Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
337 PM EDT Mon Jun 24 2019
Valid 12Z Fri Jun 28 2019 - 12Z Tue Jul 02 2019
A pattern change now appears likely across Alaska by late this
week with the expected breakdown of the northern extent of the
upper ridge, opening mainland Alaska up to stronger and more
active westerly mid/upper-level flow. Models show relatively good
consensus on a weakening frontal system crossing the Aleutians and
moving into western mainland Alaska late this week, with the
associated shortwave the mechanism for breaking down the northern
extent of the upper ridge. A blend of the ECMWF and GFS served as
a starting point for the forecast on day 4-5 (Fri-Sat), with a
gradual trend to heavier weighting of ensemble means (ECENS and
GEFS) starting on day 6 (Sun). The primary difference later in the
period revolves around the eventual evolution of this shortwave as
it moves east, with the ECMWF continuing to amplify the wave into
the Gulf of Alaska by Sun night-Mon and the GFS showing a period
of somewhat more zonal flow along the northern periphery of a more
elongated upper ridge. Ensemble means suggest something in between
these two scenarios may be a possibility, thus the use of majority
ensemble means by the latter portion of the forecast period was
warranted. This setup would bring an end to the drier conditions
seen across much of Alaska recently, with an increase in
moisture/showers for much of mainland and Southeast Alaska.
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