Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
608 PM EST Tue Dec 24 2019
Valid 12Z Sat Dec 28 2019 - 12Z Wed Jan 01 2020
...Much below average temperatures to moderate a bit...
...Stormy pattern from Southcentral across the Gulf of Alaska...
Upper ridging over eastern Russia/Sea of Okhotsk and between
Hawai'i and California will support a positively-tilted trough
from around 50N (south of the Aleutians) across the AKPEN and into
the Gulf of Alaska. With an upper low slowly lifting away from the
Beaufort Sea, well below average temperatures will gradually
moderate but remain colder than average over the interior. The
exception will be for the Panhandle with above average
temperatures in a wet pattern.
The pattern remains sensitive to the orientation/evolution of the
upper trough and its southwestward extension into Bristol Bay on
Sunday. The trend has been toward a sharper/deeper trough that
would pull the storm track farther northwest than what the
consensus showed yesterday. Though the GFS yesterday was well NW
of the prior consensus, the newest 12Z deterministic consensus was
about halfway between new and old. The ensemble means were still a
bit flatter, with continued spread and no apparent convergence.
Opted to rely fully on the deterministic models to start (Sat/Sun)
with the lead system moving through the Panhandle and the next
system organizing south of the Aleutians. Thereafter, trended
mostly toward the ensemble means with only some influence of the
12Z Canadian and ECMWF as the GFS still took that parent low
across the AKPEN into Bristol Bay next Tue which may be possible
but has little support as of now.
Cold air (lows in the -40s south of the Brooks Range Sat) will
moderate about 5-15 deg F into next week but remain below average.
Trended colder again by the end of the period next Tue/Wed based
on the latest upper pattern (more troughing west of Southcentral,
swinging through from the NW) and introduced a sfc cold front.
Rainfall (and snowfall) will be quite heavy across parts of
Southcentral to the Panhandle given the storm track. Lows may
trend very close to the Kenai peninsula/Prince William Sound which
would bring in heavier snow (some coastal rain, Cordova to
Yakutat) to southeastern Kenai eastward through the Panhandle.
Fracasso
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, Fri-Sat, Dec 27-Dec 28and Sun-Tue, Dec 29-Dec 31.
- Much below normal temperatures across portions of mainland
Alaska, Fri-Tue, Dec 27-Dec 31.
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