Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
340 PM EDT Tue Jun 25 2019
Valid 12Z Sat Jun 29 2019 - 12Z Wed Jul 03 2019
Model guidance continues to suggest that the northern extent of
the upper ridge will breakdown through the medium range period,
allowing for portions of the mainland to be influenced by a
stronger and more active westerly mid/upper-level flow. Although
there is a decent signal for a weakening frontal system crossing
the Aleutians and into western portions of the mainland; which the
associated shortwave that will knock down the ridge. Variability
in regards to timing, strengthen and placement within the guidance
keeps much of this forecast with below average confidence. The
starting point was primarily a blend of the 06/12Z GFS, 00Z
ECWMF/CMC; with increasing weighting of the 00 ECWMF/12Z NAEFS and
GEFS means by late in the forecast.
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/Campbell
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