Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
643 PM EDT Mon Apr 12 2021

Valid 12Z Fri Apr 16 2021 - 12Z Tue Apr 20 2021

...Overview...

A highly amplified/blocky flow pattern is expected later this week
into early next week, forced by positive height anomalies nosing
into the western Bering Sea (+2.5 sigma) and even stronger
anomalies (+3 sigma) over northwestern Canada as a closed high
anchors over British Columbia/Yukon. This favors an upper low in
between but south of the mainland, generally south of 50N until
perhaps next week. To the north, two shortwaves will ride eastward
through the Beaufort Sea and each drag a cold front across the
North Slope. Precipitation will generally be light over the area
with abundant high pressure.

...Guidance/Uncertainty Assessment...

The GFS and GEFS remained displaced and generally faster with the
flow over the higher latitudes (north of ~60N) which has been
ongoing for several days. Again today, favored the ECMWF/ECMWF
ensembles which were generally slower and more amplified along
with the UKMET and Canadian/Canadian ensembles at times. Multi-day
trend has shown the GFS gradually slowing down toward the ongoing
ECMWF idea but with expected shufflings of the players. Trend with
the upper low south of the Gulf and wound-up occluded front has
been a bit farther north but it will still be fighting strong
ridging to its north/northeast. A future player could be a
tropical cyclone in the western Pacific that may recurve off Japan
per the ensemble guidance next week.

...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 initial and second shortwave
and cold fronts 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 and Southcentral (especially Kodiak and the southern
Kenai peninsula) but would likely be light.

Temperatures will be milder than average for especially northern
areas of Alaska with southwesterly to westerly flow ahead of the
cold front and well above normal 850mb temperatures. Parts of the
Panhandle and southeastern Alaska may see near to below normal
temperatures with high pressure nearby over the Yukon despite a
surge of warmth aloft.

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