Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
659 PM EDT Tue Aug 17 2021
Valid 12Z Sat Aug 21 2021 - 12Z Wed Aug 25 2021
...Overview and Guidance Evaluation...
The extended range period over Alaska region begins with a closed
upper level low which should lift across the central/eastern
Aleutians and into the southeast Bering Sea this weekend before
opening up into broad troughing and slowly drifting east into the
western Mainland next week. The latest suite of guidance shows
good agreement on the large scale with this feature, but continues
to struggle with individual perturbations through the base of the
trough, particularly later in the period. Farther north, a compact
closed upper low should slide just north of Alaska which likely
drives a cold front into the Northern Slope region. Again, the
models show good agreement early on, with diverging timing and
strength solutions later on. Across the board, a general model
blend between the 12z GFS, ECMWF, and CMC was used for days 4-5.
After that, increased contributions from the ensemble means in
order to mitigate some of the details. Continued some minor
inclusion of the deterministic models just for some added
definition to individual systems. This approach maintained
reasonable continuity with yesterdays WPC forecast.
...Weather/Threats Highlights...
The system expected to track across the Aleutians into the
southern-southeastern Bering Sea and eventually the Mainland
should bring wet and unsettled weather across much of the Alaska
region. Organized rainfall is likely from the Aleutians and the
Alaska Peninsula this weekend, extending into the mainland from
late weekend into next week as low pressure continues eastward.
Some of this moisture will likely extend into the mainland from
late weekend into next week as low pressure continues eastward.
There are still significant detail differences that affect the
coverage and intensity of the precipitation at that time. Some
areas of moderate to heavy totals are possible with the best
signal currently along/near the southern coast into the Panhandle.
Gusty winds are also likely along coastal locations from the
Western Mainland, across the eastern Aleutians, the Peninsula, and
into the Southern Coast. Meanwhile precipitation should accompany
the cold front dropping into the northern mainland but with
lighter totals. By the first part of next week there will be a
question of how much moisture with the system to the south may
interact with the front.
The forecast continues to show below normal high temperatures over
much of the state through the period but with some daily
variability with system progression. Anomalies are likely to trend
colder over northern areas during the latter half of the period
behind the Arctic cold front. Lows should be more moderate with
various areas of above/below normal readings. Best potential for
above normal lows will be over some southern areas early and late
in the period and over the North Slope on Saturday ahead of the
Arctic front.
Santorelli
No significant hazards are expected over Alaska during this
forecast period.
Additional 3-7 Day Hazard Information can be found on the WPC
medium range hazards outlook chart at:
https://www.wpc.ncep.noaa.gov/threats/threats.php
WPC medium range Alaskan products including 500mb, surface
fronts/pressures progs and sensible weather grids can also be
found at:
https://www.wpc.ncep.noaa.gov/alaska/ak_5dayfcst500_wbg.gif
https://www.wpc.ncep.noaa.gov/alaska/akmedr.shtml
https://www.wpc.ncep.noaa.gov/alaska/ak_5km_gridsbody.html