FXAK68 PAFC 271241
Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
441 AM AKDT FRI MAY 27 2016
.ANALYSIS AND UPPER LEVELS...
A low centered 240 nm north of Shemya is currently impacting much
of the western and central Bering, bringing areas of light rain
and gusty winds. Meanwhile, a mid-level ridge centered over the
Yukon-Kuskokwim Delta region continues to push slowly northward
across the western Alaska Mainland. Offshore flow has allowed for
mostly clear skies at almost all southern Alaska mainland
Models remain in fairly good agreement in the short term as they
continue to lock onto one general solution as the mid-level high/ridge
pushes northward to the far northwest mainland. Models become
more uncertain towards Sunday as a stout 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/thunderstorm development in Southcentral on Sunday.
Additionally, the development of a northeasterly jet between the
high over the northwest mainland and the disturbance over the
southeast mainland will induce a northeasterly jet which may help
to bring even warmer and drier conditions to parts of the
southwest mainland Sunday.
.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 and 2)..
An upper level ridge continues to build across Southcentral
Alaska today and Saturday bringing very warm temperatures and dry
conditions across much of the area. Afternoon temperatures are
expected to rise into the 70s inland with cooler conditions along
the coast with sea breezes through Saturday. On Sunday and Sunday
night, the upper high slips a little north allowing a
west/southwest moving trough out of Canada to push across the
Copper River Basin/North Gulf Coast by afternoon. This feature will
bring increased cloud cover as well as chances of showers and
thunderstorms to the Copper River Basin Sunday afternoon. Clouds
and shower potential will likely spread west to the remainder of
Southcentral during the evening and overnight hours Sunday. This
trough will also bring slightly cooler temperatures to the Copper
River Basin Sunday.
Warm and dry Conditions are expected across much of Southcentral
Alaska through Sunday, though a trough moving in from the West
Sunday afternoon will bring slightly cooler temperatures and
higher RH values to the Copper River Basin. Until then,
temperatures are expected in the 70s accompanied by RH values
dipping into the 20s inland during the afternoon hours today and
Saturday. Winds during the afternoon hours should be fairly light
in areas approaching critical temperature and RH values. Afternoon
sea breezes will keeps the coasts cooler and moist.
.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 and 2)...
High pressure will continue to build over the area today, bringing
clearing skies and warming temperatures to the southwest Mainland
through this weekend. This will provide a strong enough cap to
limit any convective showers from developing through Sunday over
the area. Otherwise temperatures will remain seasonable, and
conditions over the interior will continue to dry through Sunday
with increasing offshore flow.
RH Values over much of the Southwest Mainland will continue to
decrease over the weekend, as high pressure over the area keeps
clear and warm conditions in the forecast. The high will push
further north on Sunday as a wave tracks into the area from the
east, developing a northeasterly jet ahead of the wave over the
southwest interior. RH values may drop below 25 percent over the
Middle Kuskokwim Valley and inland areas of the Kuskokwim Delta
on Sunday, coinciding with high temperatures in the mid 70s and
15-25 mph northeasterly flow. With these parameters, a Fire
Weather Watch is strongly being considered for these areas.
.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 and 2)...
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 keep winds below gale force though Saturday throughout much
of the region, with only a chance for showers and patchy fog.
Farther west, a series of fronts will bring rain and gusty winds
to the Western and Central Aleutians as they track through the
area over the weekend.
.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 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...CC
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...TP