Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
350 PM EDT Tue Jun 12 2018

Valid 12Z Sat Jun 16 2018 - 12Z Wed Jun 20 2018

...Heavy rainfall expected along the southern Alaskan coast into
the panhandle...

...Guidance Assessment and Weather Highlights...

At the onset of the period, models show a vigorous surface low
crossing the Aleutians on Saturday morning. This would be the
extratropical remains of former western Pacific tropical storm
Maliksi. The accompanying mid-level low will be comprised of
fairly significant anomalies, generally on the order of 2 sigma
below mid-June climatology. With extensive downstream ridging in
place, the mentioned upper low should be forced poleward while
weakening across the eastern Bering Sea. On its heels, another
lobe of vorticity begins to lift up toward the northeastern
Pacific by Monday before pushing inland early next week. Across
the more Arctic latitudes, a semi-permanent upper low should spin
about the region with continued meandering likely into the
following week.

There is remarkable model agreement through the weekend with all
global solutions supporting a deep extratropical cyclone crossing
the Aleutians early Saturday. The larger divergence in the models
is with the next shortwave primed to affect the south-central
Alaskan coast by Monday. While all agree on the existence of the
attendant surface low, they vary with details and location. Thus,
started to move toward a more ensemble-based approach from Monday
onward. Through the weekend, favored the 12Z/06Z GFS and 00Z ECMWF
rather heavily before shifting toward greater use of their
corresponding ensemble means. By Day 8/June 20, took an equal
split of the 06Z GEFS/00Z ECMWF ensemble means.

With the highly meridional pattern in place, impressive
subtropical moisture fluxes will stream northward toward the
southern Alaskan coast. In advance of each surface cyclone,
particularly the one Saturday morning, 850-700 mb moisture flux
anomalies move into the 3 to 4 sigma above average range. Recent
guidance suggests 1 to 2 inch 12-hour amounts are possible during
any of this tropical surges. 5-day totals could equate to several
inches anywhere along the southern Alaskan coast eastward to the
panhandle. In addition, some gusty winds are likely during some of
these rainfall events.



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