Small Craft Advisory 678, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
543 AM AKDT Sun Sep 2 2018

.ANALYSIS AND UPPER LEVELS...
A strong upper level ridge remains centered over the Bering while
a frontal system associated with a Kamchatka low approaches the
western Aleutians. An upper level trough stretches from a low over
the southern half of the Southeast Alaska Panhandle back to the
west across the southern Gulf and over the Alaska Peninsula to the
eastern Aleutians. Over southern mainland Alaska, dry
northwesterly flow prevails, although a shortwave trough swinging
through interior Alaska north of the Alaska range is bringing some
clouds and the potential for isolated mountain showers to northern
portions of the Copper River Basin.

&&

.MODEL DISCUSSION...
With the relatively quiet weather pattern continuing, models
remain in good agreement through midweek

&&

.AVIATION...
PANC...Winds at PANC will remain fairly light under the persisting
northwesterly flow aloft. With a building ridge continuing to
stabilize conditions there is a chance of some shallow patchy fog
forming during the early morning hours however otherwise VFR
conditions will prevail.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 and 2)...
A dominant upper level ridge sitting to the west will continue to
provide for dry conditions across most of Southcentral and the
Gulf for the next couple days and beyond. The only chance of
precipitation will be the northern to eastern Copper River Basin,
where a few showers are possible today and tonight as an upper
level short-wave passes through. There may be some occasional mid
to high clouds transiting the region as short-waves drop down the
east side of the ridge, but mostly clear skies will be the norm.
Generally expect light winds with the exception of some locally
gusty winds along the coast, namely for Seward/Resurrection Bay
and Whittier/Passage Canal. Clear skies will lead to potential for
shallow ground fog each night, but in the absence of a stronger
subsidence inversion, it looks like any fog that does form will be
localized in nature and burn off pretty quickly as the sun rises.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 and 2)...
A dome of high pressure has moved into the Bering and continues to
push eastward towards Southwest Alaska. With widespread subsidence
in place, expect the warming and the drying trend to continue.
The main forecast challenge will be determining which areas will
get fog over Southwest Alaska the next two mornings. The mild
weather will continue through Thursday for Southwest Alaska.

&&

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

A ridge over the western Bering will migrate to the eastern
waters through Tuesday. This ridge will continue to steer warmer
temperatures aloft into the region resulting in more fog and
stratus. The next front remains on track to enter the western
Aleutians late Sunday night. This low will already be in the
process of decay when it moves into the chain. Expecting a wave of
precipitation and gusty winds.

&&

.LONG TERM FORECAST (Days 4 through 7: Wednesday through
Saturday)...

Models are all in good agreement for the long term forecast
depicting a high amplitude blocking ridge continuing to dominate
the upper level pattern. The ridge axis is expected to remain over
the western coast/eastern Bering, which will bring dry offshore
flow to most of the southern mainland and extend the streak of
unusually nice late summer/early fall weather to the area.

One kink to the forecast comes in on Thursday as models are
showing a short wave trough dropping south out of the Arctic.
There are differences in how far west the trough digs which will
impact how much and where precipitation will fall. The
EC/Canadian all show the trough digging across the western half of
southern Alaska which would sweep a cold front across the area
with rain extending across the AKPEN east through the Copper River
Basin. The GFS shows a weaker trough that only pushes across the
eastern half of the state, bringing light rain to the Copper River
Basin while locations west remain dry.

Regardless, there is good agreement that as the trough slips into
the Gulf of Alaska and merges with a large upper low over the NE
Pacific, the large blocking high will reamplify and bring
continued dry and sunny weather to the southern mainland through
at least next weekend.

&&

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

&&

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