Small Craft Advisory 535, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
507 PM AKDT Sat Jul 11 2020

.ANALYSIS AND UPPER LEVELS...

A 500 mb low east of the Yukon Delta has been producing some
thunderstorms throughout the day in the Kuskokwim valley. This
upper level low will move southward through the next few days and
be the focus for thunderstorm activity this afternoon and evening,
and again Sunday. While Southcentral Alaska remains unstable and
conducive for thunderstorms today, they should be more widespread
in Southwest Alaska because of this upper level low.

The Bering Sea remains under high pressure causing low stratus
over the majority of it. A front along the Central Aleutians is
shearing apart as it runs into the ridge.

&&

.MODEL DISCUSSION...
Models are in good synoptic agreement through the early part of
next week with some more noise creeping into the pattern for the
second half of the week. This is most evident in the Bering Sea
where the GFS has a high in the central Bering and the ECMWF and
Canadian show a closed low in the southern Bering Sea. However,
this will mainly impact the Aleutian chain and the practical
difference may just be wind direction and whether there is
predominately fog or rain.

&&

.AVIATION...
PANC...
Winds have turned to the southeast this evening and could be gusty
at times off the Turnagain Arm. Showers will persist around the
airport into tomorrow, with some isolated thunderstorms around the
terminal this evening. Ceilings will drop under 5000 ft at times,
but should remain above MVFR conditions.

&&

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

The upper level low continues to drop south over western Alaska,
pushing ample moisture into the Southcentral region. This,
coupled with the unstable airmass, will produce isolated to
scattered thunderstorm activity across the Kenai Peninsula north
into the Susitna Valley and western Copper River Basin this
evening. The steering flow is out of the west, thus expect the
storms that do form to move to the east and mainly be along the
Talkeetna and Chugach Mountains. Some storms will form off the
Alaska Range as well and move across the Susitna Valley. Following
the convective activity tonight, west to southwest flow will
usher in more stable air along with more moisture, thus increasing
the chances of rain across much of south central Alaska Sunday,
particularly the Susitna Valley.

A surface low will be under the low over Southwest Alaska and a
surface low will form along a front south of the Alaska Peninsula
tonight. This low intensifies as it moves into the western Gulf of
Alaska Sunday night and Monday. In advance of this low a ridge
builds in the eastern Gulf of Alaska and intensifies Monday. The
interior thermal trough, while not strong, will be in place as
well. The combination of the intensifying ridge and interior
trough will be the driver behind the gap winds through the Chugach
Mountains as well as along the Copper River the next few days.

&&

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

An active pattern is set up across Southwest Alaska today as an
upper level trough digs into the region. Instability and
convection accompany this feature as it moves southward through
the end of the weekend. Thunderstorms have already developed over
the Kuskokwim Valley and interior Bristol Bay. Widely scattered
thunderstorms are expected to continue for interior locations,
with areas just north of New Stuyahok looking like a hot spot for
storms late this afternoon into the evening hours.

This pattern will continue into Sunday, though a bit weaker with
less thunderstorm activity expected as there is slightly less
instability in place. However, isolated thunderstorms remain in
the forecast, once again staying farther inland away from the
coasts. Quieter weather moves in to start the week on Monday with
showers tapering off across the Southwest.

&&

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

With high pressure across the Bering, fog and low stratus will
remain in the forecast over the next few days, with conditions
improving for the daytime hours. Low pressure continues to slide
eastward south of the Aleutian Chain, keeping relatively weak
winds with a chance of precipitation. However, there is some model
uncertainty start Sunday afternoon whether this area of low
pressure will develop into a closed low south of Kodiak Island,
which would bring more precipitation and stronger winds to areas
south of the Alaska Peninsula.

&&

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

High pressure lingers across the Bering with easterly winds and
waves across the southern half and southerly winds and waves over
the northern half through Thu. High uncertainty comes with the
initial position and track of a North Pacific low, bringing
problems its movement and wind directions with said low through
Thu. Confidence is good for less than small craft winds and waves
south of the Aleutians through Thu.

Over the Gulf, a low center will track across the Gulf, however
certainty is low for frontal positions through Thu. East to
southeast winds and waves are expected across the Northern Gulf
with less than small craft speeds. We expect a shift to northerly
winds and waves around Kodiak Island and the western Gulf by Thu.

&&

.LONG TERM FORECAST (Days 3 through 7)...
By Tuesday, the upper level low that is near Southwest Alaska
today will have moved over Kodiak Island and be in the central
Gulf of Alaska. This will start the period with high pressure over
Southwest Alaska and a front along the north Gulf coast. The high
pressure is not terribly strong but should spread over
Southcentral Alaska for the middle of next week. Southwest Alaska
will be susceptible for low stratus to advect into the region off
the Bering Sea, though rainfall should mainly be afternoon and evening
showers over higher terrain.

Afternoon and evening showers are also likely over interior parts
of Southcentral Alaska throughout the period.

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

&&

SYNOPSIS AND MODEL DISCUSSION...EZ
SOUTHCENTRAL ALASKA...SA
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...AH
MARINE/LONG TERM...MK/EZ