Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
301 PM EDT Fri Oct 19 2018

Valid 12Z Tue Oct 23 2018 - 12Z Sat Oct 27 2018

...Continued threat of heavy precipitation for
southern/southeastern Alaska...

The large scale pattern across Alaska will remain relatively
unchanged through the extended period, with a broad mean upper
trough extending from western mainland Alaska south to the North
Pacific, and multiple smaller scale shortwaves traversing the
larger scale trough. This pattern will result in a sustained
period of southerly flow into Alaska from lower latitudes, with
embedded systems enhancing precipitation potential. While models
show agreement on the larger scale, there continues to be
disagreement on the specific details of individual systems. Models
do show general agreement on a multi-day heavy precipitation event
for portions of southern and southeastern Alaska with multiple
inches (liquid equivalent) of precipitation likely, especially at
windward locations near the coast. The flow regime will meanwhile
inhibit the southward expansion of arctic air across Alaska.

The ECMWF/GFS/CMC were reasonably well clustered around an
ensemble-mean based consensus early in the extended period, and
the suite of WPC Alaska medium range products was based heavily on
these solutions during the day 4-5 (Tue-Wed) time frame. For days
6-8 (Thu-Sat), as model spread with respect to individual systems
increased, weight was shifted toward the ECENS/GEFS ensemble means.

Ryan


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