Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
323 PM EDT Thu Aug 15 2019
Valid 12Z Mon Aug 19 2019 - 12Z Fri Aug 23 2019
A relatively extratropical strong surface low originating from
Tropical Storm Krosa (currently in the vicinity of Japan) will be
the most significant feature on the map for Alaska during the
extended forecast period as it tracks along/near the Aleutian
Chain and perhaps toward the Alaska Peninsula by late next week.
The ECMWF appeared reasonably well-centered within the ensemble
spread with respect to this system through much of the forecast
period. Given the origin of the low (extratropical transition),
have less uncertainty concerns than typical for going a bit deeper
with the low (as shown by the deterministic guidance),
particularly early in the forecast period. Farther east, a blocky
pattern initially in place with an upper high over the Bering Sea
and upper low over the eastern Gulf looks to break down, but the
pattern remains somewhat amplified (as would be expected
downstream of an extratropical transition), and by later next week
there's some consensus on a broad upper trough extending across
mainland Alaska. The North Slope will potentially be subject to
flow off the Arctic in this setup, although solutions do differ as
to exactly how much the upper high breaks down and/or migrates
westward which introduces some degree of uncertainty in the flow
at higher latitudes across Alaska. The WPC forecast was initially
based heavily on the deterministic 00Z ECMWF, with a gradual shift
to heavier weighting of ECENS/GEFS ensemble means through time.
Ryan
Additional 3-7 Day Hazard information can be found on the WPC
medium range hazards chart at:
https://www.wpc.ncep.noaa.gov/threats/threats.php
No significant hazards are expected over Alaska during this
forecast period.
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