Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
606 PM EDT Sun Apr 11 2021
Valid 12Z Thu Apr 15 2021 - 12Z Mon Apr 19 2021
...Overview...
A highly amplified/blocky flow pattern is expected later this week
into early next week, especially over the mid-latitudes northward
to the lower high latitudes. This will feature an upper low
meandering south of Kodiak, generally between 40-50N, with ridging
to its north over much of Alaska south of the Brooks Range. To the
north, a shortwave will ride eastward through the Beaufort Sea and
drag a cold front across the North Slope.
...Guidance/Uncertainty Assessment...
The GFS paired well with the other 12Z guidance with the initial
upper low drifting southward later this week. However, it
continued to be likely too quick with the flow out of northeastern
Russia and through the Bering into the North Slope compared to the
ECMWF-led consensus. This again resulted in the GFS/GEFS becoming
out of phase with the ECMWF/Canadian ensembles. Upstream pattern
shows another deeper trough over Japan that will continue the
amplified flow, suggesting a slower pattern overall. The GFS/GEFS
have had several days of being too quick in the 5-7 day range only
to trend slower within about 4 days. Preferred the 12Z ECMWF
overall with support mostly from the UKMET and somewhat the
Canadian (but mostly the Canadian ensembles). This maintained good
continuity.
...Weather/Hazards Highlights...
With the main system south of the mainland, precipitation will be
generally light over the state. Relatively modest precipitation is
expected over northern areas as the shortwave and cold front push
across the North Slope. Some enhancement is possible on the
western side of the Brooks Range, northeast of Kotzebue. As the
Pacific upper low and occluded front drift back northward early
next week, some rain may try to push toward the Panhandle.
Temperatures will be milder than average for especially northern
areas of Alaska with southwesterly flow ahead of the cold front.
Parts of the Panhandle and southeastern Alaska may see near to
below normal temperatures with high pressure nearby over the
Yukon.
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