Small Craft Advisory 393, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
408 PM AKDT Mon May 14 2018

.ANALYSIS AND UPPER LEVELS...
The upper level pattern consists of a broad trough encompassing
Mainland Alaska with ridging both upstream over the far western
Bering Sea and downstream over the northwest U.S. and southwest
Canada. The key features embedded within the Alaska trough include
a low exiting across the Yukon with a weakening deformation band
on the back side from western Prince William Sound to the Mat-Su,
a short-wave crossing the northern Gulf, and a very cold upper
level low over southwest Alaska with a short-wave rotating
inland. Area soundings generally show a weakly unstable
environment across the southern Mainland, with steepening lapse
rates over southwest Alaska as colder air advects in aloft.
Showers are focused along the old deformation band over
Southcentral, ahead of the trough moving inland over southwest
Alaska and right under the upper low center over the Kuskokwim
Delta coast. Out west, benign conditions dominate much of the
Bering Sea and Aleutians.

&&

.MODEL DISCUSSION...Models remain in good agreement with large
scale features over the next couple days. With many features
moving through the trough, the primary challenge is determine
areal coverage of showers, along with the most likely timing
of showers for any specific location. A secondary challenge is
precipitation type, as colder air crossing the southern mainland
causes a widespread drop in snow levels.

&&

.AVIATION...
PANC...While showers will generally remain in the vicinity, the
best chance for showers moving over the terminal looks to be
until 12Z as short-wave moves up Cook Inlet. Showers will likely
form along/near the Kenai mountains and move off the mountains
toward Anchorage. There could be a brief lowering of ceilings and
visibility (down to MVFR) with these showers. Otherwise, VFR
conditions will persist.

As far as winds, there may be a few southerly gusts this evening,
but overall Turnagain wind is weak. The wind will be stronger on
Tuesday as the coastal ridge builds ahead of a front moving into
the southern Gulf. This will lead to strengthen southeasterly
winds Tuesday afternoon into evening.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 through 3)...
The longwave trough and associated upper low over southwest Alaska
will keep southcentral under generally cool and cloudy conditions
for the next few days. As the low yesterday in the northern Gulf
has weakened and broken up, showers have developed around upper
Cook Inlet and along the north Gulf coast. These showers will
continue to slowly move northward overnight, and be reinforced by
another shortwave currently moving through the Bristol Bay zone.
Higher elevations of the Anchorage Hillside and up toward Hatcher
Pass may see some snow tonight or tomorrow morning as freezing
levels will be dropping. Some breaks of sun are likely by Tuesday
afternoon as cooler air moves into the area from the southwest.

By Wednesday southeast flow across the entire area strengthens, as
a weak but persistent wet pattern moves back into the coastal
areas around the Gulf. At this point the inland areas look like
downsloping will keep things much drier, but probably not totally
dry as the cross-barrier flow is not particularly impressive.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 and 2)...
A weakening cold front and associated low over the Kuskokwim
Delta area will push further inland while dissipating tonight,
leaving some lingering showers in its wake through Tuesday night.
West to southwest winds across the area will shift to the north
and east on Wednesday when the north Pacific low and associated
front begin to push into the Alaska Peninsula. This system will
bring another shot of warm and rainy conditions to the southwest
Mainland overnight Wednesday into Thursday.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 and 2)...
A weakening low pressure system along the eastern Bering advects
a colder air mass over the area through mid week, with showery
conditions tracking through the eastern Bering along the western
periphery of the upper low. A ridge build along the western
Bering this evening, keeping low clouds and patchy fog into
Wednesday. The next front moves to the western Aleutians Wednesday
morning returning rain and gusty southeasterly flow to Shemya.

&&

.LONG TERM FORECAST (Days 3 through 7)...
Beginning Thursday evening, models are in decent agreement showing
a persistent longwave ridge still centered over the NW US and the
west coast of Canada, extending north into the Yukon and eastern
portions of interior Alaska. At the same time, an upper level low
will continue to rotate over the west coast of Alaska with a
secondary low over the Northern Pacific south of the Aleutians,
which will begin to move north towards the Gulf of Alaska. The
interaction between the low and high will lead to a good push of
moisture and onshore flow towards coastal regions of Southcentral.
As this low moves north it will nudge the ridge east into
interior Canada allowing a steady stream of systems to rotate up
into southern Alaska. This means a continuation of the cloudy,
wet, and cooler than normal conditions over the region through at
least the weekend, delaying summer for a bit more.

Those looking for reprieve may have to wait until the middle-end
of next week as models are hinting at the persistent upper level
trough over the state shifting east allowing high pressure over
the Bering to move further east, bringing drier and warmer
conditions over most of the mainland, though models still vary
widely regarding the specific solution.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...None.
MARINE...None.

&&

SYNOPSIS AND MODEL DISCUSSION...SEB
SOUTHCENTRAL ALASKA...AMD
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...TP
LONG TERM...KVP