Small Craft Advisory 245, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
436 PM AKDT Thu Mar 22 2018

.ANALYSIS AND UPPER LEVELS...
There is an upper level high over southern Alaska this afternoon.
There is a surface high centered over east central Alaska nudging
into the Copper River basin, with fairly strong offshore flow
over Southcentral. There is a large upper low centered over the
western Bering Sea. An associated surface front stretches from the
Alaska Peninsula north through the coastal portions of the
Kuskokwim Delta. Snow and blowing snow are occurring along the
Kuskokwim Delta coast, with rain further south over the eastern
Bering and Alaska Peninsula. Plenty of showers behind this front
are evident over most of the Bering Sea and Aleutians.

&&

.MODEL DISCUSSION...
The numerical models are in good agreement for the short term
portion of the forecast (Saturday afternoon). Some differences
begin Friday night with a surface low crossing the central and
western Aleutians that moves into the Bering on Saturday, but
these are fairly minor. Forecast confidence is therefore above
normal.

&&

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

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 and 2...Fri and
Sat)...
Winds will slowly decrease this evening as the ridge axis continues
to bull its way over southern AK. The upper level energy will
continue to drift east out of the Gulf overnight while the thermal
gradient relaxes simultaneously. Winds appear to have peaked
through Thompson Pass and Valdez earlier this morning and should
continue to slowly diminish now. As is often the case, they are
"exceeded expectations" in Whittier and Seward where gusts
continue to reach near 45 mph. These too should slowly fall off
through the evening.

Then attention shifts to a weak front approaching the area from
the west on Fri. This front is "washing out"/falling apart as it
crosses the AK Range. However, it does still look like a rapidly
moving shortwave will bring enough energy to keep a chance
rain/snow for Kodiak Island in the forecast. This front will
produce a surface low over the Northern Gulf of AK late Fri into
Sat. This will result in another round of offshore flow across
southern AK with some more cold air advection wrapping around the
backside of the low. However, this event will be much weaker than
the ongoing one through many of the usual gaps (Valdez, Thompson
Pass, Matanuska Valley, etc). It appears the best support will be
for strong northwest flow near the Barren Islands and Shelikof
Strait. Gale warnings have been hoisted for the Barren Islands.
These winds will be quite short-lived coming down already by late
Sat morning. After that, weather will remain relatively quiet with
just slowly increasing clouds as the next front approaches from
the southwest Sun.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 and 2)...

The front moving onshore the Kuskokwim Delta coast this afternoon
will slowly progress inland over the next 24 hours or so. The
front is weakening, so there is not a lot of warm air still being
transported into the area. As a result, even most of the
population centers around the Bristol Bay zone should stay cold
enough for snow. Most places will see a quick 1 or 2 inches with
not much potential for higher amounts except over the Lower
Kuskokwim Valley where continued slowing of the front may allow
for slightly higher snow amounts. The north Delta Coast is seeing
significant blowing snow at the moment, but this should be
diminishing rapidly as the front starts to fall apart this
evening. Weak high pressure/ridging moves into the area for the
end of the week and first half of the weekend, which should allow
for some breaks of sunshine and fairly typical springtime
temperatures across the area.

&&

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

The large storm over the northern Bering is generating significant
storm-force winds north and west of Saint Matthew Island today,
but the good news is this storm is quickly moving northward and
away from the area. Moderate cold advection, gusty winds, and snow
showers are evident on satellite imagery across much of the rest
of the Bering. These conditions will continue through the day
Friday, but by Saturday morning the next storm will cross into the
region from the western Aleutians. This next storm looks to be
strong enough to produce some gale-force winds, but overall should
be a fairly typical storm strength as it continues tracking toward
the Pribilofs by the end of the weekend.

&&

.LONG TERM FORECAST (Days 3 through 7)...
A brief pattern change will begin on Sunday, as the ridge in the
North Pacific weakens slightly and moves southward. This will
allow the low pressure systems that have been remaining in the
western portion of the area to move eastward, affecting more of the
mainland. On Sunday, a triple point low will develop along the
front south of the Aleutians, then strengthen as it moves into the
Gulf of Alaska. This will bring weather onshore for the Gulf Coast
region. However, the system will weaken rapidly as it heads
northward over the mainland and precipitation will diminish for
interior regions on Monday. By Tuesday, forecast continuity
between the model solutions begins to struggle. Earlier runs
indicated that the ridging would build back in to the North
Pacific, which would bring a very spring-like pattern to the
forecast area. However, this afternoon's runs have diverged,
instead bringing a strong low into the Gulf of Alaska. This brings
low confidence to the extended forecast for today

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...None.
MARINE...Storm 185. Gales 127 128 130 131 177 411 412 None.

&&

SYNOPSIS AND MODEL DISCUSSION...BL
SOUTHCENTRAL ALASKA...MO
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...AD
LONG TERM...LF