Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
406 PM EDT Thu Sep 6 2018

Valid 12Z Mon Sep 10 2018 - 12Z Fri Sep 14 2018

...Guidance/Uncertainty Assessment...

An impressive mid to upper-level ridge becomes established over
the eastern Bering Sea, partially in response to the extratropical
remains of what was Typhoon Jebi. This upper high will remain a
dominant feature in the forecast for much of the forecast period. 
This resembles an omega block pattern with an upper low and
attendant surface low south of the Aleutians, and another upper
low near the British Columbia coast.  This configuration should
remain in place through early next week before upstream height
falls from eastern Siberian approach the mean ridge axis.
Ultimately this will force the synoptic-scale pattern eastward
allowing for the ridge to set up over mainland Alaska by the
middle of next week.

The overall guidance has a reasonable handle on the evolution of
the forecast through early next week. The process of pushing the
ridge downstream remains somewhat in question as a few operational
models attempt to squash the northern extent of the ridge.  Given
the amplified flow pattern, a multi-model consensus of the 12Z GFS
and 00Z CMC/ECMWF was incorporated through Day 6 and then a more
ensemble mean influenced forecast for the end of next week.


...Weather Highlights/Hazards...

The beginning of the forecast period is forecast to be mainly dry
with mostly sunny skies across much of the mainland, owing to the
large mid-upper level ridge in place.  Rainfall prospects increase
by Wednesday for the Aleutians as the deep low over the northern
Pacific tracks closer to the region, and then reaching western
Alaska by the end of the week.  Temperatures are expected to be
mild for most inland locations, with 60s for highs and 30s/40s for
lows. 

D. Hamrick


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