Small Craft Advisory 380, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
440 AM AKDT Thu May 11 2017

.ANALYSIS AND UPPER LEVELS...
Ridging has moved in over western Alaska keeping skies clear and
winds calm for southwest Alaska. Southcentral Alaska is not as
much under the influence of the ridging and saw more afternoon
convection including thunderstorms on Wednesday, but things have
calmed down overnight. Behind the ridging, a low near the Western
Aleutians is swinging its front across the Pribilof Islands and
Eastern Aleutians as it follows behind the ridge.

&&

.MODEL DISCUSSION...
For the most part the models are in decent agreement with the main
synoptic features. However, they have been struggling with the
low that is moving into the southern Bering. They have been
inconsistent with its placement from run to run and compared to
other guidance. But these differences look to have little impact
as all models are relatively close with the progression of the
associated front.

&&

.AVIATION...
PANC...VFR conditions persist. Winds should remain relatively
light with afternoon and evening sea breezes.

&&

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

Unstable conditions will persist across much of Southcentral
through Friday. The mountains will be the main focal point for
afternoon and evening shower development. Stability indices would
once again support isolated wet thunderstorms with the most
likely areas along the Talkeetna mountains and the Copper River
Basin. The north to east steering flow aloft today would tend to
carry the showers across the Anchorage Bowl and isolated wet
thunderstorms over the Copper River Basin and the MAT-SU valleys
in the vicinity of the Talkeetna Mountains. The flow aloft becomes
more southwesterly on Friday, so any shower/isolated thunderstorm
activity will be along the Chugach and Talkeetna mountains and in
general across the Copper River Basin. A weather front brings
cool and wet conditions to Kodiak island tonight and Friday.

Expect warm temperatures across inland areas through Friday with
numerous locations likely to reach the low to mid 60s.

&&

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

High pressure over Southwest Alaska today will usher in what
should be the warmest day of the year so far. With sinking air
drying at all levels, cloud cover this afternoon will be sparse,
and with warmer air advecting in, temperatures will easily climb
well into the 60s, approaching 70 in some places in the Lower
Kuskokwim Valley. The sunny and dry conditions will feature
relative humidity values falling to anywhere from 15 to 25 percent
at inland locations. The high pressure system overhead will also
mean most areas will see light and variable winds. Along the
coast, the next front is making its way towards the area. The
later in the afternoon it gets, the more likely there will be more
cloud cover. Tonight, rain will begin overspreading the area, but
as it is associated with a slowing, dying front, it is unlikely to
progress very far inland, so the Lower Kuskokwim Valley will
remain dry through the day Friday. By Friday night, the parent low
will push into Southwest Alaska bringing chances of rain to all
areas.

&&

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

A strong low over the western and central Aleutians is near peak
intensity this morning. As it begins to weaken, the low will also
take on an easterly movement, traversing the Bering and passing
north of the Pribilofs Friday evening, before heading into the
Kuskokwim Delta area on Saturday. For today, the western and
central Aleutians along with the adjacent coastal waters will see
gale force winds, heavy rain, and 20 foot seas. The associated
front has already pushed into the Pribilofs, bringing locally high
wind gusts and rain to the area. The front will continue moving
eastward through the eastern Bering today.

&&

.LONG TERM FORECAST (Days 3 through 7)...

Beginning the extended period forecast Friday evening, a closed
low will be in the process of moving from the Eastern Bering Sea
into Southwest Alaska. The numerical models have not handled this
system well the past three days, but there is now high confidence
in a track from Southwest Alaska into the North Gulf by Saturday
night. This low will be occluded, so there will not be much of a
moisture tap associated with it, but it will spread light rain
into all of Southwest Saturday before moving east. While the low
will be digging into the Gulf Saturday night into Sunday, enough
cyclonic flow aloft (DCVA) will help support organized
rain/showers across Southcentral before the low moves south by
Monday morning. Thereafter, weak upper flow over Southern Alaska
will bring drying conditions, although afternoon diurnal showers
will remain a threat.

Farther west, a broad and slow moving upper low will form
southwest of Shemya Friday night with the associated front moving
north toward the Aleutian Chain. This front will slowly move east
through Tuesday, bringing widespread light rain to that area
before lifting north toward Southern Alaska Tuesday and Wednesday.
This front looks rather weak, at this juncture, and will not have
much upper support with it, but this will increase clouds and
precipitation chances to Southern Alaska after a brief dry period
Monday. The front falls apart Thursday, leaving shower activity
and cloudiness across the southern mainland.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...Gales...174 175 176 177 185.
FIRE WEATHER...NONE.

&&

SYNOPSIS AND MODEL DISCUSSION...DK
SOUTHCENTRAL ALASKA...BC
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...JW
LONG TERM...JA