Alaska Extended Forecast Discussion NWS Weather Prediction Center College Park MD 323 PM EDT Fri Mar 22 2019 Valid 12Z Tue Mar 26 2019 - 12Z Sat Mar 30 2019 The most common theme in today's guidance is for a strong upper ridge over mainland Alaska/Gulf of Alaska and Yukon to become more suppressed toward days 7-8 Fri-Sat while another ridge builds into the western mainland and over/north of Siberia. There is also decent consensus toward a deep trough settling over the far western Pacific with an embedded upper low near Kamchatka. The most prominent question marks involve how quickly the initial ridge aloft drops southward, and related very uncertain details of flow ahead of the developing western Pacific trough and continuing around the initial ridge. A deep storm reaching the far northwestern Bering Sea at the start of Tue will push a dying front into the western mainland early in the period with mostly light accompanying precipitation (versus some heavier activity just before 12Z Tue). Beyond that feature one or more shortwaves aloft may produce light/scattered precipitation but with low confidence in specifics. The Tue-Wed portion of the forecast reflects an operational model blend of the 00Z GFS/ECMWF/UKMET. Ensemble means have been trending stronger with the upper ridge over the past 1-2 days, adding support for this model cluster versus the weaker CMC or 06-12Z GFS runs. The ECMWF mean has been leading the GEFS mean for the stronger trend. Although the ridge has trended stronger there is somewhat of a southward trend for the upper high center. Confidence is quite low in details of shortwave energy across the Aleutians/Bering Sea and around the initial ridge. By Thu the GFS runs are on the faster side of the spread with the GEFS means considerably toning down the shortwave which GFS runs bring into the Bering at that time. Meanwhile by Fri-Sat the 00Z ECMWF becomes rather amplified with its shortwave over the mainland and Yukon. By late week/early weekend the ensemble means show better than average agreement in depicting the western Pacific trough anchored by an upper low near Kamchatka and the ridge building over and northwest from the western mainland. Like earlier in the period, the ECMWF mean is stronger with the ridge than recent GEFS means with a gradually stronger trend over the past couple days. The 00Z CMC mean also forecasts a strong ridge Fri-Sat. Thus preferences lean more to the ECMWF mean late in the period with some NAEFS also included to account for the CMC mean. Above considerations Thu-Sat lead to the early period model blend transitioning toward increasing ensemble mean weight, reaching 100 percent by day 8 Sat. Rausch Bullet points from the WPC Days 3-7 Hazards chart can be found at: https://www.wpc.ncep.noaa.gov/threats/threats.php - High winds across portions of the Aleutians, Mon, Mar 25. - Much above normal temperatures across portions of mainland Alaska, Tue-Wed, Mar 26-Mar 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