Area Forecast Discussion
Issued by NWS Anchorage, AK
FXAK68 PAFC 231302
Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
502 AM AKDT MON MAY 23 2016
.ANALYSIS AND UPPER LEVELS...
A zonal pattern is present over the area with a couple of
shortwaves moving through. The first is pushing through the
Southcentral from the west and bringing light rain to the area.
The second is over the Central Bering and is also producing rain
as it moves east. In between the two shortwaves, weak ridging
is moving in over southwest Alaska.
The models are in good agreement through the mid term with the
exception of the low approaching the Western Aleutians Tuesday.
The GEM and EC keep a more northern track than do the GFS and NAM.
The more southern track of the GFS and NAM was preferred.
.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 and 2)..
Rain continues to develop along a weak frontal boundary through
the morning from the Talkeetna Mountains south toward the eastern
Kenai and Western Prince William Sound. The boundary will shift
slowly east by this afternoon keeping most of the rain activity
along the northeast Gulf coast and the higher terrain of the
Copper River Valley. A thermal trough across the Yukon extends
across the eastern Alaska Range in the afternoon bringing a focus
for heavier shower activity. Thunderstorms are not expected to
develop as cloud cover should limit instability; however, an
isolated strike or two cannot be ruled out as the upper low pushes
a strong shortwave across the eastern range late this afternoon
and early evening.
Most areas behind the upper low will experience breaks in the
clouds this afternoon and late evening as transient ridging aloft
moves in from the west. At the surface...weak low pressure
becomes stationary along the northeast Gulf tonight as a ridge
builds across the southwest mainland. This regime sets up offshore
flow across the southern mainland with gusty conditions expected
along channeled terrain. Another upper wave moves in from the
southwest at a fast pace without an associated surface
front...therefore only light showers are expected into Tuesday
morning with a greater chance to see accumulations across the
eastern Alaska Range as the thermal trough remains along the
.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 and 2)...
One more good shot of rainfall is expected across Southwest Alaska
during the day today as an upper level trough swings through the
region. Rainfall should quickly taper off from west to east with
this quick moving trough with most locations seeing an end of
rainfall by midnight tonight. Weak surface high pressure will
begin to build across the Bristol Bay area late this morning and
continue to build across the Y-K Delta and Kuskokwim Valley by
Tuesday afternoon. This high pressure will help keep the weather
on the dry side through Wednesday after nearly a week of on and
off rainfall. The high pressure overall is rather unimpressive
which will allow some rainfall associated with weak shortwaves
traversing the zonal flow over the Bering Sea to return to the
Kuskokwim Delta and Kuskokwim Valley Wednesday night into
Temperatures have been slower to warm up than expected because a
tap into the arctic air mass over the Beaufort and Chukchi Seas
continues. This feed of cooler air should get cut off Tuesday
afternoon which will allow temperatures to warm back to near
normal temperatures by Wednesday.
.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 and 2)...
Zonal flow will continue across the Bering Sea through Tuesday
afternoon before a deepening upper level low moves near Shemya.
Rain chances through Tuesday morning will be largely suppressed by
weak high pressure building across the region from the North
Pacific. This high pressure will act as a double-edged sword as it
should allow some pretty nice fog development with subsidence
keeping moisture trapped at the lowest levels of the atmosphere.
An approaching upper level and surface low on Tuesday will help
displace this fog as mixing will become more readily available
with the departure of the high pressure system.
Models have been in pretty solid agreement in both timing and
location of the low near Shemya Tuesday morning which leads to
high confidence that gale force winds will be seen across the
western Aleutians on Tuesday and a few gale force gusts could be
seen over the central Aleutians on Wednesday. Based on the PASY
RAOB and forecast soundings, it appears an unseasonably moist air
mass will be advected into the Bering Sea which will help bring
heavy rain to the Western and Central Aleutians on Tuesday and
.LONG TERM FORECAST (Days 3 through 7)...
The Southcentral mainland, and the southwest Alaska regions will
have drier conditions as high pressure builds into the region by
Tuesday afternoon through Thursday morning. While the northern
Gulf of Alaska will have a weak low by Tuesday resulting in
moisture along the coastal communities before tracking to the
lower southwestern Gulf by Thursday. Then an upper level shortwave
drops down from the north, and tracks along the Alaska Range
before a secondary shortwave digs farther south into the base of
the trough over the Southwest Alaska region by Thursday morning.
This synoptic feature will develop into a closed low along the
Alaska Peninsula by Saturday. Therefore, the southwest Alaska
region, Gulf of Alaska, and the northern coastal communities will
see slightly cooler temperatures with increased cloud cover going
into next weekend. On the Bering Sea side, they will be under the
influence of an amplified ridge of high pressure heading into the
midweek. This synoptic feature will gradually move eastward before
developing into a strong closed high pressure over the eastern
Aleutians by Thursday. This upper level closed high will further
strengthen, extend through the western Bering Sea into the eastern
Siberian region heading into next weekend. Look for marine layer
stratus and fog to develop throughout next week for the Bering
Sea and the Aleutians. This high pressure will keep systems out
of the Bering Sea except for the western Aleutians being affected
slightly as systems track by into the northern Pacific Ocean. The
forecast confidence remains average as the models have become
better aligned for next week.
SYNOPSIS AND MODEL DISCUSSION...dk
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...mc