Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
317 PM EDT Thu Mar 28 2019

Valid 12Z Mon Apr 01 2019 - 12Z Fri Apr 05 2019

A blocking mid/upper-level ridge initially in place across
mainland Alaska at the beginning of the extended forecast period
(Mon) is expected to gradually migrate westward through next week.
By day 8 (next Fri) ensemble means show consensus that the apex of
the ridge should be centered across far northeastern Russia. The
predominant storm track through the period will be through a
region of persistent negative 500 hPa height anomalies well south
of mainland Alaska, and mostly south of the Aleutians. A number of
model solutions have shown shortwave energy of varying intensity
rotating around the ridge across mainland Alaska Tue-Wed before
entering the Gulf by Thu. The ECMWF and CMC were most similar in
their depiction of this feature, albeit at opposite ends of the
intensity spectrum (leading one to favor a blend of the two
solutions). Given similar depictions of the upper ridge through
the first few days of the forecast as well, the WPC forecast
during days 4-6 (Mon-Wed) was based heavily on a blend of the
ECMWF and CMC. The GFS showed a differing structure/evolution of
the upper ridge from early in the period which farther from
consensus, causing that solution to be excluded from the forecast.

By later next week, as the center of the ridge begins to move west
of Alaska, this would likely open mainland Alaska up to northerly
flow off the arctic, and the potential for a stream of incoming,
low-predictability arctic shortwaves. The ECMWF showed a larger
scale evolution most similar to the ensemble means, with a strong
closed ridge centered across/near far northeastern Russia by next
Fri. Thus, the forecast during days 7-8 was based heavily on the
ECENS/NAEFS ensemble means, with inclusion of a small component of
the deterministic ECMWF as well.


Ryan


Bullet points from the WPC Days 3-7 Hazards chart can be found at:
<a href="https://www.wpc.ncep.noaa.gov/threats/threats.php"><u>https://www.wpc.ncep.noaa.gov/threats/threats.php</u></a>

-No significant hazards are expected over Alaska during this
forecast period


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

<a href="https://www.wpc.ncep.noaa.gov/alaska/ak_5dayfcst500_wbg.gif"><u>https://www.wpc.ncep.noaa.gov/alaska/ak_5dayfcst500_wbg.gif</u></a>
<a href="https://www.wpc.ncep.noaa.gov/alaska/akmedr.shtml"><u>https://www.wpc.ncep.noaa.gov/alaska/akmedr.shtml</u></a>
<a href="https://www.wpc.ncep.noaa.gov/alaska/ak_5km_gridsbody.html"><u>https://www.wpc.ncep.noaa.gov/alaska/ak_5km_gridsbody.html</u></a>