Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
650 PM EDT Thu Mar 19 2020
Valid 12Z Mon Mar 23 2020 - 12Z Fri Mar 27 2020
...Overview and Guidance/Predictability Assessment...
Resilient upper ridging will continue to meander over the
northeast Pacific next week, shifting between 150W-180. With an
upper low forecast to slide eastward along 80N from the New
Siberian Islands through the Arctic Sea toward Banks Island by
midweek, a fast upper jet will move across the Interior in two
phases. This may lead to a cold push of air late next week but
there remains a large amount of ensemble spread by then.
A blend of the 12Z deterministic models (GFS/ECMWF/UKMET/Canadian)
offered a reasonable starting point for the Mon-Wed forecast south
of 60N as a modest upper low lifts across the eastern Aleutians
and back southeastward south of the Gulf. To the north, the GFS
and UKMET were much quicker with a system through the North Slope
than the Canadian/ECMWF and no appreciable trend was noted in
either camp. Despite the better continuity in the ECMWF to the
south, the quick flow between the upper low to the north and upper
ridge to the south (in addition to upstream uncertainty) may not
support a solution as slow as the ECMWF, so a blended/middle
ground solution was preferred. By the end of next week,
deterministic solutions became much more aggressive to lower
heights across most of the mainland but given inconsistent
previous runs and large ensemble spread, opted to only partially
blend in some of the GFS/ECMWF/Canadian with much more of the
ensembles.
...Weather Highlights/Threats...
Well above average temperatures across the North Slope will give
way to near average or below average temperatures through the
week, especially over the eastern Interior. A warm front on Monday
will bring some snow to northwestern areas (Kotzebue to Utqiagvik
and points eastward) with light to modest accumulation. A more
expansive area of snow is likely on Tuesday ahead of a cold front
that will temporarily stall north of the Tanana Valley before then
dropping southward later in the week. Much colder air will push
through most of the interior, especially eastern sections, but the
veracity of the cold is uncertain. The deterministic models
showed, perhaps, the extreme solutions whereas a guarded/blended
solution was only modestly cold. NW flow should trend most of the
mainland drier as another system in the Bering moves eastward
through the Aleutians next Thu/Fri.
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 snow across portions of mainland Alaska, Sun-Mon, Mar
22-Mar 23.
- Heavy snow across portions of mainland Alaska, Mon-Tue, Mar
23-Mar 24.
- Much above normal temperatures across portions of mainland
Alaska, Sun-Wed, Mar 22-Mar 25.
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