Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
323 PM EDT Fri Mar 23 2018

Valid 12Z Tue Mar 27 2018 - 12Z Sat Mar 31 2018

The large scale pattern from the north Pacific and Alaska is
expected to shift toward a blockier setup during the medium range.
Models/ensembles show good agreement that a decaying/barotropic
low pressure system will be located across the eastern Bering Sea
on day 4 (Tue). Models show good consensus that this low will
linger into mid-week before finally dissipating. Farther east,
there remains some disagreement among the guidance as to how
strong a ridge axis extending from western Canada into the Arctic
Ocean will be early in the medium range period. The ECMWF remains
the strongest with this feature, continuing to depict a cutoff
upper ridge over the Arctic. Meanwhile the GFS remains the
weakest, although it has trended toward a stronger ridge over the
past 24 hours. The CMC remains a middle ground solution with
respect to the ridge. The ECMWF/CMC have relatively strong support
from a significant number of ECENS and CMCE/NAEFS members, while
the GEFS largely resembles the GFS. Thus, as was the case
yesterday, continued to favor a blend of the ECMWF/CMC along with
the ECENS/NAEFS ensemble means.

Confidence was sufficient to use a majority of deterministic
guidance in the blend on days 4-5. This solution shows a surface
low entering the Gulf of Alaska on Wed, reaching Southeast Alaska
by Thu. Uncertainty continues to increase later in the period as
the pattern becomes more blocky across the North Pacific. The
GFS/GEFS are very aggressive with building a ridge across the
Bering Sea by mid to late next week, with a deep cutoff low over
the North Pacific, with perhaps formation of a Rex block. The
ECMWF/CMC and their respective ensembles have shown varying
degrees of support for this scenario. Thus, confidence is
relatively low for that time frame. There appears to be a
consensus that a ridge will develop across the north Pacific,
perhaps into the Bering, but just how strong the ridge will be is
unclear. Additional uncertainty enters the forecast late in the
period when, dependent on the amplitude of the Bering ridge, there
is some potential for Arctic shortwave energy to dive southward
into the state. Given these considerations, weighting was shifted
toward the ECENS/NAEFS means in the forecast beyond day 5.

In terms of sensible weather, rising heights across Alaska will
mean gradually increasing temperatures through the medium range
period. Initially near average temperatures early next week will
reach several degrees above average by mid-week. Areas of
precipitation are expected across southern/southeastern Alaska
Tue-Wed under the influence of the Gulf frontal system. Meanwhile,
ridging across east central/northern Alaska will result in dry and
relatively cloud-free conditions at least through mid-week.

Ryan