Gale Warning 457, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
533 AM AKDT Fri Aug 4 2023

.ANALYSIS AND UPPER LEVELS...

Overall the pattern remains fairly steady state to that over the
past few days. The high over the southern Mainland has shifted
more to the east, which has resulted in a more stable and maritime
airmass to move up Cook Inlet and into the southern Mat-Su. As
such, stratus is more prevalent today on the western side of the
Chugach and Kenai Mountains. Otherwise, conditions over
Southcentral are similar to those observed the past three days,
with convection initiating this afternoon over the terrain
surrounding the Copper River Valley and Marine Stratus over most
of the Gulf. Out west, interior areas were under a similar stable
and marine airmass from the high to the east, resulting in stratus
which has since mostly burned off underneath the August sun. Over
the Bering and far eastern Russia, two large low pressure systems
are beginning the merging process that will take place over the
coming days. As such, the region remains under a thick blanket of
low clouds with a couple areas of rain showers.

&&

.MODEL DISCUSSION...

Models continue to be in good short-term agreement with positions
and tracks of the Gulf and Bering lows, and stout ridging over the
interior. Confidence is high that a low just east of Russia and the
Bering low will merge tonight with the new low deepening over the
central Bering tomorrow with frontal boundary progressing across the
Bering towards the southwest coastline. Minor timing differences
still exist for the frontal boundary reaching the coastline.
Confidence starts to decrease towards the latter half of the weekend
as models struggle with the weakening Gulf low that will lift north
along the periphery of the ridge, and the evolution of the Bering
low heading into early next week.

&&

.AVIATION...

PANC...VFR visibilities and light winds to persist through the
TAF period. Some periods of MVFR ceilings are possible, mainly
this morning.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 through 3: Friday
through Sunday)...
The weather challenges for today are the same ones from the past
few days around Southcentral. Those questions revolve around the
thunderstorm coverage in the Copper River Basin and the amount of
stratus and across the rest of Southcentral. These stratus areas
generally range from 1500 to 3500 feet elevation across
Southcentral this morning. These clouds should diminish some and
lift a little with the daytime heating, but these clouds will not
be in a hurry to fully dissipate and fully clear out today.
Saturday has a better chance for some sunny breaks across the
region.

Once again the Copper River Basin is the only place that has any
appreciable instability today and a few thunderstorms are expected
to develop again there this afternoon into the early evening. It
does look like the atmosphere does begin to become a little more
stable by late evening and then the area of greatest instability
on Saturday will be mainly in just the northeast portion of the
Basin. This is due to a shift in the pattern beginning to take
place that will break down the ridging that has been over
Southcentral and will bring in southeasterly flow aloft on
Sunday. This will bring in rain to coastal areas with most of the
interior locations seeing little precipitation due to being on the
lee side of the mountains.

&&

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

An upper low moving east from Kamchatka merges with a weakening
low drifting west from St Matthew Island. This interaction will
support a surface low over the Bering that could deepen to as low
as 973 mb on Saturday morning. A powerful gale force front
associated with this low will form between the central Aleutians
and the Pribilofs on Friday, then shift towards the Alaska
Peninsula and Southwest coast by Saturday morning. Southerly wind
gusts as high as 50 to 60 mph will be possible where flow is
channeled through gaps across the southern Alaska Peninsula on
Friday evening, with similar gusts possible across the Kuskokwim
Delta and Bristol Bay near the coast on Saturday. Winds will
generally run parallel to the coastline ahead of the front, but
strong onshore flow into the northern side of the Kuskokwim Delta
will still lead to the threat for a minor storm surge near high
tide on Saturday. Please continue to monitor the forecast closely
for additional updates and details on the threat for higher than
normal water levels in this vicinity for Saturday.

Saturday night into Sunday, the front will weaken below gale
force as stalls along the Southwest coastline. Areas of light
rain will continue where aided by upslope flow into the
Alaska/Aleutian Range and Kilbucks, while scattered showers drift
around the weakening low across the Bering and Aleutian Chain.
Remnants from this storm will gather south of the Alaska Peninsula
late Sunday and quickly move towards the Gulf.

&&

.LONG TERM FORECAST (Days 4 though 7: Monday through Thursday)...

The long-term forecast focuses on the a large low over the Bering
Sea that looks to retrograde off to the northwest early next week
with a secondary low getting pinched off over the AKPen before
drifting towards the northern Gulf. While models differ
significantly  on exact placement of these features, overall
consensus has the Gulf low stalling as ridge over BC and the Yukon
prevents much further movement eastwards. The EC has this low
lifting towards the Southcentral coast with the GFS keeping the
center of the low much further to the south. The system over the
Bering Sea becomes convoluted by midweek with the EC and GFS in
similar agreement with low center dipping back towards the central
Aleutians. The Canadian remains the outlier here with the low
becoming more elongated as it moves over the Eastern Aleutians and
southern AKPen.

&&

SYNOPSIS AND MODEL DISCUSSION...BL
SOUTHCENTRAL ALASKA...EZ
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...ER
LONG TERM...MK