Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
209 PM EST Wed Nov 14 2018

Valid 12Z Sun Nov 18 2018 - 12Z Thu Nov 22 2018

The overall synoptic pattern across Alaska for the Day 4 (Sunday)
to Day 8 (Thursday) time period features an initial closed low and
associated surface system tracking eastward from the Alaska
Peninsula/eastern Aleutians into the Gulf of Alaska. Behind this,
another system crosses the Aleutians early next week, with yet
another one on its heels by mid-late next week. Strong upper
ridging across mainland Alaska in the beginning of the period
looks to break down as multiple systems push into the region.

There is decent agreement in the beginning of the period between
the 06z GFS/00z ECMWF/06 GEFS/00z ECENS with the pattern, but
bigger differences in details and timing with the operational
models arises after day 5. The most notable difference is the 00z
ECMWF which is on the fast side of the guidance with the initial
closed low/short wave entering the Gulf. It also provides a much
stronger short wave across the Aleutians on Day 5, which
eventually becomes a rather deep cyclone south of the Gulf in this
time. This evolution by the ECMWF is completely out of phase with
the GFS/GEFS and even its own ensemble mean and the confidence in
this particular solution is very low at this time. Despite minor
timing differences, there is rather good agreement through the
period between the GEFS/ECENS means and thus after day 5,
increasing percentages of the means was used in the overall blend
for the 500mb and pressure/fronts progs. For reasons discussed
above, removed the ECMWF after day 5, but did continue to include
a small bit of the 06z GFS which was the operational model most
closely matching that of the means. This overall blend gave a
forecast very close to yesterdays continuity as well. 

Regarding sensible weather impacts...heavy rainfall is expected
across the southern mainland Alaska coast and the Panhandle during
the weekend and into the beginning of next week associated with
the initial low pressure system. A brief break in the
precipitation looks likely by the middle of the week across the
southern Mainland, with another round of organized and locally
heavy precipitation moving into the Peninsula, southern coast, and
the panhandle regions by mid-late next week. Upper ridging holding
strong early in the period should keep temperatures above normal
across interior portions of the state, with temperatures returning
to closer to near normal values by the end of the period. 

Santorelli

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