Small Craft Advisory 372, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
246 PM AKDT Sat May 2 2020

.ANALYSIS AND UPPER LEVELS...
A weak easterly wave is moving west across the eastern Gulf.
Clouds, a few showers, and slightly increased offshore flow are
about the extent its influence. The remainder of Southcentral,
including Kodiak Island, is generally in fair skies with local
sea breezes. Broad offshore flow with high pressure inland is
bring generally fair skies and generally dry conditions to the
Southwest Mainland. Upper level trough and weak surface centers
brought widespread clouds and showers to the Bering Sea and
Aleutians.

&&

.MODEL DISCUSSION...
Models overall are in good synoptic agreement into Tuesday. The
main area of value added grid edits will be in the pressure driven
local effect wind areas. High Res model will be used in addition
to hand edits to capture these effects.

&&

.AVIATION...
PANC...VFR conditions with light and generally northerly winds
are expected.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 and 2...Sun and
Mon)...
Offshore flow will continue Sunday with gap winds through the Mat
Valley, Valdez, Thompson Pass, the Copper River Valley and the
Copper River Delta remaining gusty at times. This pattern will be
met with warm and dry conditions across southern Alaska. A second
upper level shortwave looks to head our direction late Sunday
which will bring chances for precipitation to Southcentral. Due to
a barrier jet forming across the northern Gulf, expect an
increase in Turnagain Arm winds and downsloping. There is still a
chance for precipitation in Anchorage during this time, however,
the best chances are in higher elevations and locations along the
coast. The increase in cloud cover will up humidities across the
region and slightly lower high temperatures in the afternoon and
increase low temperatures at night.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 through 3)...
Temperatures will continue to run 5 to 10 degrees above normal
for the region. The Kuskokwim River has been breaking up and at
least one ice jam has been detected. The western portion of the
Kuskokwim is under a flood watch from Tuluksak to Bethel. Further
upriver is under a flood warning. This is a very serious
situation that is unfolding and is being actively monitored.
Temperatures will warm well into the 50s across all of Southwest
Alaska Sunday, with the warm temperatures continuing into Tuesday
under mostly sunny skies. The warm temperatures will only
increase snow and ice melt rates. Sunday a shortwave with move
from Katmai National Park to Togiak. It has an inverted trough
with it and this feature may produce isolated shower. But these
showers are predominately expected south of the Kuskokwim River.
Monday afternoon, the NAM model is pinging into 200 J/kg of CAPE
(Convective Available Potential Energy), slightly negative Lifted
Indices and Total Totals of +50...all of which suggest
thunderstorm potential from Iliamna to Goodnews Bay.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 and 3)...
On the latest ASCAT (advanced scatterometer)there is a weak low
south of the chain southeast of Adak, a trough southwest of Attu
Island and high pressure over the western Bering. On the CIMSS
Natural Color RGB satellite image there is some stratocu and a few
patches of low stratus but there are some blue skies too. Light
precipitation and gusty winds will impact the Western Aleutians as
a low moves into the region but otherwise it is a pretty mild
forecast package from the Central to Eastern Bering.

&&

.FIRE WEATHER...
Offshore northerly winds will continue this afternoon across
Southwest Alaska. This will cause relative humidity values to fall
to between 20 and 30 percent over much of the region. RH should
recover over night. The breezy winds and low relative humidity
values are expected again tomorrow. The models are hinting at
unstable conditions setting up over portions of SW AK on Monday.
We will have to see if this trend continues with the models. But
as is looks right now there is potential for isolated
thunderstorms on Monday afternoon and evening.

&&

.MARINE (Days 3 through 5: Tuesday through Thursday)...
Gulf of Alaska: There is still some model uncertainty with the
low over the Gulf on Tuesday through Wednesday afternoon in terms
of position and strength. The forecast will mostly likely keep
small craft advisory winds over the northern Gulf, with the
potential for a small area of gale force winds if models lock onto
a stronger solution. Models are in better consensus with the next
North Pacific low lifting northward on Thursday morning, which
will bring widespread small craft advisory level winds to the
Gulf, which some models are hinting at a stronger solution
introducing gale force winds across this area.

Bering Sea: Model runs are in relatively good agreement today
with a front moving across the western Aleutians and Bering
Tuesday afternoon, which will continue eastward over the central
Bering and diminish by Thursday morning. However, there is still
some uncertainty as to whether this front will reach gale force
potential like the GFS run currently has forecasted.

&&

.LONG TERM FORECAST (Days 4 through 7: Wed through Sun)...
As a front associated with the low in the Gulf on Wednesday lifts
northward, the potential for shower development is possible on
Thursday along the North Gulf Coast and even for some inland
locations across Southcentral. A second front on Friday morning
will bring more widespread precipitation from Kodiak Island and
the Kenai Peninsula, which will eventually spread into Southwest
Alaska by Friday afternoon. However, there is some uncertainty in
the track of this system and how quickly it will clear out. Behind
this system, upper level ridging will move in over mainland
Alaska, favoring above average temperatures for the region. There
are some differences in the strength of this ridge, but will
likely result in temperatures in the upper 50s to low 60s for most
inland locations for later this week into the weekend.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...Flood Warning 155 152 (Kuskokwim River).
 Flood Watch 155.
MARINE...NONE.
FIRE WEATHER...NONE.

&&

SYNOPSIS AND MODEL DISCUSSION...RC
SOUTHCENTRAL ALASKA...CK
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...PJS
MARINE/LONG TERM...AH