Gale Warning 410, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
439 AM AKDT Wed Jul 6 2022

.ANALYSIS AND UPPER LEVELS...

Barometric pressure is steadily falling across Southwest Alaska
as the broad upper level low that was stalled over the western
Bering is beginning to move east. A large band of cloud cover is
moving over the Kuskokwim Delta and Bristol Bay and although radar
is showing precipitation within this swath, only a few surface
observations are reporting rain around midnight. Dense fog
continues to lower visibility in the Pribilofs. Zonal flow with an
upper level jet streak and plenty of cloud cover stretches along
the Aleutians.

Contrasting the west, mostly clear skies with a few clouds under
southerly flow continues over Southcentral. An upper ridge remains
over the Alaska interior and east where a few thunderstorms have
diminished over the Alaska Range and the Wrangell Mountains just
before midnight. Low stratus and fog along the Gulf coast is
observed on satellite and beginning to filter further inland
through the valleys.

&&

.MODEL DISCUSSION...

Good, overall synoptic agreement continues in the short term and
confidence remains moderately high that a pattern shift is in
store for Southcentral Alaska towards the last half of the week.
Models diverge on where the strength and location of low center as
it reaches the Kuskokwim coast late tonight into Thursday and
continues through its progression over Bristol Bay. Models begin
to slowly realign again, primarily with its location as the low
reforms near Kodiak Island by Friday morning. The strength of this
low remains a bit less certain with the ECMWF systematically
producing a weaker low compared to NAM and GFS. As the forecast
moves into the mid to long range this weekend, brief model
consensus begins to diverge.

&&

.AVIATION...

PANC...VFR conditions and light winds will persist through at
least Wednesday evening. Turnagain Arm winds may possibly bend
gusty, southerly winds into the terminal area Wednesday night
through Thursday morning.

&&

.FIRE WEATHER...

Southcentral: A Red Flag Warning is in effect from this afternoon
through Thursday afternoon for Hot Dry and Windy conditions in
the Copper River Basin. Temperatures will once again see
widespread 80 degree readings this afternoon with RH values in the
lower to mid 20s. The winds will increase late this afternoon,
especially along the Copper River. The winds will subside after
midnight, but increase again Thursday morning and will probably be
stronger than today. However, there should be noticeably lower
temperatures on Thursday (though still in the lower to mid 70s)
and higher RH values as these southerly winds will finally tap
into moisture from the Gulf of Alaska to advect into the Copper
River Basin.

Southwest: A large Bering low moves eastward towards the
Kuskokwim Delta, then towards Bristol Bay for the last half of
this week. Fire weather concerns are low as a cloudier, cooler,
and wetter pattern will prevail. Although there is some
uncertainty in the timing and track of the low once it reaches
near Nunivak Island, the chances for wetting rains are expected
from west to east over the next few days. Gusty southeasterly
winds will also begin to increase through Kachemak gap into the
interior Bristol Bay during the later portions of each day. The
potential gusts may gradually increase with each successive
evening and also shift from southeasterly to more easterly
Thursday evening and Friday evening as the low moves south and
reforms near Kodiak Island. Precipitation chances continue through
Friday as scattered showers develop on the backside of the low.

&&

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

A front is moving into the Kodiak area today and that will herald
a change in the pattern for Southcentral. This front will push
farther inland than the previous one and bring more widespread
cloud cover to the area. However, it will also track into the Gulf
and not into Southcentral which will limit the rainfall to mostly
coastal areas with little making it over the mountains. This will
also increase the pressure gradient along the north Gulf coast
bringing in the Turnagain Arm winds, Knik River winds, and Copper
River winds the next few days. The southerly push of moisture
along the coast will also make it slow for the stratus that has
developed to lift or dissipate. Valdez and Whittier may see some
lifting of the clouds later today, but Cordova and Seward will
likely mainly see stratus persist into tomorrow.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 and 2)...

Early this morning the King Salmon and the Nome radars have a band
of precipitation moving into western Alaska. The Bethel radar is
down but based on satellite imagery, rain is also moving into
portions of the Kuskokwim Delta. There are surface lows near St
Matthew Island and south of Attu this morning. The position of the
longwave trough will favor a cool and wet pattern this forecast
period. The models are hinting at the development of a triple
point low near Kodiak on Thursday which would mean "wrap around
moisture" for the AKPEN and Western Alaska Range.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 and 2)...

This morning there is a jet core of 130 knots near Adak and there
is a second jet core near Kamchatka. An active pattern continues
for the Bering Sea and Aleutians as the longwave trough lingers
over the Bering Sea. There is a mature low near St Matthew and
another mature low south of Attu. The surface low near St Matthew
will move inland and a new low will form along the frontal
boundary near Kodiak on Thursday. Meanwhile the surface low near
Shemya will move closer to the western Aleutians today and then
become quasi-stationary. The GFS model continues to hold on to
negative height anomalies at 500 mb over the Central Bering and
Bristol Bay.

&&

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

Expect winds less than 35 kts and seas less than 20 ft for the
Day 3 through 5 period.

&&

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

Looking ahead into the extended forecast, the latest operational
model runs are in good agreement with the evolution and
progression of the synoptic scale features, but diverge in the
specific details towards the end of the period. An active weather
pattern change remains on track as an upper ridge from western
Canada to the eastern mainland Alaska slowly weakens as a longwave
trough and closed upper low moves into the eastern Bering Sea. As
we head into next weekend, the trough axis extends from the
Alaska Peninsula through the Gulf. Model guidance has been overall
consistent for this northwest to southeast orientation to bring
increased moisture and appreciable rain for the southern mainland.

At the surface, a frontal boundary extending from a low pressure
system near Kodiak Island progresses northward into Southcentral.
Much of the coastal areas and portions of interior Alaska can
expect widespread wetting rain along with some moderate to locally
terrain enhancing precipitation as increasing southerly flow
draws deep Gulf moisture. Significant rain is also likely for the
Gulf coasts, including Prince William Sound and along the eastern
Kenai Peninsula. With the Kenai River currently running high due
to warmer temperatures and snow melt, any coastal rain could push
the river into flood stage. Temperatures are also expected to
trend back toward normal as lower heights and thicknesses brings
in a cooler air mass spreading eastward across the state. By early
next week, a North Pacific low circulated around the trough may
spread additional periods of moisture and precipitation onshore
across the southern state.

Ensemble means are decently clustered with the pattern evolution
aloft through the medium range period as subsequent shortwaves
rounding the southern edge of the trough brings continued rain
chances and possible gusty winds along the north gulf coast.
Uncertainty emerges, however, as individual model solutions vary
significantly with embedded systems and interactions over time.
Meanwhile, periodic wet conditions continue for the Bering Sea and
Aleutians as the aforementioned trough shifts to the southeast
beginning on Saturday. From Sunday to Tuesday, another shortwave
trough moves from the Chukchi Sea southward into the eastern
Bering, potentially bringing another round of light to moderate
precipitation along the Southwest coast, while an upper ridge
builds across the western Bering.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...NONE.
FIRE WEATHER...NONE.

&&

SYNOPSIS AND MODEL DISCUSSION...VR
SOUTHCENTRAL ALASKA...EZ
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...PS
MARINE/LONG TERM...MK/MF