Small Craft Advisory 880, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
453 AM AKST Fri Nov 9 2018

.ANALYSIS AND UPPER LEVELS...

Gale force winds associated with a strong low approaching Saint
Lawrence Island this morning are ongoing across nearly all of the
northern Bering Sea north of the Pribilofs this morning. Somewhat
colder air from off of Russia is overspreading the same areas,
leading to scattered snow showers across the region. The leading
edge of that activity is moving into Southwest Alaska this
morning, briefly lowering ceilings and visibilities as the
individual showers pass through. Since that cold air has moderated
quite a bit after crossing the relatively warm waters of the
Bering, surface temperatures across Southwest Alaska are largely
above freezing outside of the Lower Kuskokwim Valley. The leading
edge of the cooler air mass is crossing the Alaska Range, which is
the reason clouds are increasing across portions of Southcentral
this morning. Meanwhile the low which brought rain to Cordova and
snow to Valdez and Glennallen has moved into the eastern Gulf,
resulting in a couple hundred miles of relatively clear skies
between it and the advancing front moving over the Alaska Range. A
weak area of low pressure tracking south of the central Aleutians
will help draw a much stronger low currently over the central
Pacific northward, which will be the main weather maker for
southern Alaska this weekend.

&&

.MODEL DISCUSSION...

The models are in reasonably good agreement through the short-
term, with the low over the northern Bering expected to wrap back
southward on Saturday, meeting up with a low moving northward out
of the north Pacific near the Alaska Peninsula on Saturday
morning. All of these features merge into one strong low over the
eastern Bering by Sunday morning. While there is good agreement
that all of the above occurs, the details of how and when all of
this happens are still very uncertain. The details are important
because the North Pacific low is expected to bring much warmer air
northward along with it, which will help to quickly change the
snow at the leading edge of it over to rain. Thus, overall large-
scale forecast confidence is high but individual details
confidence is much lower.

&&

.AVIATION...
PANC...VFR conditions and light winds will persist. There is a
very slight chance of a snow shower or two late this morning into
this evening, but any that form are unlikely to worsen
conditions.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 through 3)...
A trough pushing through Southcentral Alaska today will bring
a chance of light snow to the area, primarily in the mountains.
Most low lying areas should not see much, if any, new snow.
Ridging will then build in later today helping to clear out cloud
cover brought in by the trough. However, these conditions will be
short lived as a new system approaches the Gulf from the south.

The front associated with this new system will impact Kodiak
Island Saturday morning and make it to the north Gulf Coast by
Saturday evening. This system is pulling up warm air and a long
fetch of moisture resulting in a fair amount of rain for locations
all along the north Gulf Coast. Some locations further inland and
at higher elevations will at least start off as snow before
transitioning to rain. Most of the precip will be stopped by the
coastal mountains with areas beyond the coastal ranges expected to
see minimal precip. The system will also bring stronger winds to
the gaps for areas along the north Gulf Coast and the rain and
winds look to last through Sunday.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 and 2)...
The upper level trough pushing into Southwest Alaska will
continue to push cold air and snow showers inland today before
tapering off overnight. The low level flow will turn easterly on
Saturday with very strong east to northeast winds increasing
rapidly ahead of a strong North Pacific frontal system tracking
up from the south. The main front will reach the Bristol Bay area
Saturday afternoon and continue to lift north over the Kuskokwim
Delta and Kuskokwim Valley through Saturday night. A secondary
frontal wave will lift north over the area Sunday and Sunday
night.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 and 2)...
A cold upper level low tracking off of the Kamchatka Peninsula
will swing a trough through the Western Aleutians this afternoon
and Central Aleutians tonight, while the upper low center tracks
east to the central Bering. The trough will continue to dig south
towards the North Pacific on Saturday as a strong north Pacific
low tracks north towards the Alaska Peninsula in response. The
deepening surface low will cross the Alaska Peninsula around
Saturday afternoon and then curve back to the west Saturday night
and then track south across the Eastern Aleutians on Sunday.

&&

.LONG TERM FORECAST (Days 4 through 7/Sun night through Thu)...

The longer term forecast starts out in a very active pattern late
Sunday with a large and complex low centered in the Eastern
Aleutians with a secondary center along the front in the western
Gulf of Alaska. There is a col between these lows but a tight
pressure gradient along the front curving out of the Gulf of
Alaska...into Southcentral and Southwest Alaska and then through
most of the Bering Sea. The main low will take a round-about
route into the Gulf of Alaska through the middle of the week and
then into Southeast Alaska Thursday. While this is a rather
complex low and track, the good news is that there is fairly good
agreement on models, especially in the synoptic features, which
brings increased confidence in the main elements of the forecasts.

This pattern is bringing some very warm air to the southern mainland
and southeast Bering Sea for the start of the week. Therefore there
will be some windy and rainy areas which then will transition
back to snow showers with cooling temperatures aloft. The cold air
which was displaced to the northwest by this system will move
back over the region quickly in the Monday to Monday night
timeframe as the low further occludes and moves eastward. By next
Thursday, the mainland part of the state will once again be under
an upper level trough with a ridge over the central Bering Sea
leaving the area in generally dry pattern with seasonal
temperatures.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...High Surf Advisory: 155.
MARINE...Storm Warning: 138 150.
Gale Warning: 120 130-132 136 137 139 155 160 165 175-178 180-185
351 352 411-414.

&&

SYNOPSIS AND MODEL DISCUSSION...JPW
SOUTHCENTRAL ALASKA...DK
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...JR
LONG TERM...EZ