Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
327 PM EDT Tue May 22 2018

Valid 12Z Sat May 26 2018 - 12Z Wed May 30 2018

...Guidance/Predictability Assessment...

Guidance clustering has improved some with the last couple run
cycles, bolstering forecast confidence closer to average levels.
Model run to run variance still offers some timing/emphasis
challenges over time, so included a good portion of the latest
GEFS/ECMWF ensembles into the mix to maintain as much WPC
continuity as possible. Otherwise, the WPC Alaskan product suite
included some input from the ECMWF that seemed to be most in line
with main ensemble clustering.

...Weather/Threats Highlights...

Overall, it seems reasonably likely that two main deep lows will
highlight the weather forecast in the vicinity of Alaska days 4-8.
A lead low roams over the Gulf of Alaska this weekend, to weaken
early next week. Wrapping moisture will fuel high winds/waves and
widespread precipitation over the north-central and eastern Gulf
of Alaska that should increasingly spread onshore into southern
and southeastern Alaska with gradual low approach into early next
week. Guidance continuity trends toward a deeper low seems in line
with favorable upper support. Less defined/more chaotic vort
centers lingering overtop the interior offer less predictability
but overall suggest some periods of precipitation over the weekend
into next week underneath a arctic ridge bridging just to the
north of the state. Meanwhile, a second main low also has decent
guidance support whose approach into the Aleutians and southern
Bering Sea from the northern Pacific early to mid next week would
threaten the region with high winds/waves and sweeping
precipitation.

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

Schichtel