Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
330 PM EDT Mon Mar 18 2019
Valid 12Z Fri Mar 22 2019 - 12Z Tue Mar 26 2019
...Weather Highlights/Hazards...
Guidance still highlights a stormy weather pattern quite favorable
for multiple periods of terrain and coastal convergence enhanced
precipitation especially into the southern coast of the Mainland
as well into Southwest and northern Southeast Alaska through this
medium range period. Moist inflow will continue to wrap around an
prolonged and active series of deep Gulf of Alaska surface lows
that re-develop and interact as energies work under influence of
an amplified mid-upper level mean trough/closed low. Systems will
tap atmospheric rivers to produce daily totals averaging several
inches with some additional and locally favored multi-day totals
of 10+ inches. The airmass quickly loses moisture content farther
inland, but continue to expect modest snows inland from southwest
Alaska to the western/central Interior to northern Alaska as
energy lifts in a channel between a Bering Sea mean mid-upper
level trough/low and an Interior Alaska/western Canadian mid-upper
level ridge. Relatively dry conditions are expected to persist for
much of the east-central Interior under that ridge.
Meanwhile, expect stormy conditions for the Bering Sea/Aleutians
this period as deep surface lows develop under a mean closed upper
low/trough position. Models and ensembles have shown quite a bit
of run to run variance recently, lowering forecast confidence in
particular solutions. Highly unsettled weather will accordingly
work steadily underneath and eastward with system progression
through the Aleutians and toward the Alaska Peninsula/southwest
Alaska with triple point low transitions downstream of the deep
parent lows.
...Guidance Assessment...
A composite guidance solution seems reasonable for Friday when
forecast spread is relatively low. After consultation with local
Alaskan WFOs, the WPC Alaskan Days 5-8 product suite was then
mainly derived from ensemble means amid growing uncertainty with
emphasis on the ECMWF ensemble mean to maintain best continuity.
Schichtel
Bullet points from the WPC Days 3-7 Hazards chart can be found at:
https://www.wpc.ncep.noaa.gov/threats/threats.php
- Heavy precipitation for southern mainland Alaska, Thu-Sat, Mar
21-Mar 23.
- Heavy precipitation for the Alaska Panhandle, Sun-Mon, Mar
24-Mar 25.
- High winds for southern mainland Alaska and Aleutians, Thu-Fri,
Mar 21-Mar 22.
- High significant wave heights for coastal southern mainland
Alaska, Fri, Mar 22.
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