Alaska Extended Forecast Discussion NWS Weather Prediction Center College Park MD 323 PM EDT Thu Aug 15 2019 Valid 12Z Mon Aug 19 2019 - 12Z Fri Aug 23 2019 A relatively extratropical strong surface low originating from Tropical Storm Krosa (currently in the vicinity of Japan) will be the most significant feature on the map for Alaska during the extended forecast period as it tracks along/near the Aleutian Chain and perhaps toward the Alaska Peninsula by late next week. The ECMWF appeared reasonably well-centered within the ensemble spread with respect to this system through much of the forecast period. Given the origin of the low (extratropical transition), have less uncertainty concerns than typical for going a bit deeper with the low (as shown by the deterministic guidance), particularly early in the forecast period. Farther east, a blocky pattern initially in place with an upper high over the Bering Sea and upper low over the eastern Gulf looks to break down, but the pattern remains somewhat amplified (as would be expected downstream of an extratropical transition), and by later next week there's some consensus on a broad upper trough extending across mainland Alaska. The North Slope will potentially be subject to flow off the Arctic in this setup, although solutions do differ as to exactly how much the upper high breaks down and/or migrates westward which introduces some degree of uncertainty in the flow at higher latitudes across Alaska. The WPC forecast was initially based heavily on the deterministic 00Z ECMWF, with a gradual shift to heavier weighting of ECENS/GEFS ensemble means through time. Ryan Additional 3-7 Day Hazard information can be found on the WPC medium range hazards chart at: https://www.wpc.ncep.noaa.gov/threats/threats.php No significant hazards are expected over Alaska during this forecast period. WPC medium range Alaskan products including 500mb, surface fronts/pressures progs and sensible weather grids can also be found at: https://www.wpc.ncep.noaa.gov/alaska/ak_5dayfcst500_wbg.gif https://www.wpc.ncep.noaa.gov/alaska/akmedr.shtml https://www.wpc.ncep.noaa.gov/alaska/ak_5km_gridsbody.html