Area Forecast Discussion
Issued by NWS Anchorage, AK

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FXAK68 PAFC 151551 CCA
AFDAFC

Southcentral and Southwest Alaska Forecast Discussion...CORRECTED
National Weather Service Anchorage AK
651 AM AKST Wed Jan 15 2020

.ANALYSIS AND UPPER LEVELS...

A highly amplified upper level pattern has developed over the
Bering and mainland Alaska. A strong low currently centered over
the Kamchatka Peninsula is bringing moderate rain and gusty
southwesterly winds to the western Aleutians. A very sharp ridge
is seen upstream, extending all the way into the Arctic Ocean.
This is inhibiting any precipitation from developing from the
central Bering through Southcentral Alaska, although patchy fog
is indicated on satellite over portions of the Susitna Valley.
Farther east, a weak upper low centered near Fort Yukon is
resulting in a tight upper pressure gradient over the eastern part
of the state. As such, strong northerly outflow winds are being
observed in terrain gaps in the Copper River Delta as well as the
city of Valdez.

&&

.MODEL DISCUSSION...

As stated in the previous discussion, synoptic model agreement
remains good. There remains some uncertainty with regards to the
interaction between the strong front and a compact low pressure
system this morning over the central Bering. This will determine
the position of the strongest (storm force) southerly winds,
which at this time looks to be just west of Nikolski.

Likewise, there is good model consensus that the aforementioned
sharp ridge will develop into a closed upper level high and begin
to weaken in the coming 48 hours, leading to the gradual
diminishing of outflow gap winds.

&&

.AVIATION...

PANC...Patchy fog and hence brief LIFR ceilings will remain
possible through this morning. Winds will slightly increase this
afternoon, thereby causing any remaining fog to dissipate. This
scenario is likely to repeat on Thursday morning.

&&

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

The upper ridge over western Alaska amplifies today bringing a
strong northerly upper jet across Southcentral. This combined with
cold interior air and and strong surface gradients (temp/pressure)
will enhance outflow and gap winds across Southcentral today. Most
notably the North Gulf Coast local affect areas (Copper River Delta,
Valdez zone and surrounding marine areas, and Thompson Pass) where
gusts in the 50 to 60 mph range are expected today. The
aforementioned areas will remain fairly strong through tonight, but
will experience a slow downward trend through Thursday. Elsewhere,
winds over the eastern Kenai Peninsula/western Prince William Sound
will peak today and then slowly diminish. The upper ridge shifts
east later today and the upper flow becomes more northeasterly. That
combined with more favorable pressure gradients will enhance the
cold air spilling out of the Copper River Basin and give rise to
strong northeast winds across much of the Matanuska Valley. These
winds will likely hold through late Thursday. Many locations with
winds will experience brisk wind chills through Thursday, however
Thompson Pass is the only location expected to hit advisory (-40F)
conditions.

&&

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

Cold and clear conditions will persist across Southwest Alaska today
with an upper level ridge positioned over the Southwest coast
through Thursday morning. Gusty offshore flow will continue for the
Kuskokwim Delta and coastal areas of Bristol Bay, which will
slightly weaken through Friday afternoon. Temperatures will be on a
downward trend over the next few days as Southwest Alaska remains
mostly cloud-free, with frigid temperatures returning for the
Kuskokwim Delta and Valley by the end of the week. By Friday night,
most areas will likely see low temperatures below zero, with the
Lower Kuskokwim Valley dropping to 20 below zero.

&&

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

A north-south oriented front stretched over the central to eastern
Bering and Aleutians this morning will keep an active pattern
through Thursday night. Storm force winds will accompany this
system from Dutch Harbor toward the Pribilofs late this morning
through the afternoon, which should weaken to gale force strength
by later tonight. Dutch Harbor could see strong wind gusts from
60-70 mph peaking around the afternoon hours, but wind speeds
will likely stay under the warning level criteria.

Strong winds will persist as a surface low develops along the
front near the central Aleutians this afternoon. However, there is
some disagreement on the exact placement of this low, which will
affect where the strongest winds will be and how long they last.
In any case, strong southeasterly flow will persist over the
eastern Bering and Aleutians through Thursday evening, when the
front begins to lift northward and weaken.

By late Thursday morning, the next low pressure system will make
its way over the western and central Aleutians. The associated low
center will remain south of the Chain as it continues back into
the North Pacific through Friday afternoon.

&&

.MARINE (Days 3 through 5/Friday through Sunday)...

After a low exits south of the Aleutians Friday, conditions look
fairly benign through the weekend. For the Gulf, it looks like a
deep low will approach the Gulf Friday and possibly move into the
Gulf Saturday through Sunday. At this time, forecast confidence
in the track of this system is low. There is potential for gale
force winds sometime this weekend, most likely over the southern
to eastern Gulf.

&&

.LONG TERM FORECAST (Days 4 through 7/Saturday through Tuesday)...

For the Bering Sea and Aleutians, conditions look relatively quiet
over the weekend, with some weak systems transiting the Bering in
fairly flat upper level flow. Deep lows will track south of the
Aleutians, along the jet stream. Some model solutions bring a
deep low up to the Aleutians Monday night through Tuesday, but
confidence in this is low.

Meanwhile, Southcentral will remain cold and dry for the beginning
of the weekend as a large deep closed upper level high crosses the
northern half of Alaska. As the ridge continues eastward into
northwest Canada, this will result in a bit of a pattern change
as upper level features start to track northward across the
state. Of most interest to Southcentral Alaska, energy from a high
amplitude trough over the northeast Pacific will be pulled
northward into the Gulf as early as Sunday. This will bring
increased potential for snow to Southcentral Sunday through
Tuesday. At a minimum would expect an increase in clouds and and
upward trend in temperatures.

&&


.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...Wind Chill Advisory: 131.
MARINE...Heavy Freezing Spray Warning: 119 121 129 139 140 160
                                       180 185.
         Gale Warning: 127 155 165 171 175-181 185.
         Storm Warning: 170 172-174.
FIRE WEATHER...NONE.

&&

$$

SYNOPSIS AND MODEL DISCUSSION...AP
SOUTHCENTRAL ALASKA...RMC
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...AH
MARINE/LONG TERM...SB



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