Gale Warning 330, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
449 AM AKDT Thu Apr 20 2023

.ANALYSIS AND UPPER LEVELS...

An amplified pattern remains over the region as a cold upper-
level trough is situated over the Mainland and an upper-level
ridge builds over the Bering. Looking at Satellite Imagery, clear
skies and generally calm conditions persist over the mainland with
the exception of a few higher- level clouds over Southcentral. A
frontal boundary associated with a Kamchatka low remains nearly
stationary over the western Aleutians, keeping southerly flow and
rain over the western Bering and Aleutians.

&&

.MODEL DISCUSSION...

Models are in generally good agreement through the short term.
By Friday, there is disagreement about the location of an upper-
level low tracking from the North Pacific into the Gulf.
Furthermore, by the weekend, an upper-level trough over the
northern Arctic will eventually drop southward, eventually
interacting with the aforementioned Gulf low; however there is
still low confidence regarding timing, location, and exact track.

&&

.AVIATION...

PANC...VFR conditions and light winds will persist.

&&

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

Other than passing high clouds over Southcentral from easterly
waves wrapping around a low over the eastern Gulf, generally quiet
weather is expected for the next couple days. High temperatures
in the mid 40s to low 50s is possible for many locations with lows
near or below freezing. Light, northerly winds could accompany
the coastal gap locations as well.

Toward the weekend, a trough over northeastern mainland will
protrude southward into Southcentral beginning Saturday that could
allow cooler air to filter south with precipitation spreading
from north to south. The precipitation type will be a forecast
challenge as warmer air during the day could lead to an initial
onset of rainfall or rain and snow mix. Then as temperatures cool
with the transitioning airmass and its coinciding nighttime lows,
the precipitation type could be snow. Timing of the trough will be
a big factor in the outcome. Accumulations would be light.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 through 3: Today
through Saturday night)...

Relatively pleasant, quiet spring conditions are set to continue
through the start of the upcoming weekend as a blocking upper
ridge centered over the northern Bering continues to impart
steady, dry and offshore flow across all of Southwest with mostly
clear skies expected to persist through at least Friday night.
Temperatures should continue to push well above freezing during
the day for the next couple days as well, with most spots expected
to see upper 30s to mid 40s for afternoon highs both today and
Friday. By Saturday, an upper level trough originating from the
Arctic will drive south-southwest mostly into Southcentral. This
should result in strengthening northerly flow across Southwest
with some increase in cloud cover, and this should advect in a
noticeably cooler air mass as well. Still, Saturday highs should
manage to get into the mid to upper 30s thanks to our long hours
of daytime heating and only a modestly cooler air mass moving into
place.

&&

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

Most of the region will see quite benign conditions over the next
few days as a blocking high remains stationed across most of the
central and northern Bering Sea. A decaying front west of Adak
will continue to focus areas of very light rain and small craft
level winds across western parts of the Aleutian Chain, although
even this feature will shear apart by this evening. A corridor of
easterly small craft to low end gales will also develop near a low
drifting across the North Pacific along and south of the Alaska
Peninsula and eastern Aleutians, eventually diminishing as the low
pulls south on Friday night. A stronger front will approach the
western Aleutians from Friday night into Saturday, with southeast
winds potentially picking up to storm force sustained ahead of the
boundary where a tight pressure gradient will set up between the
strong Bering ridge and the front's parent low near Kamchatka.
Moderate rainfall perhaps totaling up to 1 inch will be possible
with this front as it passes across the far western Aleutians
through Saturday evening along with around 60 mph wind gusts for
areas near Shemya.

&&

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

The long-term forecast begins on Sunday with upper-level troughs
and embedded lows located over Southcentral and west of the
western Aleutians near the Kamchatka Peninsula. A ridge of high
pressure is wedged in between the troughs over the Bering Sea and
Aleutians. The main talking point for the long term forecast is
the expected return to below normal temperatures for the Mainland.
As the aforementioned trough and low over Southcentral continue
to drop south from the Arctic on Sunday and Monday, it will allow
a cold airmass to settle into much of the Mainland. The coldest
850 mb temperatures are expected across Southwest and north of
the Alaska Range, however Southcentral should still see colder
temperatures as some of the Arctic air filters through the Alaska
Range. Low pressure on either side of the ridge will gradually
pinch off the high pressure to the north, and by Monday morning,
a longwave upper trough with multiple embedded lows will stretch
from the Bering east across southern Alaska and into Southeast.
By midweek, temperatures begin to moderate as southerly flow
increases across the southern Mainland and the Arctic airmass
retreats northward.

&&

 $$

SYNOPSIS AND MODEL DISCUSSION...NSC
SOUTHCENTRAL ALASKA...VR
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...AS
LONG TERM...AF