High Surf Advisory 2, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
515 AM AKDT Wed Aug 24 2022

.ANALYSIS AND UPPER LEVELS...

Longwave trough exists across Southern Alaska, extending in the
Gulf of Alaska. A low pressure system sits just south of Kodiak
Island and rotate in the general area into tomorrow, fizzling out
by Thursday afternoon. A shortwave protrudes westward from the
trough and extends out over the Central Aleutians, with a surface
low embedded within it, and will spend the rest of the day pushing
into the North Pacific. A series of other, weaker, shortwaves
pass over Southcentral Alaska are resulting in periodic rain
showers this morning. High pressure ridging will continue over
the Bering through the morning hours today before being flattened
out by an approaching front. Areas of low hanging clouds and some
patchy fog are notable under the ridge as well. The front entering
the western Bering this morning hangs off a low over eastern
Russia. The front will track across the Bering towards the
Southwest coast through Thursday evening, pushing onshore Thursday
night, but the low itself will remain mostly over Russia before
moving into the Gulf of Anadyr and over Saint Lawrence Island
Friday morning.

&&

.MODEL DISCUSSION...

There are a few embedded surface lows within the trough pattern
that the models are still struggling with, but overall, models
remain in relatively good agreement through the short term. There
is a good handle on the large low over eastern Russia, as well as
with its associated front as it moves across the Bering over the
next couple of days.

&&

.AVIATION...

PANC...A couple of shortwaves passing over will result in periods
of light rain showers and ceilings dropping below 5000 feet
Thursday morning. Conditions should, however, stay mostly VFR.

&&

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

The satellite imagery does not look all that different from last
night over Southcentral with the upper level low spinning near
Kodiak and the front running due northward into the Prince
William Sound area from well south of 40N. However, there are some
important differences with the location of the upper level low
and that low is taking the more westerly track as discussed
yesterday. That has brought rain over Anchorage and the Matanuska
Valley overnight, but to the west side of Cook Inlet as well.
This will translate to a wetter day for these areas as that pesky
low just takes it time heading northeastward. It should make the
AlCan border Thursday afternoon which will allow weak ridging
over Southcentral behind it. As has been the case this month, the
break will be short-lived as the next soggy system moves into
Southcentral from the west on Thursday night and lingers through
Friday.

Expected rainfall amounts with this next system look to
be around .5 (half-inch) for the western Kenai Peninsula through
Anchorage. The Matanuska valley should be closer to .75 inch with
increasing rainfall amounts northward with up to 1.5 inches in
the central to northern Susitna valley. The overall wettest area
will again be around Prince William Sound where there should be
another 1.5 inches to go on top on the 1 inch expected today.

As to the question as to whether there will be a nice clearing
trend this weekend behind this next system: (Spoiler Alert) the
answer is no. The upper level trough will remain over the region
making it a rinse and repeat situation with the emphasis on the
'rinse' part.

&&

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

Relatively quiet weather across Southwest Alaska this morning.
With enough clearing overhead, a few locations have gotten some
fog and may potentially last through a good portion of the
morning. The large low south of the Alaska Peninsula is beginning
to shift towards Kodiak Island. Showers are spilling over the
Alaska and Aleutian mountain range but drying up before reaching
Iliamna, King Salmon, or Pilot Point. Quieter weather will come to
end tonight though.

A front is expected to move across the Bering Sea during the day
today. A large upper level jet will help to press plenty of
precipitation and strong winds to the Kuskokwim Bay and coastline.
Winds will increase to gale force near the coastline early
Thursday, impacting coastal communities from Kipnuk to Quinhagak.
High surf also expected for this area. Strong southerly winds
could funnel through the Kuskokwim River to Bethel. Areas south of
the Kuskokwim, such as Cape Newenham and Togiak, can also expect
strong winds through Thursday afternoon, though impacts should be
less. Winds will gradually decrease Thursday night, but breezy,
onshore flow and rainy weather is expected to continue through
Friday.

&&

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

The high pressure ridge over the western Bering this morning will
move along the Aleutians today and be replaced with the next
trough. A large upper level jet will stretch across the Bering Sea
today, helping to increase winds from west to east throughout the
day. Winds will noticeably increase for the Pribilofs and St
Matthew Island this evening and peak tonight. Precipitation is
expected with this north-south frontal passage and should span the
entire Bering to the Aleutians. By Thursday morning, the swath of
precipitation and winds will be over the eastern Bering and
Central to Eastern Aleutians. It will not be until late Thursday
morning, that winds peak and span the entire eastern Bering from
the Eastern Aleutians to the Southwest coast. Winds could become
gale force from Cape Newenham northward to Nunivak Island with
higher gusts. Windy and rainy conditions may linger behind the
frontal passage through Friday afternoon with the higher chances
for precipitation across the Aleutians and the higher winds
towards the western Bering on Friday.

&&

.MARINE (Days 3 through 5: Friday through Sunday)...

Gulf of Alaska: Forecast confidence remains moderate due to
model differences between the placement and intensity of synoptic
scale features. However, confidence is high winds are expected to
remain below gale force with no high seas expected.

Aleutians/Bering: Forecast confidence is low due to significant
model differences in the pressure fields across the eastern
Bering/Aleutians. Confidence is high that winds will remain below
gale force across the central and western Bering. However, there
is a chance for gale force northwesterly gap winds along the
eastern Aleutians and western Alaska Peninsula on Sunday.

&&

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

Forecast confidence is above average with respect to the overall
synoptic pattern during the extended period. Low pressure is
expected to move southeastward from the Bering Strait into the
Gulf of Alaska and will result in more clouds than sun as well as
a higher probability of precipitation across Southcentral and
Southwest Alaska. Confidence remains low with respect to precipitation
amounts due to significant model differences in the precipitation
field as well as uncertainty to how strong the downsloping force
will be on the leeward side of the Chugach Mountains.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...Flood Advisory 121
MARINE...Gale 180
FIRE WEATHER...NONE.

&&

SYNOPSIS AND MODEL DISCUSSION...KM
SOUTHCENTRAL ALASKA...EZ
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...VR
MARINE/LONG TERM...ED

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