Small Craft Advisory 296, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
416 AM AKDT Wed Apr 1 2020

.ANALYSIS AND UPPER LEVELS...

A persistent upper level ridge remains over the western Gulf of
Alaska and extends into the Matanuska Valley with a cutoff stacked
low in the north Pacific to its west. A longwave upper trough in
the Bering is pushing enough moisture over the ridge to get some
bands of snow in southwest Alaska, the Kuskokwim Delta and Kodiak
Island. Farther east on the Kenai Peninsula the ridge has shifted
and snow is falling in Seldovia and Homer. Further west on the
Alaska Peninsula and eastern Aleutians temperatures in the upper
30s are keeping rain with fog and stratus in the blend, as a long
fetch southwesterly component on the east side of the Bering Sea
trough pushes through.

&&

.MODEL DISCUSSION...

Models remain in lockstep with their evening runs. Precipitation
types are going to remain a concern as discussed last evening,
especially given the cooler seasonal temperatures battling it out
with longer days.

&&

.AVIATION...

PANC...VFR conditions and light winds will persist.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 and 2)...
An upper level high over the area will slowly slide eastward
through Thursday night. This will open up moist southwesterly
flow aloft. Considerable clouds will be over much of Southcentral
today, with increasing chances of precipitation into Thursday from
southwest to northeast. On Thursday and Thursday night an upper
level trough will push into the area from the west, bringing
precipitation to most areas. This precipitation will likely be in
the form of snow for most inland areas as temperatures aloft
remain fairly cool. However, daytime temperatures on Thursday will
generally be above freezing, so some rain mixing in is possible.
For coastal areas the likelihood of the precipitation mixing with
or changing to rain is higher.

&&

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

A weak closed low is currently sitting just west of Bristol Bay
early this morning. This low will continue moving north coming
onshore somewhere near Cape Newenham and then continuing north
into western Alaska. This will continue to bring light snow and
gusty winds to the region this morning. As this system continues
moving north it will bring warmer air, especially to the regions
that the winds shift to the southeast direction, in particular
(King Salmon and possibly Iliamna). The extent of how far north
this warm air gets is still somewhat questionable but left the
rain/snow mix for Iliamna in this package. King Salmon has a much
better chance of changing to all rain late this morning and
continuing through early Thursday.

Southwesterly flow aloft will continue through Thursday afternoon
and evening. This will continue until the front in the upper
levels swings through the region which will bring an end to the
precipitation. As this is approaching, more moisture will be drawn
northward along the Alaska Range/Aleutian Range keeping the high
pops in the forecast through Thursday afternoon and evening.
Following this will be a brief but strong shot of cold air for
Wednesday night.

Another upper level shortwave will move across the northern Bering
Thursday that will bring another round of snow Thursday afternoon
and evening.

A very brief lull in the weather is expected Friday as a weak
upper level ridge builds in before the next system quickly
approaches late Friday bringing the next round of weather.

&&

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

A weak closed low will continue moving northward through the
eastern Bering towards Cape Newenham and then onshore into western
Alaska.A developing inverted trough will keep light rain in the
forecast from Sand Point east tonight into Thursday.

A potent upper level shortwave will track through the Bering
tonight through Thursday. This system will bring gale force winds
to the western and central part of the Bering.

The next system will drive up from the North Pacific into the
Western Aleutians late Thu into Fri. This looks to be a storm
force low so kept the storm force wind gusts in the forecast and
nudged up the sustained winds more as guidance is showing
sustained strong gale force winds. It will also bring very warm
air (850 mb temperatures at 6C) and widespread moderate rain.

&&

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

Bering Sea/Aleutians...
A large and strong storm system approaches the Bering from the
North Pacific on Friday. There is a fairly large disagreement with
respect to how fast the system is moving, though there is
consistency with the system tracking northeastward from the
western Bering/Aleutians into the central Bering. Gale force winds
are expected Friday afternoon and evening across the western
Aleutians. There is low to moderate confidence that these gale
force sustained winds will reach the central Aleutians. Confidence
in the overall forecast rapidly degrades on Saturday as large
discrepancies exist between guidance. The forecast challenge
during this period will be the location of gale force sustained
winds as different solutions show gales, however they show these
gales are in different portions of the Bering.

Gulf of Alaska...
Uncertainty increases on Friday as solutions show a weak low
developing in the northern Gulf, though solutions vary with the
placement and intensity of the low center. There is a chance that
this low will produce gale force northwesterly gap winds at times
through the straits in the western Gulf on Friday. There is low
confidence in the wind forecast on Saturday, especially across the
western Gulf as solutions show significant differences in a low
over the central to eastern Bering.

&&

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

The upper ridging over the Bering is expected to move over the
Alaskan mainland on Saturday which will result in quiet weather
across the area. This upper ridging will not last long as guidance
is consistent with a second upper trough moving over the Alaskan
mainland Sunday afternoon. There is a high degree of variation in
the magnitude of this incoming upper trough but we can infer this
will mean colder than normal temperatures for the region. Guidance
shows the upper trough remaining in place over the Alaskan mainland
on Monday and Tuesday which will allow for these cold temperatures
to continue across the area.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...Gale 178, 411, 412.
FIRE WEATHER...NONE.

&&

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