Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
321 PM EDT Tue Apr 17 2018

Valid 12Z Sat Apr 21 2018 - 12Z Wed Apr 25 2018

...Guidance/Uncertainty Assessment and Weather/Threats
Highlights...

The 12 UTC GFS/ECMWF and 00 UTC ECMWF/ECMWF ensemble mean have
become increasingly well clustered compared to prior runs,
bolstering forecast confidence to above normal levels. A blend of
these guidance pieces created a reasonable first guess for the WPC
medium range Alaskan product suite. This suite includes 500mb and
surface fronts/pressures progs and sensible weather grids that can
be found at:

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

In this scenario, an amplified upper ridge to the northwest of
Alaska in blocky weekend flow should allow height falls to dig
southwestward downstream over the interior. The models and
ensembles have struggled with the track of this cooling upper
trough/closed low, but have converged upon depiction of an
amplified system sufficient to squeeze out limited moisture to
produce some moderate snows.

Meanwhile, an energetic storm track flows underneath from the
north Pacific with a lead deep low to steadily track from just
south of an unsettled Aleutians Saturday to the nrn Gulf of Alaska
Sunday/Monday.This threatens maritime interests with heavy
winds/waves and moisture wrapping around the low/frontal system
will combine with terrain to fuel a southern to southeastern
Alaska heavy precipitation threat. Upstream, a second deep low in
this series is expected to near the wrn Aleutians by late weekend
and a potential subsequent storm track across the Aleutians and
southern Bering Sea Sun-next Wed would bring another risk of heavy
wind/waves/precipitation in an active flow pattern with overall
above normal predictability. 

Schichtel