Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
552 PM EST Mon Feb 24 2020
Valid 12Z Fri Feb 28 2020 - 12Z Tue Mar 03 2020
After getting a better handle on the large scale flow pattern
across Alaska during the extended period, guidance continues to
struggle with some of the details of individual systems. An
upper-level high across eastern Siberia will allow for increasing
influence from arctic shortwave energy across much of mainland
Alaska, with another round of very cold temperatures likely.
Farther south, a very active North Pacific storm track will
persist across the Aleutians, with the potential for a deep
surface low to move into the southern Bering Sea by the weekend.
Models/ensemble show general consensus that a rapidly deepening
low pressure system should approach the Aleutians and move into
the southern Bering Sea Fri-Sat, potentially bringing high winds
to portions of the Aleutians and the Alaska Peninsula. Models show
some disagreement on the precise track/timing of this feature, but
overall broad agreement on the deep nature of the system. The
ECMWF seemed to be the solution most well-centered within the
ensemble spread, and thus was weighted heavily in the forecast
during days 4-5 (Fri-Sat) along with a smaller component of
ECENS/GEFS ensemble means. By Sun the system is forecast to begin
moving eastward across the Alaska Peninsula and southern mainland
Alaska, with model spread gradually increasing. The system is
expected to bring a period of widespread snow to the Alaska
Peninsula and much of southern mainland Alaska, with rain across
the Aleutians. There was some signal in the guidance of another
similar (perhaps not quite as deep) low pressure system
approaching the Aleutians by next Tue, although spread was quite
high surrounding this feature, and confidence in the specifics
low. Weighting of ensemble means was gradually increased during
the day 6-8 (Sun-Tue) time period to account for the increasing
spread.
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
Hazards:
- Heavy precipitation across portions of the Alaska Panhandle and
mainland Alaska, Thu, Feb 27.
- High winds across portions of mainland Alaska and the Aleutians,
Sat-Sun, Feb 29-Mar 1.
- Much below normal temperatures across portions of mainland
Alaska, Thu-Mon, Feb 27-Mar 2.
- Much below normal temperatures across portions of far northern
mainland Alaska, Thu-Fri, Feb 27-Feb 28.
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