Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
725 PM EDT Sun Mar 22 2020
Valid 12Z Thu Mar 26 2020 - 12Z Mon Mar 30 2020
...Turning colder for much of the Interior late next week...
Upper pattern will turn toward much lower heights over the
Interior of Alaska next weekend as upper ridging splits off
through the Bering Sea. The evolution of an upper low south of
Kamchatka has not been handled well at all the past couple of
days, and this ties to both the upper ridge strength/shape and
northern stream flow across far northeastern Russia. The end
result still comes together from various avenues, but how the
interim days sequence together remains hard to determine.
The ECMWF ensemble mean has been least susceptible to run-to-run
changes, mostly by definition, but at least provided a good
baseline to the forecast. West of 180, the splitting upper low
(perhaps now in three pieces and not two) may be slow enough to
allow the ridge to its east to surge northward and pinch off over
far northeastern Russia which would allow energy to shear eastward
into southwestern Alaska as the western part of an upper low over
the Canadian archipelago sinks southward. This would still bring a
swath of modest snow to the Interior, focused from the Alaska
Range northward, before it all pushes into the Gulf next week
Sun/Mon. The 12Z GFS/Canadian/ECMWF had at least enough agreement
to use in the blend for some detail with the ECMWF ensemble mean
and 12Z NAEFS mean, maintaining an increasingly drier and colder
flow over the Interior/North Slope. Back to the west by next
weekend, flow looks increasingly westerly as the ensembles show
strong upper ridging beneath troughing over Kamchatka and a strong
jet (170kts?) near the western/central Aleutians.
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
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