Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
632 PM EDT Tue Apr 20 2021
Valid 12Z Sat Apr 24 2021 - 12Z Wed Apr 28 2021
...Overview and Guidance/Uncertainty Assessment...
An overall quiet weather pattern is on tap for much of Alaska days
4-8. Latest guidance continues to depict a fairly blocky regime
during much of the extended range period, with a slowly westward
retrograding upper ridge/closed high dominating much of mainland
Alaska as ample northwest Canadian closed vortex energies slowly
work into the state. The period begins Saturday with a lead system
moving through the N. Pacific towards the Northwestern U.S. coast
as a couple of closed lows/systems make their way towards the
Aleutians. By Sunday/day 5, the pattern may consolidate into a
main low just south of the Aleutians as energies slide more
underneath the closed high. This will favor organized low pressure
system development at the surface. Models still vary on the
evolution and track of this low, related to uncertain ridge
transformation details over the mainland. Prefer persistence more
than transition in blocky patterns. Accordingly, the WPC forecast
for today used a blend of best clustered guidance of the 12 UTC
GFS/ECMWF and 12 UTC GEFS/ECMWF ensemble means with a focus on the
models days 4/5 transitioning to the ensemble means into days 6-8
consistent with growing forecast spread.
...Weather/Hazards Highlights...
Most of Alaska should remain warm and dry through much of the
period, with precipitation confined to the Aleutians/Alaska
Peninsula and vicinity, particularly associated with the low
pressure system Saturday into Monday as it drifts over or just
south of the islands. Light to moderate amounts are most likely. A
period of gusty winds and unsettled maritime conditions are also
likely in association with this storm.
The vast majority of the state should be well above normal in
terms of temperatures through much of the period, with the warmest
anomalies over the North Slope region and western areas of the
Mainland, especially through the coming weekend. Lowering heights
over northern and eastern Alaska early next week should help to
moderate temperatures back towards normal or even below as the
pattern aloft will tend to retrograde westward and allow frontal
passage. Elsewhere, the southeast should experience near or below
normal temperatures through the medium range period in offshore
flow to the north of a slowly exiting southeast Gulf of Alaska low.
Schichtel
Hazards:
-Much above normal temperatures across portions of mainland
Alaska, Fri-Mon, Apr 23-Apr 26.
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
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