Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
549 PM EST Fri Feb 21 2020
Valid 12Z Tue Feb 25 2020 - 12Z Sat Feb 29 2020
After quite a bit of variability among guidance over the last few
days on the expected evolution of the large scale flow across
Alaska next week, spread among model guidance seems to have
reduced somewhat. Some important differences remain, however, even
at the larger scales, and the specific details of individual
systems continue to be quite murky at best. A relatively weak
upper-level ridge axis across Southeast Alaska and western Canada
is expected to quickly erode by the middle to end of next week,
while a closed upper-level high, separated from the main ridge,
should gradually weaken across the northern Bering Sea. This setup
will allow for increasing influence from arctic flow across much
of mainland Alaska, with another round of very cold temperatures
looking likely. Farther south a very active North Pacific storm
track will plague the Aleutians and the Gulf of Alaska with
frequent low pressure systems spaced 24-36 hours apart.
A relatively deep area of low pressure is forecast to move
northeast across the Gulf of Alaska Tue-Wed. Models had quite a
bit of spread on the timing and exact track of this low. The UKMET
was the solution most well-situated in the center of ensemble
member spread (and was also relatively close to forecast
continuity), this the UKMET was weighted heavily in the forecast
during days 4-5. By day 6 (Thu) another similar low pressure
system is forecast to enter the Gulf of Alaska, with spread a bit
higher than the first - warranting an increase in weighting of
ensemble means (ECENS and GEFS). Both of these systems are
expected to bring potentially heavy precipitation to portions of
southern mainland Alaska and the Alaska Panhandle. Farther west,
models show the potential for a couple significant low pressure
system to affect the Aleutians later next week (Thu night through
Sat). Due to high variability and spread among deterministic
guidance, leaned much closer to ensemble means by later next week,
along with some use of the ECMWF, which was reasonably
well-centered within the ensemble 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, Tue-Thu, Feb 25-Feb 27.
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