Area Forecast Discussion
Issued by NWS Anchorage, AK
FXAK68 PAFC 270021
Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
421 PM AKDT THU MAY 26 2016
.ANALYSIS AND UPPER LEVELS...
A low centered just north of Shemya is currently impacting much
of the western and central Bering, bringing widespread light rain
and gusty winds. Meanwhile, an upper level ridge continues to push
eastward into the Alaska Mainland. Beneath this ridge a broad
stratus deck covered the Bering and portions of the Southwest
mainland this morning. However, this afternoon offshore flow is
starting to become established across much of the southwest and as
a result much of the stratus deck is breaking up into sunny skies.
Models remain in fairly good agreement in the short term as they
continue to lock onto one general solution as the upper level
ridge pushes northward into the alaska mainland. Models become
more uncertain towards Sunday as an upper level wave pushes
westward into the eastern portion of Southcentral. As a result,
there is some uncertainty in the timing, intensity and/or
location of shower development in Southcentral on Sunday.
.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 and 2)..
An amplifying upper level ridge axis is building into
Southcentral, and will continue to build into the state through
Saturday. This will allow for warming temperatures and decreasing
cloud cover along with drier conditions. A weak northerly offshore
flow will also result in breezy northerly winds tonight through
Saturday, strongest toward the Alaska Range and into the Copper
Basin. Sea breezes will come in during the later afternoons along
the coast, moderating temperatures somewhat, but it will still be
above average region wide.
.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 through 3)...
There remains very good confidence that ridging building into the
area will bring clearing skies and warming temperatures to the
southwest Mainland into this weekend. This will provide a strong
enough cap to prevent any convective showers from developing
through Saturday, even along the mountains. Otherwise
temperatures will remain seasonable with relatively weak offshore
.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 through 3)...
Much of the Bering Sea will move into a quieter pattern into this
weekend as a weakening low over the western Bering moves towards
eastern Siberia and is replaced with weak high pressure. This will
leave keep winds below gale force though Saturday throughout the
region, with only a chance for showers and patchy fog.
.LONG TERM FORECAST (Days 3 through 7)...
On Day 3, models have come into slightly better agreement with
the handling of the low over the far Western Aleutians Islands
with the models generally converging on a forecast pressure in the
mid to upper 970 mb range but with a wide spread in actual
position. Most models are clustering the low further to the west
near Shemya with the EC developing the low and moving it further
eastward near 180. The 12Z EC appears to be an outlier, thus the
Day 3 forecast for the Western domain uses an average position
south-southeast of Shemya with a low-end Gale force front moving
into the Western Aleutians on Day 3 into Day 4.
Over mainland Alaska for Day 3, most of the area will generally
see warm and dry conditions. Isolated showers are expected along
the Aleutian Range in the Southwest and over much of the Copper
River Basin. The ridge currently over Southwest Alaska today will
migrate northeastward with its center over the Seward Peninsula,
thus putting most of Southern Alaska in northeasterly flow.
Simultaneously, an upper level wave is expected to moves southward
over the Copper River Basin and southward into the Gulf side of
the Kenai Peninsula. This wave will have some 850-500 mb moisture,
so isolated showers are possible over the area. The atmosphere
over the region is expected to be somewhat unstable with LI values
of 0 to -2 and CAPE values in the 200-400 J/kg range, the chance
for some very isolated thunderstorms are possible over the Copper
River Basin and portions of the Kenai Peninsula Sunday afternoon.
This will bear watching in further forecast packages for travelers
through the Copper River Basin and with an increase in outdoor
recreation over the Memorial Day weekend.
Over Southwest Alaska, while CAPE and LI values appear to
be conductive for thunderstorms over portions of the Bristol Bay
region on Sunday, there is a lack of upper level support, thus at
this time thunderstorms seem unlikely.
For the remainder of the forecast, models diverge even further
with the North American models generally showing a similar
solution and the 12Z EC remaining the outlier. The extended
forecast went heavy to the WPC forecast, which as usual was a
blend of EC/NAEFS ensembles. In general, expect warm conditions
through the extended with rainfall mainly limited to the Pacific
and Gulf of Alaska coasts.
SYNOPSIS AND MODEL DISCUSSION...en
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...dek