Small Craft Advisory 387, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
432 PM AKDT Fri May 11 2018

.ANALYSIS AND UPPER LEVELS...
The remnants of the front that brought widespread heavy rain to
the Eastern Kenai Peninsula overnight as well as strong gap winds
to the Gulf Coast has made landfall near Prince William Sound,
leaving widespread shower activity in its wake. These showers are
largely being driven by a broad area of cold air has that has
advected around a low in the Eastern Bering, and is beginning to
move back northward to Cook Inlet and the Gulf Coast. This
actually helped produce some heavier band of showers over the
Anchorage Bowl late this morning as the cold air advection moved
through the moist post-frontal environment, but these are
beginning to diminish in intensity as the strongest advection
lifts to the north. These showers are also beginning to develop
further to the west over Bristol Bay, which will spread northward
into the Kuskokwim Valley in this afternoon. Along the southern
edge of this low, a deformation band is bringing widespread
rainfall to the Eastern Aleutians and AKPen, which will begin to
slowly weaken as the Bering low slowly moves to the north and
fills.

&&

.MODEL DISCUSSION...
The models remain in very good synoptic scale agreement through
Saturday with the remnants of the Bering low as is slowly weakens
over the next 2 days. The primary differences in the models
impacting forecast confidence have been with the low track of a
North Pacific low moving into the Gulf on Sunday. Previous runs of
the NAM especially brought this low much further east than the
rest of the guidance and were treated as an outlier. Agreement is
now beginning to improve with the 18z NAM, which came in
significantly further west, allowing for POP's to be increased
(especially along the Gulf Coast) for the afternoon forecast
package with good confidence.

&&

.AVIATION...
PANC...The strength of the SE winds and rain showers passing
through the terminal will be the primary forecast concerns through
Saturday morning. The heaviest showers should occur this afternoon
and evening, but more than likely will not produce MVFR ceilings
again as they did this morning. The strongest SE winds are also
expected to occur through this evening, which will then slowly
diminish during the overnight hours as the pressure gradient
along the Chugach begins to weaken, and then likely return
Saturday afternoon.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 and 2)...
Showery conditions will continue over much of southcentral Alaska
through early this evening while quickly tapering off in both
intensity and coverage. Persistent south to southwest flow aloft,
accompanied by colder air, will continue to keep some shower
activity over the area through Saturday night. After a brief
reprieve from the showery conditions Saturday night into Sunday
morning, the next system will track into the Gulf and bring
another round of precipitation to the area through Monday morning.

Gusty winds along Turnagain Arm and over the Copper River Basin
will begin to weaken tonight, as the weakening low out west begins
to track further north. However, gusty conditions are expected to
linger through turnagain arm and northern Cook Inlet through
Saturday.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 through 3...Fri
night through Mon morning)...
Low pressure off the west coast will continue to spin as it
drifts north from Kuskokwim Bay to southeast of Saint Lawrence
Island through Monday. Wind gusts along the coast will diminish
through the overnight hours as the low fills in and decays.
However, the persistent moist, cyclonic flow wrapping around this
system will continue to produce widespread clouds and scattered
precipitation for the region, especially in favored upslope
locations. Tomorrow afternoon, the first of a series of upper-
level shortwave troughs will move across southwest Alaska. This
will enhance precipitation across the area and bring in enough
colder air to produce a mix of rain and snow showers. A second
system moving through Sunday evening will bring another round of
cooler air and mixed precipitation. With enough cold air aloft and
overnight minimum temperatures still hovering around the freezing
mark, a light dusting of snow cannot be ruled out early morning
Sunday and Monday for interior portions of the lower Y-K Delta.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 and 2)...
Any lingering gales across the eastern Bering will continue to
diminish through the overnight hours as the low responsible
continues to slowly drift north and weaken. The other story is a
warm front moving closer to the western Aleutians. This front will
produce widespread rain and a few wind gusts from Adak west
through Sunday before moving south with the parent low.

Between the two systems, conditions will remain rather quiet.
Northwesterly flow advecting some colder air through the Bering
will help to produce a few scattered rain and snow showers
throughout the weekend from Dutch Harbor across the Alaska
Peninsula.

&&

.LONG TERM FORECAST (Days 3 through 7)...
The upper level pattern will continue to support a cloudy and
showery regime across the southwest mainland through much of next
week as a longwave trough persists over the eastern Bering Sea,
anchored by a closed upper low which is now progged to linger
offshore of the Y-K Delta region through Friday. The extended
outlook for Southcentral AK has trended drier in recent days,
particularly during mid to late next week as upper level ridging
builds over the eastern Gulf and then extends into the interior
from western Canada. The region still looks to remain in southerly
flow on the western periphery of the ridge, so some lingering
cloud cover and occasional shower activity cannot be ruled out
through Friday. Guidance has also continued to trend farther south
with the low passing south of the Aleutians. This would keep the
chain mostly dry through next week as high pressure builds over
the western half of the Bering, with the upper trough maintaining
scattered shower activity over the eastern Bering. A front
associated with the North Pacific low is still expected to move
north and impact the Akpen with steadier rain and some gusty winds
in the Wednesday/Thursday time frame, possibly spreading to the
southwest mainland by Thursday as details start to become more
uncertain.

&&

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

&&

SYNOPSIS AND MODEL DISCUSSION...DEK
SOUTHCENTRAL ALASKA...PEPE
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...TM
LONG TERM...CB