Area Forecast Discussion
Issued by NWS Anchorage, AK

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FXAK68 PAFC 230046

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
446 PM AKDT SAT OCT 22 2016


Another omega block in the upper levels has set up across western
Alaska this afternoon. The associated ridge axis is aligned along
the west coast, with the pair of upper lows centered south of the
Gulf of Alaska on the east side, and over the far western
Aleutians near Attu on the west side. The omega block will prevent
significant changes to the weather over Southcentral from the
current sunny and cold conditions.

Southcentral`s primary weather concerns today involve areas of
very windy conditions. This morning, Thompson Pass had gusts to 70
mph, with gusts over 60 mph being reported in Valdez proper.
Strong high pressure over interior Alaska is drawing cold, dense
air southward towards the low over the Gulf. Thus, the passes that offer
the path of least resistance are those experiencing the strongest
winds, which include Thompson Pass, the Valdez Narrows, the Copper
River Delta, the Seward area, and Cook Inlet.

For Southwest Alaska, surface ridging extends right through the
area, as would be expected with the axis of upper level ridging
also overhead. As such, most of Southwest Alaska is also seeing
full sunshine, but for most areas away from the Alaska Range,
without the winds. High clouds are moving into coast regions from
the Kuskokwim delta north and west ahead of the next storm over
the Bering.

The most active weather once again is occurring over the Bering
and Aleutians today. An atmospheric river of moisture is streaming
north out of the tropics ahead of a strong low moving through the
western Bering. Gusty conditions are occurring along the entire
Aleutian chain. The plume of moisture has been moving eastward
quickly enough that precipitation amounts thus far have been
relatively light.



The models remain in good agreement today through the short term
forecast. The NAM and Hi-Res models were used on the east side,
where winds are the most pertinent forecast concern, to better
handle local effects. Meanwhile out west, the GFS22 was the
preferred model. Forecast confidence is high. Some forecast
challenges will be determining the magnitude and timing of the
peak wind speeds on the east side, as some gusts have been
approaching high wind criteria this morning. Out west, the
challenge will also be determining how strong the winds will get
over the Bering, and the evolution of upcoming potentially
stronger lows moving into the Bering from the Pacific in the
coming days.



The arctic trough is now digging into the North Pacific with
weakening northerly flow aloft over the region. This is allowing
for clearing skies and a weakening of the pressure gradient, the
latter of which will slacken dramatically overnight. Associated
offshore winds will also weaken, but with cold air in the
interior, this will keep a weak offshore drainage flow.

Tonight through Sunday, with ridging building in aloft from the
west, expect warming temperatures aloft. However, due to strong
inversions and colder nights, temperatures at the surface,
including during the day, will not feel this recovery of
temperatures aloft, so expect cold night and cooler days.



High pressure will keep southwest AK generally clear, cool and
dry through Sun night. A decaying front will move inland Sun
night, with clouds affecting the coast into Mon.



A strong front will bring rain and gales to the central Aleutians
and Bering tonight, and small craft wind to the eastern Aleutians
Sun, before weakening over the AK peninsula on Mon. The next
system will spread more rain beginning Sun night, and potentially
dangerous wind to the western and central Aleutians on Mon.


.LONG TERM FORECAST (Days 3 through 7)...
An amplified upper level ridge continues to build over the
Southwest/Southcentral region as we head into Monday time-frame.
Therefore, northerly offshore flow influences the Southcentral
region accompanied by colder air filtering into the region
through the upcoming midweek. By Wednesday morning this synoptic
featured will exit the region into the Yukon Territory. This
allows southwesterly flow with warmer temperatures to advect into
the Southcentral region through the next several days. Meanwhile,
several storms track through the Bering with the first storm
force low tracking just west of Shemya with an associated weather
front moving through the Western Aleutians. While, upstream a 150
knot northwesterly jet streak digs into the base of the longwave
trough located just west of the Western Aleutians. This synoptic
feature progressively intensifies the a rapidly developing storm
force North Pacific Low located just south of Shemya by Monday
morning. The GFS model has been the most consistent, and depicts a
974 mb low near Kiska by Monday afternoon. This low will rapidly
intensifying to a 941 mb hurricane force low as it tracks west of
Saint Matthew Island by Tuesday morning. As this system tracks
through the Bering and the Western Aleutians look for strong gusty
south/southwesterly winds accompanied by widespread rain/stratus.
Therefore, look for warmer temperatures in the aforementioned
regions through next week. By Wednesday this systems exits the
region into the Eastern Siberian region. Then, another storm
force low enters the Western Aleutians with the same storm track
as the previous storms. This new storm exits the region into the
Eastern Siberian region by Friday morning. Therefore, in between
these systems the Bering/Aleutians will have a showery weather

The NAM/GFS models are in better agreement with the strength of
intensifying hurricane force low pressure system as it tracks
into the Western Bering by Monday afternoon. While, the ECMWF has
briefly come into better agreement with these models, but then
tracks this system way faster than the previous mentioned models.
The GFS continues to be the preferred model of choice. This system
will remain under close scrutiny for the possible weather impacts
as it tracks through the Bering.


PUBLIC...High wind watch zones 187 and 191.
MARINE...gales 127 171 173 174 175 177 178 179 185 411 412 413



LONG TERM...PD is the U.S. government's official web portal to all federal, state and local government web resources and services.