Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
258 PM EDT Thu Aug 23 2018

Valid 12Z Mon Aug 27 2018 - 12Z Fri Aug 31 2018

The extratropical transition/interaction between current Tropical
Cyclones Cimaron and Soulik are wreaking havoc with the medium
range forecast for the high latitudes of the North Pacific region.
The models/ensembles are torn between which cyclone to reamplify
as a cold core system through the westerlies before lifting
through the Bering Sea next week. The ensemble means, taken
verbatim, could not separate the two camps of solutions which was
also muddied by potential northern stream merging of an upper low
across northeastern Russia (Chukchi peninsula/Gulf of Anadyr) as
ex-Cimaron/Soulik race across the Dateline. It seemed that the
deterministic solutions most like continuity and like the slim
majority of guidance that preferentially develop ex-Soulik (the
farther east system) before transitioning back to ex-Cimaron via
the northern stream interaction were the 00Z ECMWF/Canadian and
06Z GFS (somewhat). Followed that grouping with some modest
influence of the 00Z ECMWF ensemble mean for uncertainty which at
least was close to continuity. This would take the infused system
across the Aleutians early Wednesday then into SW Alaska Thursday
and perhaps into the Gulf next Friday, but with low confidence in
how this all will unfold. Precluded from this, of course, is
neither option A or B but C -- none of the above (see 12Z
UKMET/Canadian).

Rather wet pattern for the Aleutians across Southcentral as the
main low pushes through the region, but at least a brief dry
period early in the week with weakening high pressure ahead of the
main low. Temperatures will be within several degrees of average
but with mild overnight lows along the southern coast as the warm
front lifts across the Aleutians/AkPen.

Fracasso


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