Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
300 PM EDT Tue May 01 2018

Valid 12Z Sat May 05 2018 - 12Z Wed May 09 2018

Trough/ridge upper pattern will settle over Alaska next week
across the Bering/Panhandle downstream of another upper ridge over
northeastern Russia. This will bring a new system across the
Bering through the Aleutians next Sun-Tue before being blocked
east of the Gulf by the ridging over NW Canada next Wednesday.

Exiting system on Saturday will lift through SW Alaska and bring
its weakening occluded/warm fronts into the interior as the cold
front stalls and then dissipates over the Gulf Sun/Mon. Models
have trended a bit slower/stronger with this system and formed a
reasonable consensus (with some lingering timing spread) so a
blend of the 12Z GFS and 00Z ECMWF/UKMET/Canadian offered a good
starting point. 12Z GFS was then closer to the ensemble consensus
(06Z GEFS and 00Z ECMWF ensemble mean) with the Bering system and
used that as the primary deterministic weight to the forecast.
Kept the Canadian/ECMWF along for some details to enhance the
ensemble means. With building ridging to the east next Tue/Wed,
the parent low appears to get stuck near Bristol Bay as the triple
point low takes the front to the southeast.

Near to below average temperatures are expected over most of the
state for the period thanks to below average heights. Eastern
areas will see a trend toward and above average next week as
ridging pokes in from the southeast. Rainfall/mountain snowfall
will be focused over coastal southcentral areas into the Panhandle
where the 00Z GEFS reforecast QPF showed "MAX" values --
indicating a heavy precip signal for this time of year. Rain and
mountain snow will exit the interior/Panhandle by Monday ahead of
the Bering system next week, which will bring in another round of
modest precipitation so at least the Aleutians and Kodiak.


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