Alaska Extended Forecast Discussion NWS Weather Prediction Center College Park MD 255 PM EDT Fri Aug 23 2019 Valid 12Z Tue Aug 27 2019 - 12Z Sat Aug 31 2019 Upper level ridging will shift into British Columbia as the medium range period (Tues - Sat) begins, favoring stretched troughing from the Gulf of Alaska south-southwestward into the Pacific and a couple of weak surface low pressure areas moving along the main baroclinic zone. Initial troughing along the Gulf Coast eventually shifts inland, being replaced by upper level ridging as some kind of organized system sinks south of about 50N in the Pacific. Models today show better agreement than previous days, as previous runs of the GFS had been advertising a stronger/more coherent low pressure south of the Aleutians rather than a more stretched trough as is the consensus today. Elsewhere across Alaska, a main upper low meanders east/northward as a possible shortwave rotates around it through the North Slope region. The ECMWF continues to show a stronger representation of that idea, and while plausible, a blend with the other guidance suppressed its depth given continued uncertainty. In the Bering Sea, high pressure dominates in the beginning of the period before a system moves eastward along the Aleutians. Models also show relatively good agreement on this system being reinforced by rotating shortwaves, but continuing to show a slow buy steady movement eastward into next weekend. The blend today features a majority deterministic model blend for days 4-5 (between the 00z ECMWF/12z GFS/00z CMC), with increasing weighting of the ensemble means (ECENS/GEFS) from day 6 onward. This mitigates any normal amplitude/timing differences and also presents a forecast very close to yesterdays continuity. In terms of sensible weather, a weakening system in the Gulf will continue the threat for heavy rains across portions of the Panhandle on Tuesday, with conditions likely to mostly dry out the rest of the week. Scattered to locally heavy rain/snow possible across the North Slope with the passage of a cold front, while the next system in the Aleutians spreads rain from the western Aleutians to the Peninsula late next week and into the weekend. Santorelli 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 the southern portion of the Alaska Panhandle, Tue, Aug 27. 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