Area Forecast Discussion
Issued by NWS Anchorage, AK

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412
FXAK68 PAFC 081643 CCA
AFDAFC

Southcentral and Southwest Alaska Forecast Discussion...CORRECTED
National Weather Service Anchorage AK
743 AM AKST Sun Dec 8 2019

.ANALYSIS AND UPPER LEVELS...

A high amplitude pattern remains in place with a strong upper
level ridge parked over the Alaska Panhandle while an upper level
low has moved to the northern Bering. A front currently lifting
inland over Southcentral this morning continues to drive warm,
southerly flow over the southern half of the state with
temperatures reaching as warm as 58 degrees in Seldovia late
Saturday evening. Accompanying these warmer temperatures, gusty
southeasterly winds have picked up during the overnight hours as
the front continues to move inland. Meanwhile out west, cold
northerly flow on the backside of the low in the northern Bering
persists this morning.

&&

.MODEL DISCUSSION...

Model solutions are in good agreement regarding the current front
lifting inland over Southcentral. There is overall better
agreement with the next low arriving from the North Pacific late
Sunday into early Monday. As this low moves over the AKPEN, there is
less certainty on the exact track it takes once it arrives in the
Bering, and also how much the low strengthens as it travels
northward along the Southwest coast. However, given the consistency
models have shown with the continued trend of the low strengthening
as it lifts northward, we are still confident that the impacts
(strong winds/heavy precip) will remain relatively the same.

&&

.AVIATION...
PANC...A frontal boundary has pushed in overnight bringing gusty
southerly flow to the terminal that will persist through midday.
Wind shear will become a concern again this evening as another
front approaches the area. Expect northerly flow at the terminal
with southeasterly flow aloft.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 and 2)...
A brief break in the weather is expected today as the weather
system over the area last night moves north of the area. A
powerful north Pacific low will move into the Gulf today and then
into Southcentral tonight. This will bring strong winds across
the Gulf through Monday with Storm warnings over many of the
marine areas. This will also bring very strong winds to Turnagain
Arm and the higher elevations around Anchorage. This system is
also loaded with moisture and is quite warm. Heavy precipitation
is expected along and near the Gulf coast. Rain is the expected
precipitation type over most lowland areas with temperatures in
the 40s on Monday. The exception to this will be the northern
Susitna Valley and the Copper River Basin, where there may be a
mixture of rain and snow, but chances of precipitation are low.

&&

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

Active weather will continue to be seen across Southwest Alaska
over the next few days. Strong winds continue across the Kuskokwim
Delta Coast as one low exits to the north this morning, giving a
quick break in weather across the remainder of Southwest. The
pattern quickly shifts this afternoon as a powerful and fast
moving North Pacific low moves into the region. This low will
bring snow, which eventually transitions to rain, as it lifts
across the greater Bristol Bay area this evening into the morning
hours Monday. Strong east to southeast winds will bring gusts to
60+ mph for areas in Bristol Bay and along the Alaska Range later
today into the morning hours of Monday as the front lifts northward.

As this feature continues a northward track over the Kuskokwim
Delta, there will be the potential for blowing snow ahead of this
warm front overnight into Monday morning with sustained winds of
35+ mph. A Winter Weather Advisory remains in effect for the
Kuskokwim Delta Coast as a brief period of heavy snowfall, along
with potential blowing snow, could reduce the visibility across
the areas. By Tuesday morning, the pattern shifts back to a
quieter one with winds decreasing and precipitation beginning to
taper off.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 and 2)...

As a gale force low continues moving into the northern Bering
through this afternoon, northerly flow moves into the western
Bering and Aleutians. Meanwhile, a fast moving North Pacific low
brings gale force winds into Bristol Bay and the eastern Bering by
this afternoon, with the low center strengthening as it crosses over
the Aleutians into the eastern Bering by Monday morning. This low
will continue to deepen to an impressive 955-960 mb by Monday
afternoon.

Models still have some disagreement of the position and strength
of this low, which will continue to be looked at as the low moves
into the area. There is good agreement that there will be a small
swath of storm force winds south of the Alaska Peninsula this
afternoon as the low first approaches our area. However, once the
low moves into the eastern Bering, it is less certain on strength
of winds over Bristol Bay. The GFS solution has storm force
northeasterly winds for Monday morning, while the NAM continues to
be the weaker solution with sustained winds 10 to 15 knots weaker
during this time.

&&

.MARINE (Days 3 through 5)...

...Bering Sea and Aleutian Coastal Waters...

An area of low pressure near Nunivak Island early Tuesday morning
will bring high sustained gale force winds to the eastern Bering
Sea and Bristol Bay region, with perhaps some low-end storm force
winds just offshore from the Kuskokwim Delta. This low will then
retrograde (move west) and slowly weaken as it reaches Saint
Matthew Island by evening, with the winds having subsided to less
than 30 knots by then. For the remainder of the region, winds and
waves will generally be less than 25 knots with waves generally
less than 15 feet. This will continue into Wednesday and Thursday
for all of the forecast area.

...Gulf of Alaska...

Sustained storm force winds ahead of a surface front will plague
the northern Gulf early Tuesday morning. A favorable dynamic fetch
ahead of this feature will allow seas to build into the 25 to 30
foot range. These winds will rapidly drop to the small craft variety
by the afternoon, as the best dynamics associated with the front
push inland. The wave heights will also drop due to the decrease in
wind energy.

This reprieve will be short-lived though, as yet another front,
associated with a north Pacific low, moves into the region late
Tuesday night/Wednesday morning. Sustained winds will increase to
gale force, with the long fetch allowing waves to once again
increase into the 20 to 25 foot range.

Heading into Thursday, both the waves and winds will subside as a
weakening area of low pressure enters the southwestern Gulf.

&&

.LONG TERM FORECAST (Days 3 through 7)...

The forecast remains fraught with uncertainty due to model
discrepancy, but some items remain consistent. Synoptically, a
progressive pattern will persist over the Bering and Alaska.
Starting Tuesday, a vertically stacked low will drift into the
northern Bering, steering modified Arctic air over the Aleutians
and Bering. The low will gradually weaken and shift towards
Siberia, but in the meantime expect scattered showers over much of
the Bering/Aleutians through Thursday. Meanwhile, a north Pacific
low will drift northward and push a warm occluded front toward
the southern Mainland. Models are consistent with bringing decent
precipitation to the AKPEN/eastern Aleutians, but how far north
and east precipitation reaches is tough to discern, given the lack
of consistency with track of the steering low and potential for a
triple-point low to develop. Right now it looks likely that the
northern Gulf Coast will see precipitation as a front pushes
north in the Wednesday to Friday timeframe. By Friday, a strong
low will approach the western Aleutians and bring a good swath of
precipitation and gusty winds. The front will quickly traverse the
Chain Friday, possibly turning the Southwest Mainland wet by
Saturday.

&&


.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...WSW 155.

MARINE...Storms: 119 120 130 131 132 138 160 352.

Gales: 125 129 136 137 139 140 141 150 155 165 180 181 185 351
414.

FIRE WEATHER...NONE.

&&

$$

SYNOPSIS AND MODEL DISCUSSION...KO
SOUTHCENTRAL ALASKA...BL
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...AH
MARINE/LONG TERM...MM/PD



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