Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
312 PM EDT Tue Sep 04 2018

Valid 12Z Sat Sep 08 2018 - 12Z Wed Sep 12 2018

...Guidance/Uncertainty Assessment...

Model and ensemble forecasts cluster well this weekend and a
composite blend of the latest GFS/ECMWF and GEFS/ECMWF ensemble
means offers a great starting point in an amplified flow pattern
with above average predictability. Forecast spread and uncertainty
gradually increases into next week with the ECMWF/ECMWF ensembles
offering even more amplified flow than the GFS/GEFS. Prefer to
lean WPC composite weighting in favor of the more amplified
solution given lead-in flow amplitude and some trend toward
amplification between the 06 and 12 UTC GEFS ensembles.

...Weather Highlights/Hazards...

Guidance shows a highly amplified cutoff pattern as an omega block
forms over the northern Pacific with the northern jet stream going
over the top of the Bering Sea ridge into the Arctic Ocean before
digging back down through Alaska in an unsettled/cooling pattern.
The Bering Sea centered closed ridge builds robustly in partial
response to the lifting on its western periphery into the far high
latitudes the extratropical low associated with former western
Pacific typhoon Jebi. As part of the block underneath, stormy
closed mean lows linger and are periodically reinforced to the
south of the western Aleutians and as per the digging northern
stream flow down across the state over the Gulf of Alaska.

Schichtel

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