Area Forecast Discussion
Issued by NWS Anchorage, AK
FXAK68 PAFC 241157
Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
357 AM AKDT Fri Mar 24 2017
.ANALYSIS AND UPPER LEVELS...
Dominant high pressure has maintained over the eastern Bering and
is continuing to bring clear skies to southwest Alaska and western
parts of Southcentral Alaska. The main trough sits over eastern
portions of Southcentral Alaska and has brought some light snow
to some of these areas. West of the ridge, a front is starting to
move in over the Western and Central Aleutians bringing rain and
gale force winds to the islands.
For the most part the models are in good agreement through the mid
term. However, there are some differences with a low moving to
south of the Eastern Aleutians on Sunday. The EC brings the low
the furthest north and then has it absorbed into the low further
to the west. The other models keep the low tracking east out ahead
of the westerly low for a while longer before stalling it and
having it absorbed. Except for the GEM which always keeps it
PANC...VFR conditions and light winds will persist.
.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 and 2)...
The surface pressure gradients will increase across Southcentral
tonight as the trough over the Gulf intensifies some. As a result,
outflow winds across the North Gulf Coast (Valdez/Thompson
Pass/Copper River Delta), eastern Kenai Peninsula, and the
Matanuska Valley will increase this evening and hold into Saturday
morning. Winds will then decrease Saturday afternoon and evening
as pressure gradients relax. The proximity of the upper trough
will continue the threat of snow showers over the northern Gulf
and portions of the Copper River Basin into Saturday. Snow showers
will likely become more widespread across the northern Gulf coast
on Saturday/Saturday night as upper trough overhead strengthens.
.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 and 2)...
Crystal clear skies remain the norm once again as a strong area of
high pressure centered near the Bering Strait retains full control
of the weather. The continuation of the broken record pattern
means more sunshine and seasonable temperatures during the day and
cool temperatures at night. Most areas are forecast to remain
above 0 though thanks to steady northeast winds. Thus, while the
winds will keep nighttime lows from dropping as far as they could,
the resultant wind chills will definitely remind those venturing outside
that Old Man Winter isn`t going out without a fight. For the next
several nights, wind chills in most areas are aiming for a few
degrees on either side of 10 below. However, twelve and a half
hours of daylight (and counting) will still make for healthy
temperature recoveries well into the 20s during the day under
mostly sunny skies.
.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 and 2)...
A gale force front is pushing across the western and central
Aleutians and is the cause of the most active weather in all of
Alaska this morning. The front is wrapped around the northeast
side of a low that is nearing its peak intensity as it approaches
the Aleutians. The front will already begin weakening later this
afternoon into tonight as the parent low weakens and halts its
approach to the western Aleutians. Showery conditions with gusty
southeast winds will remain the norm right through the weekend as
the pattern remains warm and wet, but total precipitation amounts
will be light. By Sunday, another low will advance any heavier
precipitation further east into the eastern Aleutians, but a very
stubborn high pressure system over the northern Bering will
curtail significant northward progress for any areas of
precipitation and associated low pressure systems.
.LONG TERM FORECAST (Days 3 through 7)...
The ridging over the Bering Sea continues through Saturday before
an upstream North Pacific low pressure system pushes the ridge
into the Gulf of Alaska by Monday. Meanwhile, an upper level
closed low will be positioned over the Anchorage Bowl with an
associated trough extending into the Gulf from Saturday through
Tuesday, before merging with several weak North Pacific Lows.
The next major storm force low tracks towards the Eastern
Aleutians by Thursday morning, with an associated weather front
entering the Gulf. This brings a pattern change with the offshore
flow over the Southcentral region diminishing, and shifting to
onshore southerly flow. There is uncertainty with timing of how
long the arctic trough stalls over the Southcentral region. The
GFS model is showing a faster solution, and the ECMWF was slower
with this synoptic feature. Meanwhile, by Thursday the jet stream
transitions to a southwesterly flow just south of the Eastern
Aleutians extending eastward into the lower southeastern Gulf.
This enhances storm tracks from the North Pacific area into the
Eastern Aleutians/Gulf region. The forecast confidence is low as
we head into midweek and beyond due to the uncertainty with the
timing/strength with the upcoming low pressure systems as they
track towards the Southwest/Southcentral regions.
MARINE...Gales...172 173 174 175 176 177 178.
Heavy Freezing Spray...121 185.
SYNOPSIS AND MODEL DISCUSSION...DK
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...JW