Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
218 PM EST Sat Nov 17 2018

Valid 12Z Wed Nov 21 2018 - 12Z Sun Nov 25 2018

The overall synoptic pattern across Alaska for the Day 4
(Wednesday) to Day 8 (Sunday) time period features initial
troughing in the Gulf and over Alaska Wednesday - Friday, with
upper level ridging trying to build back in by the weekend. A
series of shortwaves/possible closed lows track across the
Aleutians, with systems at the surface tending to track near or
south of the Aleutians.

There is actually fairly good agreement on the basic synoptic
pattern through much of the period between the operational 12z
GFS/00z ECMWF and their respective means. After day 5 though,
differences in both timing and details of individual
systems/closed lows begin to arise in the operational models which
results in varying strength/placements of surface lows tracking
across the western Aleutians and south of the Alaska mainland.
There's also some differences in the timing of the ridge
rebuilding across the Gulf and southern Alaska day 7 to 8.
Run-to-run continuity in the operational models is poor so leaning
more on the ensemble means Day 6-8 is the best solution at this
point. The blend for this cycle of the WPC Alaska 500mb and
pressure/fronts progs used a majority GFS/ECMWF blend Days 4-5,
with increasing weighting of the ensemble means through the
remainder of the period. Even through day 8, did continue to
include small percentages of the operational models in an attempt
to gain some degree of detail/amplification in systems rather than
the flat/washed out flow shown by the ensemble means (presumably a
result of large differences in individual ensemble members). The
overall forecast pattern maintains good continuity with yesterdays
forecast as well.

Regarding sensible weather impacts...an overall drying pattern can
be expected across much of the state through most of the period,
with maybe some lingering showers early in the period for the
Panhandle or the southern Coast region. Systems tracking over or
south of the Aleutians should bring another round of rain, locally
heavy possible, to portions of the Aleutians and eventually into
the Panhandle and southern Alaska by the end of next weekend.
Above normal temperatures on Day 4 across the majority of the
state should transition to near or below normal by the end of the
week and into next weekend. Upper level ridging begins to build
back across the southern half of the state by Day 7-8, so another
warm up can be expected across the Aleutians and the southern
third to half of the state while well below normal temperatures
are possible across northern Alaska underneath of persistent upper
level troughing.

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