Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
219 PM EST Sun Feb 24 2019

Valid 12Z Thu Feb 28 2019 - 12Z Mon Mar 04 2019

The strong upper high will continue to be the dominant feature in
eastern Alaska through the medium range along with the mean upper
trough in the Bering Sea. Models and ensembles are in good
agreement with this overall pattern; however, the 00Z ECMWF and
its ensemble mean still maintains the upper high over eastern
Alaska longer--although the 06Z GEFS mean and the 12Z GFS has
trended toward this. Timing on the different systems moving
through the Bering Sea also differ in the different models but
still comparable enough to use in the blend.

In the beginning of the medium range period, the ridge will center
over eastern Alaska as the trough slides toward western Alaska
from Thu-Sat. A strong, occluded low will approach west Alaska on
Thu, with the boundary stalling by Fri and dying by Sat. This will
keep precipitation chances around for this region of Alaska along
with the western portions of the Aleutians--with the chances of
precipitation decreasing by Sat. On Sun, the ridge will shift into
western Canada as energy pushes through the ridge, with another
incoming mid-level low/strong occluded front approaching the
Bering Sea. Models and ensemble means have been consistent with
showing this surface low to be below 980mb, and as it approaches
western Alaska on Mon, guidance shows the surface low weakening.
Expect precipitation chances to increase on Sun and into Mon for
the Aleutians/western Alaska once again due to this system. The
WPC blend was based on the 12Z GFS/00Z ECMWF from days
4-5/Thu-Fri, with an increase in the 00Z ECMWF ensemble mean by
days 6-8/Sat-Mon, with some 06Z GEFS mean.

Most of the state will remain precipitation-free under the upper
high--with precipitation confined to the Aleutians and western
Alaska. Temperatures will be mostly above average but variable
through the interior due to inversions in the thermal profile with
little mixing. The greatest temperature anomalies will likely
occur across the North Slope into northwestern Alaska where
temperatures may exceed 25-35 deg F above average owing to
sustained southerly flow over lower/flatter elevations.
Temperatures over the Panhandle may be slightly below average due
to northeasterly/easterly flow out of Canada, especially next
weekend as the upper high slips northward and allows a cool push
of air to leak southwestward out of the Yukon.


Reinhart/Fracasso



WPC medium range Alaskan products including 500mb, surface
fronts/pressures progs and sensible weather grids can be found at:

http://www.wpc.ncep.noaa.gov/alaska/ak_5dayfcst500_wbg.gif
http://www.wpc.ncep.noaa.gov/alaska/akmedr.shtml
http://www.wpc.ncep.noaa.gov/alaska/ak_5km_gridsbody.html