Gale Warning 523, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
431 AM AKDT Tue Oct 20 2020

.ANALYSIS AND UPPER LEVELS...

Lingering snow showers remain around the Copper River Basin this
morning as a broad upper level low continues to exit into the
Gulf. Behind this feature, ridging is starting to build in over
the Southwest coast, allowing fog and low stratus across the
Kuskokwim Delta to spread eastward into the Kuskokwim Valley for
this morning. A tight pressure gradient between these features is
allowing for strong outflow winds south of the Alaska Peninsula
and the North Gulf Coast.

Upper level ridging continues across the central and eastern
Bering and Aleutians, keeping relatively quiet weather conditions.
Farther west, a digging trough over the western Bering is helping
to amplify this ridge pattern. A low in the North Pacific
positioned south of Dutch Harbor this morning will be the next
significant weather maker to keep an eye on over the next several
days as it lifts northward into the forecast area.

&&

.MODEL DISCUSSION...

Run to run model consistency continues for the two lows developing
south of the Alaska Peninsula and Aleutian Chain Tuesday through
Wednesday, keeping higher confidence of storm force winds over the
eastern Bering on Wednesday. There is, however, a bit of
disagreement with the timing and how far north the associated
front lifts into Southwest Alaska starting on Thursday, which
impacts timing of precipitation that could make it into
Southcentral Alaska for Friday.

&&

.AVIATION...

PANC...VFR conditions and light winds persists. Low stratus
and/or fog could form early this morning for Anchorage and the
vicinity, which would improve by late morning.

&&

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

An upper short wave dropping south across the Eastern Mainland
will continue the chance of light snow across areas of the Copper
River Basin today. Light snow should end as drier air moves in
tonight.

An inverted surface trough over the Gulf waters in combination
with cooler air spilling in over Southcentral (predominately the
Copper River Basin/inland) will strengthen the thermal and
pressure gradients and give rise to brisk gap and outflow winds
across the North Gulf Coast and Eastern Kenai Peninsula. Winds in
these areas will likely peak overnight and diminish slowly
Wednesday as gradients relax some. Gusty winds which develop over
the Matanuska Valley tonight will likely linger into Wednesday
night. A weather front moving north on Wednesday brings gales and
increasing chances of rain to the Western Gulf/Kodiak Island late
Wednesday.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 through 3: Tuesday
morning through Thursday morning)...

High pressure will dominate the area today, with the fog and
stratus across the YK Delta this morning area clearing out by the
afternoon. Clear and colder temperatures move in Tuesday night,
but not expecting as much fog for Wednesday morning with drier air
moving in from the northeast and increasing winds. Wednesday will
be dry across the Southwest, however, an approaching frontal
system will bring increasing winds and moderate to heavy rain to
the AKPEN by Wednesday afternoon. This frontal system will slowly
move into the Bristol Bay region Wednesday night through Thursday
morning. This system will bring storm force winds over the water
and strong winds over the AKPEN and near coastal land areas of the
Southwest.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 through 3: Tuesday
morning through Thursday morning)...

High pressure will continue across the region today with
increasing winds up to gale force Tuesday night into Wednesday
morning across the Aleutians as a frontal system moves north
towards the Aleutians. A complex low pressure system will push the
front northward on Wednesday with moderate to heavy rain across
the Aleutians and winds increasing to storm force across the
eastern Aleutians. These storm force winds will move into eastern
portions of the Bering Sea and Bristol Bay by Wednesday evening,
weakening by Thursday afternoon. As the low pressure pushes north
Thursday morning, winds will decrease across the central and
eastern Aleutians to small crafts, with areas of gales still
across much of the western Bering and Aleutians.

&&

.MARINE (Days 3 through 5: Thursday through Saturday)...

Gulf of Alaska:

A well developed front moves across the Gulf through Sat. The
track and development vary considerably, but widespread easterly
gale force winds and waves will spread across the Gulf through
Sat. The area of gale force winds retreat to around Kodiak Island
Sat, leaving small craft winds over the Gulf slowly diminishing
through Sat.

Bering Sea:

A North Pacific low and front moves into the Central Bering
through Sat. Track and development of the system vary
considerably, but overall area coverage looks reasonable, with
easterly gale force winds and waves spreading into the Bering.
High end gale winds expected in Bristol Bay near Alaska Peninsula
channeled areas. The winds wrap the low bring a second round of
gale force winds across the Eastern Aleutians Fri. The entire
system slowly diminishes to small craft winds Sat.

&&

.LONG TERM FORECAST (Days 3 through 7: Thursday through
Monday)...

At the onset of the forecast period there is a ridge axis that
spans from the East Pacific across Kodiak and north of the Brooks
Range. Additionally, there is a robust low over the central
Aleutians. The leading edge of the precipitation shield will be at
the door step of Dillingham, King Salmon and Kipnuk. 48 hrs
later, the ridge axis is just east of Cordova and the upper level
low anchoring the aforementioned system is near the Pribilof
Islands. However, this pattern will result in broad southwest
flow over much of South Central and the precipitation shield will
have moved eastward. At this time, it is still too far out to
tell whether the front will bring any rain/snow to the Anchorage
area. The front will most definitely get sheared by the western
Alaska Range. Showers will linger over the Bering in association
with the remnants of the occlusion. In its wake, a new front will
emerge from the North Pacific. The precipitation shield will begin
to impact Attu Island and Shemya Saturday night.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...Storms 150 155 172.
         Gales  127 128 130 138 160 165 170 171 173-180 411-414
FIRE WEATHER...NONE.

&&

SYNOPSIS AND MODEL DISCUSSION...ALH
SOUTHCENTRAL ALASKA...RMC
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...RC
MARINE/LONG TERM...MK/PS