero to 20 below zero, with colder
readings in the Copper River Basin and surrounding mountain
passes. All of the cold air and wind is also producing widespread
freezing spray across the Gulf coastal waters. Lastly, snowfall
with the Gulf low pushed onshore in the Cordova area last evening,
with some localized areas also spreading up into portions of the
Copper River Basin. Bands of snow are trying to push westward
toward the eastern Kenai Peninsula this morning, though dry
offshore flow is working against precipitation reaching the
ground. If snow does reach the ground, it will produce localized
areas of reduced visibility in blowing snow.

As we head through the remainder of the work week, the upper level
wave pattern will shift eastward. The trough and associated lows
in the Gulf will southeastward toward British Columbia and the
Northwest CONUS by Friday. A trailing short-wave trough will cross
Southcentral Thursday night through Friday, providing another
forcing mechanism for windy conditions while surface temperature
and thermal gradients remain steady state. This is particularly
favorable for the Valdez area, so have strengthened winds for this
time period in the latest forecast. An upper level ridge will
slowly build in from the west Saturday, moving overhead of
Southcentral saturday night. This will finally allow winds to
lighten up for much of Southcentral. As is always the case,
coastal gap winds will linger the longest. As winds diminish in
a dry airmass (with ridge aloft), radiational cooling will kick in
and lead to rapid temperatures drops Saturday night. Thus, have
shifted the coldest night of the week to Saturday night/Sunday
morning, at which point most of Southcentral will likely observe
sub-zero temperatures. The one wild-card for the temperature
forecast will be moisture approaching from the Bering Sea as the
ridge continues eastward. There is some uncertainty in the arrival
of initial cloud cover, which could limit temperature falls over
western portions of Southcentral with an arrival early Sunday. In
any case, it looks like the cold and windy pattern will come to an
end as we move into the new work week.

SEB

&&

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

Little overall has changed compared to yesterday in terms of the
synoptic pattern in place. Strong northwesterly flow continues
unabated across Southwest, particularly along and south of the
Alaska Peninsula. A frigid Arctic air mass continues to stream
southward into much of Southwest, with temperatures by and large
now dipping into the -0s to -10s. A strong upper ridge continues
to build over much of the Bering Sea to the west of the deep
troughing still in place over the southern Mainland. Across the
western half of the Bering Sea, a strong warm front is continuing
to make progress north and east, and this front will soon become a
wintry trouble maker as it collides with the cold air mass in
place across the rest of the outlook area.

By later this afternoon and evening, the aforementioned front
will approach the central Bering and Aleutians as it begins to
slow its eastward progress a bit. By this point, an unusual
combination of warm air aloft overrunning a cold air mass a few
thousand feet thick near the surface will begin to set the stage
for a wintry mix of sleet, snow and freezing rain along and ahead
of the front. Across the eastern Aleutians, precipitation should
start as mostly sleet and snow this evening, then begin to change
to freezing rain later tonight before going over to all rain as
surface temperatures warm above freezing. A similar transition is
likely to take place as precipitation spreads into the southern
Alaska Peninsula starting late Friday morning, but the transition
over to rain or a rain snow mix will likely take longer due to
initially colder temperatures in place and a further slowing of
the front's progression. While there is still uncertainty for
timing of precipitation type transition, areas around Cold Bay,
False Pass and Nelson Lagoon could see the wintry mix last all the
way to Saturday afternoon until temperatures aloft finally cool
below freezing. Farther north across the Pribilofs, gale force
winds will initially lead to areas of snow and blowing snow late
tonight, but a transition over to mostly sleet is likely as the
warm nose aloft moves in on Friday. See the Winter Weather
Advisories now in effect for all three of these regions for
further details.

Between Friday and Saturday, the front will continue to move
slowly east as it finally begins to approach the Southwest coast.
Temperatures over Southwest should finally begin to warm up into
the 0s to 10s above by Saturday as the Arctic air mass retreats.
Light snow chances will also return to Bristol Bay and the
Kuskokwim Delta by Saturday afternoon as the weakening Bering
front approaches the coast. Meanwhile, another low will cross the
Aleutians into the western Bering with another round of rain and
snow pushing across the western Aleutian Chain on Saturday.

-AS

&&

.LONG TERM FORECAST (Days 4 through 7) Sunday through Wednesday...

Forecast models show an active series of moderate amplitude upper
level troughs and ridges moving across the Bering through the
Alaskan Mainland. Model tracks and strengths continue to be more
uncertain through the forecast period. Interior Alaska is
dominated by an upper level ridge, flexing with the transient
shortwaves that have been moving through the pattern. However,
Arctic cold and dry conditions will continue to drain across the
Mainland through the period. Conditions over the Bering remain
under the influence of the broad upper low with surface fronts or
troughs rotating around the Bering through Wednesday. The most
active weather will be widespread precipitation, with snow over
the Northern portions and mixed rain and snow or rain and gusty
winds along the Aleutians. A well developed North Pacific low
spreads its influence across the Aleutians for Tuesday with mostly
rain and gusty winds with areas of gale force gusts moving into
the Alaska Peninsula and Kodiak Island by Wednesday.

Kutz

&&

.AVIATION...

PANC...VFR conditions and strong northerly winds will persist
through the TAF period. Gusts are expected to range from 25 to 30
knots.

&&