Area Forecast Discussion
Issued by NWS Anchorage, AK

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000
FXAK68 PAFC 081247
AFDAFC

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
447 AM AKDT Sat Aug 8 2020

.ANALYSIS AND UPPER LEVELS...

A 1006 mb elongated surface low is sitting just west of Middleton
Island with a trough extending eastward from it. This system is
producing some scattered showers for portions of Prince William
Sound and the northern Gulf as it continues to weaken and lift
north this morning. To the north, a weak upper-level wave over
interior Southcentral is also moving north toward the Alaska Range
in response to the the cyclonic flow around a deeper upper-level
trough over Southwest Alaska. Scattered showers linger early this
morning across the Mat-Su Valleys in response to the increased
instability associated with this feature. Similarly, scattered
showers continue this morning across interior Bristol Bay, aided
by a moist, westerly onshore flow and a weak wave extending
northwest from the upper-level wave over the northern Gulf.

Farther west, there is a shortwave digging across the northern
Bering this morning. This is translating into a surface low moving
out of the Gulf of Anadyr. A warm front associated with this low
can be seen stretched from the center of circulation south and east
to Saint Matthew Island and the Pribilofs this morning on infra-
red and water vapor satellite imagery. A cold front extends south
from the low and is entering the western Bering. For areas of the
eastern Bering southeast to the AKPEN a ridge of high pressure is
holding tight overhead, keeping conditions rather quiet with low
stratus the main weather concern today.

&&

.MODEL DISCUSSION...

Models are coming into better agreement concerning the development
and evolution of a storm-force low moving across the Gulf this
weekend. The 00z NAM was the strongest and most west with the
track, and was seen as the outlier when compared to the other
three (GFS, EC, GEM) which favored a more eastward track. The 06z
NAM has shifted back east and, while still the strongest, is now
more in line with other model solutions. Therefore, there is
increased confidence in the eastward track, and, thus, only minor
edits to the previous forecast package.

&&

.AVIATION...
PANC...VFR conditions with isolated rain showers are expected
through the TAF package. Locally gusty southeast winds are
expected across the airport complex later this afternoon through
the evening.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 and 2)...

A weak upper level low is moving into Southcentral Alaska today
from the west, ahead of a rapidly strengthening low that will
move into the Gulf of Alaska tonight. This upper level wave is
helping to keep the atmosphere unstable enough for some showers
across the area today. The Susitna Valley and interior of the
Kenai Peninsula may be unstable enough for an afternoon or evening
thunderstorm, but development is not expected to be widespread.

By tonight, the focus shifts to the low entering the Gulf. This
low is rather strong for this time of year and is expected to
produce storm-force winds in parts of the Gulf Offshore waters.
Along the north Gulf coast from Montague island eastward, the
winds are currently forecasted to reach 45 kt in the barrier jet
that will develop there. However, there is a chance that storm
force winds could develop in the barrier jet late tonight into
early Sunday morning as at least one of the newest model runs is
increasing the winds around the low a little bit more. This low
will move quickly eastward and weaken some before moving near
Yakutat Sunday night.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 through 3)...

Scattered showers are expected today from interior Bristol Bay to
the Middle Kuskokwim Delta as a shortwave lifts north into
interior Alaska. An isolated thunderstorm is also a possibility
this afternoon and evening along the Alaska Range north of
Iliamna. A transient ridge will then slide over Southwest Alaska
overnight before the next upper-level shortwave slides toward the
west coast late Sunday morning. This feature is associated with a
weak surface low near Nunivak Island with a cold front sliding
east across the eastern Bering. This system will bring scattered
showers to coastal locations from Port Heiden and King Salmon
north to Bethel through Sunday night before the low dissipates
and the upper-level low shears apart, keeping the interior
relatively dry. A secondary trough then digs south along the coast
for Monday. This feature will help to destabilize the atmosphere,
resulting in another round of showers from Bethel and Aniak to
King Salmon and Iliamna through Monday evening.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 through 3)...

A low situated southwest of Saint Matthew Island is pushing a
warm front east this morning over the Pribilofs. A trailing cold
front is draped across the Western Bering. Ahead of this system,
low stratus is lingering over the eastern Bering south to the
AKPEN and eastern Aleutians, trapped underneath a ridge of high
pressure. Widespread rain and southerly winds are occurring along
the warm front and will continue to impact the Pribilofs today,
with the rain transitioning to showers this evening as the cold
front sweeps across the Bering. Rain will slide east with the
system, moving into the eastern Bering and Bristol Bay by Sunday
morning. Rain will again transition to showers along the eastern
Aleutians and AKPEN by Sunday evening as the frontal system
dissipates and the upper-level support shears apart. A ridge will
build in over the western and central Bering in the wake of this
system, but will quickly be pushed east toward the eastern Bering
on Monday as a second frontal system slides east from the western
Aleutians over the southern Bering and eastern half of the Chain.
This front is associated with a surface low that will move just
south of Attu by Sunday afternoon. This system will slow and stall
out over the Rat Islands by late Monday as it becomes vertically
stacked.

&&

.MARINE (Days 3 through 5: Mon through Wed)...

The strong low pressure that was set up across the northern Gulf
coast the previous few days will continue to weaken through
Tuesday. Meanwhile, to the west, models remain in good agreement
with a low positioned near Shemya Monday afternoon, with its
associated front over the central Bering and Aleutians. Models
agree that small craft advisory level winds will accompany this
system, but are in lesser agreement whether or not they will
reach gale force strength during this time. This system weakens as
it shifts eastward, with the front reaching the Southwest coast
by Wednesday. Models start to diverge on Wednesday afternoon as to
whether or not a low forms south of the Aleutians, extending a
front into the Gulf through late Wednesday.

&&

.LONG TERM FORECAST (Days 3 through 7: Tue through Fri)...

A low in the western Bering will keep a showery pattern stretched
across the Pribilofs and Aleutian Chain as this system progresses
eastward. Mainland Alaska remains relatively dry through early
Wednesday with an upper level low parked over the region. The
pattern begins to shift on Wednesday afternoon when the
aforementioned front reaches the Southwest coast, increasing
cloud cover and the chances for widespread rain through the end of
next week. Timing of this system and the placement of the low is
still the biggest model uncertainty. A chance of rain remains in
the forecast for Southcentral Alaska with the uncertainty in the
track of this system for the end of next week.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...Gale 119 120 131 132.
FIRE WEATHER...NONE.

&&
$$

SYNOPSIS AND MODEL DISCUSSION...TM
SOUTHCENTRAL ALASKA...EZ
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...TM
MARINE/LONG TERM...AH


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