Small Craft Advisory 754, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
430 PM AKDT Sat Oct 3 2020

.ANALYSIS AND UPPER LEVELS...

The pattern remains amplified with a deep upper trough over the
Bering/Aleutians and a strong upper ridge extending from the
southwestern U.S. to Northwest Territory. The jetstream is
currently oriented from southwest to northeast, extending from the
midlatitude central North Pacific into northern British Columbia
and southern Northwest Territory. A developing area of low
pressure is currently near 49N 161W and is moving northeastward.

Closer to the surface, radar imagery shows showers moving
northward across the northern Gulf into Prince William Sound.
Showers are also moving northward across the Kenai Peninsula into
the Anchorage Bowl and the Mat-Su Valley. Radar also shows showers
moving northeastward across Bristol Bay and the Kuskokwim Delta.

&&

.MODEL DISCUSSION...

Guidance is in good agreement with respect to the placement and
intensity of synoptic scale features over the next 3 days, thus
forecast confidence is above average. With respect to the low in
the northern Gulf Sunday night into Monday morning, the NAM
appears to be the outlier with the placement of the low as the
NAM's solution has the low farther east (towards Yakutat)than the
rest of guidance. The rest of guidance has the low near the Copper
Delta Monday morning when the low moves inland.

&&

.AVIATION...
PANC...VFR conditions will persist. Gusty southeast winds across
the airport complex with diminish later this evening.

&&

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

Multiple shortwaves continue to rotate around the broad area of
low pressure that is still over the southwest coast. This
continues to bring showery conditions across Southcentral, as
seen on radar, which will continue through tonight. As a result,
flood potential remains for the Kenai River at Kenai Keys, the
Kenai River at Cooper Landing and for Trail River near Lawing.
Winds will remain gusty, through the remainder of the evening and
into tomorrow, for portions of the Gulf, Turnagain Arm, the Knik
Arm and the Copper River Basin. Along with this, we are still
seeing gusty conditions across Ted Stevens airport. Tonight, patchy
fog is a possibility over Cook Inlet as a weak ridge sets up over
the area.

By tomorrow morning, another deep low will enter the southern
Gulf. Models continue to struggle with the path of this low,
undecided how close to Kodiak Island the low will traverse as it
moves towards the northeastern Gulf coast. For now, it looks as if
it will move a bit further east from this morning, keeping gales
in Shelikof Strait. Storm force winds are anticipated around the
low, tomorrow morning through tomorrow night. Initially, they will
be across the Gulf coast waters, as a barrier jet, from south of
Cordova to southwest of Seward. Thereafter, a small swath of
storms will move across the central Gulf. The heaviest rainfall
will accompany this barrier jet with coastal locations seeing the
highest precipitation values. This will continue the concern for
flooding in the aforementioned areas.

Monday, this low pressure system will exit into Juneau waters,
with gale force winds remaining over the central and southern Gulf
before they dissipate to small crafts during the afternoon.
Chances for precipitation will remain over the coastal locations,
albeit significantly lighter than what will occur on Sunday.

&&

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

Scattered showers are currently moving south to north across the
region as a low departs to the north. Patchy fog may develop
overnight near the Kuskokwim Delta coast in a weak, southerly
flow. Relatively drier air will move in by Sunday morning ending any
lingering precipitation. The quiet pattern will continue into
early next week, although isolated showers will remain possible
over the Kuskokwim Delta under passing weak shortwave troughs.
Temperatures will gradually fall over the coming days as northerly
flow begins to develop.

&&

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

Showers will track west to east across the Aleutians through early
next week in a general northerly flow pattern. Benign conditions
are expected in the wake of the showers, north of high pressure. A
strong front will approach the western Aleutians Monday evening,
bringing moderate to heavy rain and gusty southerly winds tracking
west to east into mid next week.

&&

.MARINE (Days 3 through 5/Tuesday through Thursday)...

Bering/Aleutians

Early Tuesday southeast winds ramp to gale force across the
western Bering/Aleutians along with widespread rainfall due to an
approaching Kamchatka low. Wind/rain spreads into central
Bering/Aleutians mid to late Tuesday. Early Wednesday, the
Kamchatka low migrates towards the northwestern Bering, with
westerly small craft/low end gale force winds expected across the
western and central portions of the Bering/Aleutians. Eastern
areas of the Bering/Aleutians see southerly winds increase to near
gale force along with plentiful rain. Late Wednesday the low in
the northwestern Bering weakens, with winds turning westerly and
decreasing to small craft levels. Thursday, this area of low
pressure continues to weaken near St. Matthew Island with west-
southwesterly winds at small craft advisory levels expected across
much of the Bering/Aleutians.

Gulf of Alaska

Light westerly flow is expected Tuesday and Wednesday. On
Thursday winds will flip to southerly, with some small craft level
winds expected across the Western Gulf.

&&

.LONG TERM FORECAST (Days 3 through 7/Tuesday through Saturday)...

A low centered in the northern Gulf on Tuesday morning will slowly
move eastward and out of the Gulf by Wednesday night. Guidance is
in good agreement with the placement and intensity of this low.
An upper level ridge will move over the Gulf and Southcentral in
the wake of this low on Thursday which will result in less cloud
cover and warmer temperatures. An upper level low will move off
Siberia into the northwestern Bering Sea Thursday morning. This
low will then move into the central Bering on Friday. There is a
high degree of uncertainty with respect to this low on Saturday as
there are significant differences in solutions with respect to
the placement and intensity of this upper low. The one area of
consistency on Saturday is the upper trough associated with this
upper low will extend over the western Gulf and into Southcentral.
This will support cooler temperatures across Southcentral and
Southwest Alaska next weekend.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...Flood advisory 121 125. Flood watch 121.
MARINE...Gales 119 120 130-132 139 351 352.
FIRE WEATHER...NONE.

&&

SYNOPSIS AND MODEL DISCUSSION...ED
SOUTHCENTRAL ALASKA...CK
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...AP
MARINE/LONG TERM...MK/ED