Alaska Extended Forecast Discussion NWS Weather Prediction Center College Park MD 302 PM EDT Mon Aug 26 2019 Valid 12Z Fri Aug 30 2019 - 12Z Tue Sep 03 2019 A robust system will push across the Aleutians and through the eastern Bering Sea late Saturday into early next week as upper ridging over the eastern mainland slips eastward into Canada. The models had wavered on if this potential system would actually come together, and while there remains notable spread in the ensembles, the ensemble trend and recent deterministic runs warranted re-introducing a deeper system into the forecast. However, did not indicate a strength much below the ensemble means and weaker deterministic models around 990mb rather than the 970s mb per some guidance. Lead weaker system will move across the AKPen and dissipate Friday ahead of the deeper system. To the north, models still disagree on how to rotate a shortwave around the main arctic upper low near the Queen Elizabeth Islands--either westward toward Wrangel Island, eastward along the coast, or just meander north of the Bering Strait. Regardless, lead upper low will overtake that smaller feature if in its way, only to then be overtaken by the larger system on its heels. Blend between the 12Z GFS and 00Z Canadian/ECMWF offered a good starting point, then trending toward the more western and weaker Canadian by next Sun/Mon along with a majority ensemble weighting (06Z GEFS/00Z ECMWF ensemble mean) before then just relying on the ensemble means as their agreement was better than average out to next Tuesday. This would take the system northward along the western coast as the front slows into the Gulf. This could set up quite a wet pattern for portions of Southcentral in favored non-sheltered areas (southern AKPen/Kodiak/Kenai into PWS). Several inches of rain may be possible over several days as the system moves through. Fracasso 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 - Heavy rain across portions of southern Alaska, Sun-Mon, Sep 1-Sep 2. - Heavy rain across the central Aleutians, Sat, Aug 31. 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