FXAK68 PAFC 191723 CCA
Southcentral and Southwest Alaska Forecast Discussion...CORRECTED
National Weather Service Anchorage AK
923 AM AKDT Sat Oct 19 2019
.ANALYSIS AND UPPER LEVELS...
A large upper level low remains in place over the Bering and a
second upper level low is centered over the Gulf. At the surface
level, a weakening low just northwest of the Pribilofs continues
to bring in colder air over the western Bering. Meanwhile, a weak
low has spun up over Unalaska Island, bringing cloudy skies and
rain to the eastern Aleutians, which will eventually lift to the
northeast and spread in over the Alaska Peninsula.
The low in the Gulf is centered just southeast of Middleton Island
and is moving southwest. Gusty easterly winds persist along the
northern Gulf coast this morning and showers are evident on radar
imagery over Prince William Sound.
Models remain in good agreement through the weekend. By Sunday
night, models show a few different solutions for the location of
a low lifting over the eastern Aleutians/southern AKPEN. There are
also differences in the position of another low entering the
western Gulf on Monday. There is average confidence in the
forecast and the NAM solution was preferred for the morning
PANC...VFR conditions and light winds will persist. Slight chance
of MVFR ceilings with showers in the vicinity.
.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (through Sunday night)...
A series of weak upper waves lift north across Southcentral
through the the weekend. The first of the waves moves north
across the Cook Inlet Region this afternoon and into the interior
tonight. Mid to upper level flow becomes more southerly bringing
some light overrunning snow to the northern Susitna Valley and
Talkeetna Mountains. Lower elevations to the south will see some
rain showers or pockets of light rain. Precipitation diminishes
inland tonight after the trough passage. However, continued east
flow over the eastern Kenai Peninsula will continue rain in that
region. On Sunday, precipitation increases across the Kenai
Peninsula as a weak surface low moves to the western Gulf south of
the Kenai Peninsula. Also, chances of showers are expected
inland. Weak gap winds are expected across Turnagain Arm and Portage
Valley through Sunday. A weak Matanuska wind develops Sunday evening.
.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 through 3: Today
Partly to mostly sunny skies are expected through this afternoon
under a weak ridge. Clouds will increase this evening, with
showers developing along coastal areas and flurries or light snow
developing over interior areas by early Sunday morning ahead of a
weakening cold front. Any snow accumulation will be minimal.
Partial clearing is possible Sunday afternoon behind the front.
Mostly cloudy skies will return Monday with possible onshore
showers or flurries as a low stalls near the Pribilofs.
.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 through 3:
Today through Monday)...
A stalled upper level low in the Bering will continue to bring
persistent showers to the Aleutians and Pribilofs as its
associated surface lows rotate around it. The heaviest of these
are expected east of and including Unalaska on Sunday as a
relatively stronger meso-low tracks over that area.
.MARINE (Days 3 through 5)...
Beginning the extended marine weather forecast Sunday afternoon,
there will be a broad low pressure centered over the central
Bering Sea with a region of enhanced (25-30 knot) northerly winds
on the backside of the low over the western Bering Sea. There is
high confidence a second low will move into the eastern Bering and
Bristol Bay on Sun night and Mon, bringing with it 20-30 knot
winds and seas 5-9 feet as it stalls in the vicinity of the
Pribilof Islands. There will be quieter winds and seas over the
Gulf of Alaska Sun and Mon as weakening fronts move into the Gulf,
but stronger storms stay well to the south.
Attention quickly turns to a potentially rapidly developing low
late Tue night and Wednesday. There is much higher uncertainty and
lower confidence with the track and strength of this low, with
the GFS favoring a much stronger and powerful westward track of
this low through Bristol Bay, potentially as strong as 960 mb with
storm force winds and high seas through Wednesday. The ECMWF and
Canadian are much weaker and favor a track into the Gulf of Alaska
and Kodiak, with much lower winds and seas over the Bering Sea.
For now a middle ground forecast was favored with a gale force low
projected to track over the AKPEN and Kodiak, but not as far west
as the very strong GFS and not as weak and far east as the weak
Canadian solution which favors the far northeast Gulf of Alaska.
Mariners should beware of this potential storm, with another
couple days of some uncertainty as this low develops.
.LONG TERM FORECAST (Days 3 through 7; Monday through
Beginning the extended forecast on Sunday evening, there will be a
large trough over the Bering Sea, and weak upper ridging over
Southcentral and the ALCAN, stretching west across the Alaska
Range. As the state moves into the early part of next week, weak
embedded waves rotating around the trough will push moisture into
Southwest Alaska, increasing rain and snow threats through
Tuesday. However, Southcentral will likely remain drier as the
precipitation remains mainly along the coast.
Attention then turns to a potentially rapidly developing low in
the north Pacific Tuesday and Tuesday night which may bring the
next chance for significant weather for southern Alaska.
Numerical models indicate significant strengthening is possible with
this low potentially approaching 960 mb Wednesday morning
(potential storm force winds) as it moves into the waters of
Southern Alaska. However, model uncertainty is rather high with
this storm with some models showing a track over Bristol Bay with
others favoring an eastward track across the North Gulf. These
track differences result in a lot of uncertainty regarding
sensible weather across Southern mainland, with some solutions
(the ECMWF, specifically) favoring a potential snow event for
parts of Southcentral while the GFS favors a significant wind and
warm-rain event.Either way, expect the possibility of strong
winds and high seas in the coastal waters as well as the potential for
heavy coastal precipitation. In addition, expect the possibility
of gusty northwest gap winds along the Alaska Peninsula to last
through Friday. Another low moves into the western Bering Friday
morning into Friday evening as the storm track shifts west.
PUBLIC...Flood Watch 121.
SYNOPSIS AND MODEL DISCUSSION...KO
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...AP