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000
FXAK68 PAFC 021301
AFDAFC

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
501 AM AKDT Thu Apr 2 2020

.ANALYSIS AND UPPER LEVELS...

The complex pattern of upper level features that has been with us
for several days churns on with an upper level ridge still in
place in the western Gulf and double upper lows in the north
Pacific interacting with a frontal boundary associated with a
Siberian low. Sensible weather has been fog and stratus in the
Kuskokwim Delta, rain and stratus in Bristol Bay, light snow in
the cold air behind the front in the eastern Aleutians, some rain
falling on the western edge of the Kenai Peninsula, snow showers
reaching into the Susitna Valley, and snow in the Anchorage metro
area.

&&

.MODEL DISCUSSION...

Model agreement for most features looks pretty consistent until
Saturday afternoon, where tracks for the Bering low begin to
deviate. However, does look like western Alaska remains in same
general flow pattern with various model solutions as the low
tracks ashore. The southerly extent of precipitation into Bristol
Bay could be of concern here, as well as precipitation types with
a long fetch of southwest flow.

&&

.AVIATION...

PANC...Expect light snow at the terminal. Low level flow will
shift to south- southwest during the day, so while snow will
remain light, ceilings will likely drop. Generally expect MVFR
conditions. If conditions do drop to IFR, it should be brief in
nature.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 and 2)...
An upper level trough will move into Southcentral today and
tonight. This will bring precipitation to the area, spreading from
west to east. Temperatures aloft are cold enough that
precipitation will generally be snow for inland areas. Surface
temperatures will be warm enough that accumulations will be
limited, and the snow may occasionally mix with some rain. Coastal
areas will see a mix of rain and snow, or possibly all rain. The
trough will push east of the area by Friday afternoon and a
short-wave upper level ridge will nudge into the area. Some clouds
and moisture will remain over the area as this ridge will be
"dirty", but chances of precipitation are fairly low.

&&

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

An upper level shortwave continues to move through the interior
part of Southwest Alaska this morning. In its wake, low level
stratus and fog have blanketed the coastal areas including the
Kuskokwim Delta coast and the Bristol Bay coast. Light snow
showers are tapering off over the Lower Kuskokwim Valley this
morning, though snowfall is expected to continue along the
foothills of the Alaska Range through this evening, with about 4
inches expected near Iliamna. The big challenge with this
forecast has been precipitation type, especially over the Bristol
Bay area. A mix of snow and rain will likely continue through the
morning across interior parts of Bristol Bay. Farther south over
the Alaska Peninsula, rain is expected to continue a bit longer
before tapering off this afternoon as moisture advection ceases in
the midlevels. By Friday, another system approaches Southwest
bringing a second round of mixed precipitation. Of note, winds
will also increase beginning Friday evening, especially along the
coast. With colder air initially in place at the surface and warm
air moving in aloft, the forecast challenge will once again be
determining precipitation type with this event as it moves across
the region Friday night into Saturday. As the low moves inland
over the Kuskokwim Delta coast, cold northerly flow on the
backside will return, forcing any lingering showers to fall as
snow late Saturday into Sunday. Expect colder temperatures and
onshore flow through the end of the weekend.

&&

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

Weak low pressure in the northern Bering continues to dissipate
and exit to the north through this evening. Another low approaches
the Bering today, with the leading front approaching the western
Aleutians this morning. Gusty southerly winds and rain will
spread in along the Chain as the front reaches the central Bering
by early Friday morning. The main change in the overnight
forecast with this system was a slight increase in winds across
the Bering as pockets of storm force winds are possible over the
south-central Bering waters Friday afternoon into Saturday. As
the low center moves into the northern Bering Saturday, cold
northerly flow will fill in on the backside, bringing much cooler
temperatures to the entirety of the Bering for Sunday.

&&

.MARINE (Days 3 through 5/Saturday through Monday)...

Bering Sea/Aleutians...
There is a high degree of confidence that widespread gale force
winds will occur across the Bering on Saturday and continue into
Sunday morning. Confidence is much lower with a weak low
developing in the western Bering on Sunday, then moving into the
eastern Bering on Monday, as guidance shows major discrepancies
with the placement and track of this low. As of now, the winds
associated with this weak low are expected to remain below gale
force and the compact nature of the low means the core of
strongest winds would affect a small area.

Gulf of Alaska...
The most significant weather for the Gulf will be strong cold air
advection across the Alaska Peninsula and into the Gulf. The best
estimate of timing is beginning sometime Saturday night and
continuing through the day Sunday. While the current forecast
advertises small craft advisory winds, there is good potential
that these winds could reach gale force, with storm force gusts
out of bays and passes along the Alaska Peninsula. These strong
northwesterly gap winds will also increase the chance of freezing
spray.

&&

.LONG TERM FORECAST (Days 4 through 7/Sunday through Wednesday)...

There is consistency with the general synoptic pattern across the
region on Sunday with an upper low over the Seward Peninsula and
an upper ridge over the eastern portion of the Alaskan mainland
near the AlCan border. This means temperatures will be generally
cooler to the west and warmer to the east. Forecast confidence
decreases into Monday as guidance shows a higher degree of
variation in the placement of the upper low as well as the
placement of the upper trough associated with this low. This is
significant because this means our confidence is lower in where
precipitation will occur and how intense the precipitation will
be across the Alaskan mainland. One area of consistency is that
due to the strong cold air advection expected with this trough,
the precipitation type will most likely be snow. Guidance shows
a more consistent synoptic set up across the area on Tuesday
with an upper trough over the Alaskan mainland while an upper
ridge is present across the Bering/Aleutians. Due to this, the
coldest temperatures are expected across Southcentral on Tuesday.
Confidence then becomes very low on Wednesday as guidance shows
a very high degree of variation between the upper level synoptic
pattern which will then influence the surface synoptic pattern.

&&


.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...Gale Warning 165 170 173 174 176 177 178 179 411 412 414.
         Storm Warning 175 413.
FIRE WEATHER...NONE.

&&

$$

SYNOPSIS AND MODEL DISCUSSION...LTB
SOUTHCENTRAL ALASKA...BL
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...KO
MARINE/LONG TERM...ED