Alaska Extended Forecast Discussion NWS Weather Prediction Center College Park MD 306 PM EDT Sat Aug 10 2019 Valid 12Z Wed Aug 14 2019 - 12Z Sun Aug 18 2019 Today's guidance continues to show an increasingly amplified/blocky pattern taking shape after midweek. Most models/ensemble means have furthered recent trends toward a stronger North Pacific ridge aloft building into the eastern/northern Bering Sea. This ridge should support a deepening upper trough over northwestern Canada into the northeastern Pacific while keeping low pressure to the southwest of the Aleutians (in contrast to earlier days when the system was expected to reach the western Aleutians or even the Bering Sea). Confidence remains low regarding specifics of short range Arctic energy. There is relative consensus among the 00-06Z models and 12Z GFS that a compact feature should be just off the northwest coast of the mainland as of 12Z Wed. However soon after that time solutions diverge for timing and exact path as it feeds into the developing mean trough. At the time of forecast preparation a modest majority and recent trends favor leaning partially in the slower 00Z ECMWF/CMC direction versus faster GFS runs (06Z run a bit slower than the 00/12Z versions). Not surprisingly the remaining 12Z models have made some adjustments, primarily with slightly faster timing to or toward the GFS. Trends also show more amplified troughing to the southwest of the feature as it continues inland. In the wake of this low/trough there are further question marks with upstream Arctic flow as well as path of the upper low that starts the period near the western Canadian Archipelago (00Z ECMWF/CMC both dropping the upper low into the Yukon versus GFS runs keeping it well northward). The ensemble means support an intermediate solution, to which the 12Z ECMWF/CMC have adjusted. Interestingly, even with the various detail differences the 06Z GFS and 00Z ECMWF/CMC end up with fairly similar solutions over the mainland and northeastern Pacific around day 7 Sat. A blend of the 00Z ECMWF/06Z GFS/00Z CMC provided a good starting point to represent detail and forecast preferences early in the period, days 4-5 Wed-Thu. For the rest of the forecast the various detail discrepancies in operational runs warranted a gradual increase of 06Z GEFS and 00Z NAEFS/ECMWF mean input--but only up to about 50 percent total weight by day 8 Sun as the more agreeable aspects of the models offered some detail enhancement relative to the means alone. Separate frontal systems affecting the northern and southern mainland may produce some areas of enhanced precipitation during the first half of the period. Exact duration will depend on timing of shortwave energy dropping southeastward across the mainland. The system over the western Pacific should still extend an area of fairly strong winds and one or more bands of significant rainfall into the Aleutians but with less eastward extent than forecast in prior days. Rausch 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 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