Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
425 PM EDT Sat May 19 2018

Valid 12Z Wed May 23 2018 - 12Z Sun May 27 2018

The period covering the middle to end of next week will be
dominated by general negative height anomalies encompassing the
Aleutians eastward into the northeastern Pacific. A lead upper low
sweeping across the Gulf of Alaska early Wednesday should
eventually reach the northern extent of British Columbia by the
evening hours. At this point, the 12Z/06Z GFS appeared to be
quicker outliers and were thus minimized in the forecast package.
Thereafter, a much more extensive upper trough will take over much
of the domain as a 522-dm mid-level low migrates across the
southern Bering Sea/Aleutian chain on Wednesday/Thursday. Heights
will continue to build in advance of this feature allowing for
broad ridging across much of western Canada. This system should be
the primary area of focus given cool, wet conditions it will bring
to the southern/southeastern Alaskan coasts. The 12Z GFS and 00Z
ECMWF seem to offer a pair of scenarios with the latter favoring a
more pronounced upper trough across eastern Alaska and points
southward. After coordination with local forecast offices, the
preferred route would be to follow a more 00Z ECMWF/ECMWF ensemble
mean based approach. This solution keeps troughing into the
picture for much of the period before ensembles really start to
build up heights over western Canada by next weekend.

Overall impacts from this pattern will keep wet conditions in the
picture from the Aleutians eastward along the entire extent of the
southern/southeastern Alaskan coast and along the panhandle. Ample
moisture guided toward the coast could produce 12-hour rainfall
amounts in the 0.50-1.00" range. Farther inland, some more showery
activity is expected across central sections of the state,
particularly in the presence of ample daytime heating.
Additionally, this will likely also be the warm spot over the
state as highs each day reach the low to possibly even mid 60s.


Rubin-Oster

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