Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
633 PM EDT Fri Mar 27 2020
Valid 12Z Tue Mar 31 2020 - 12Z Sat Apr 04 2020
...Below to much below normal temperatures across portions of
Alaska through the middle of next week...
An anomalous upper-level high centered across northeast mainland
Alaska early next week will displace arctic air southward to its
east and southeast, keeping much of mainland Alaska cold through
much of the week. High temperatures Tue-Thu are forecast to be
10-25 deg F below average across the southern half of mainland
Alaska, as well as much of Southeast Alaska, with the arctic air
mass expected to reinforce a persistent stationary frontal
boundary just offshore. The North Slope will be the significant
exception, where above normal temperatures are forecast through
the medium range. Ensemble show a general consensus that the upper
ridge should gradually weaken as it shifts eastward through the
middle of next week, eventually breaking down the strong arctic
connection and allowing temperatures across Alaska to begin slowly
warming. Surface high pressure across mainland Alaska should keep
conditions dry for many areas, while a relatively active storm
track across the North Pacific remains mostly south of mainland
Alaska, with some potential precipitation for the Aleutians, the
Alaska Peninsula, and perhaps southwestern mainland Alaska (where
heavy precipitation is possible by the middle of next week).
Models/ensembles continue to show some degree of consensus on the
idea of a deeper low pressure system moving into the Bering Sea
next Thu-Fri, with a potential pattern change in the works for
Alaska, as the removal of the blocking ridge present earlier in
the week potentially opens Alaska up to somewhat more progressive
westerly mid/upper-level flow (as shown by the GFS), or perhaps
even a more amplified, but still relatively progressive flow
regime (as indicated by the ECMWF). Ensemble means were generally
somewhere in between these two scenarios, and were preferred by
late next week.
The WPC forecast was initially based heavily on the 12Z ECMWF/GFS,
along with some use of the GEFS/ECENS ensemble means on day 4
(Tue). Starting on day 5 (Wed) and continuing through the
remainder of the extended forecast period, a gradual trend toward
heavier weight placed on ECENS/GEFS ensemble means was shown, to
counter the increasing spread by that time (as described above).
Ryan
Hazards:
- Heavy precipitation across portions of mainland Alaska and the
Aleutians, Wed-Thu, Apr 1-2.
- High winds across portions of the Alaska Panhandle and mainland
Alaska, Mon, Mar 30.
- Much below normal temperatures across portions of mainland
Alaska, Mon-Tue, Mar 30-Mar 31.
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