Alaska Extended Forecast Discussion NWS Weather Prediction Center College Park MD 309 PM EST Wed Mar 06 2019 Valid 12Z Sun Mar 10 2019 - 12Z Thu Mar 14 2019 The models and ensemble means show better than average agreement and continuity for the overall pattern during the days 4-8 period (Sun-Thu). A strong but gradually weakening system near the western coast of the mainland will establish a mean trough aloft over 160-170W longitude. Trailing Aleutians/North Pacific trough energy should take on a negative tilt by midweek with a closed or nearly closed low possibly reaching near Kodiak Island by next Thu. Farther north an Arctic upper low tracking along 80N latitude should briefly extend a trough southwestward into the North Slope region by early next week. Expect the high latitude trough to retreat Wed-Thu as a western Canada into mainland Alaska ridge builds ahead of the aforementioned negatively tilted trough. The most prominent focus for precipitation during the period will be along the southern coast and Panhandle while a couple episodes of strong winds will be possible across and near the North Pacific. Aside from minor detail and timing differences, the majority cluster of guidance (00Z GFS/ECMWF/CMC and 06Z FV3 GFS) is consistent and similar for significant features during the first half of the period. Thus those models served as the basis for the forecast early in the period. The 06Z GFS has some alternative details for the strong Bering system nearing the southwestern part of the mainland. Late arrival of the 12Z GFS prevented its consideration for the forecast. Model consensus has also been consistent for the system tracking along the Aleutians by Mon though there is a hint of a slightly slower trend by Tue. The ensemble means are starting to show better definition but not yet quite to the level of an operational model average. During the latter half of the period there is still a fair degree of uncertainty over the exact evolution of upper trough energy over/south of the Alaska Peninsula by Tue-Wed and how much interaction may occur with the initially established trough to the north--leading to differences in surface low track among the guidance. The overall average of guidance for surface low pressure has changed little over the past 24 hours. The ECMWF mean is closest to the middle of the envelope and continuity with a track just east of Kodiak Island by early Thu. The past couple ECMWF runs are farther east while GFS runs have been waffling between tracks to the east of Kodiak Island and farther southwest like most GEFS mean runs thus far. An early look at the new 12Z ECMWF reveals a track slightly west of the 00Z ECMWF mean. Based on guidance through the 06Z cycle the preference is for an intermediate approach that is closest to the ECMWF mean in principle. There is still considerable spread for details along and south of the Aleutians during Tue-Thu. The most common theme is for a progressive wave to track south of the Aleutians Wed into Thu, with the ensemble means suggesting a hint of a feature in the vicinity of operational runs. The 00Z CMC is faster and northward of most other solutions. A blend approach provides a reasonable starting point for the high latitude upper high and trailing Arctic trough. There is still some question over exactly what happens to the far southwest periphery of the trough by midweek with minimal confidence in a specific solution due to its small scale. At the surface expect a front to settle toward the central part of the mainland as high pressure extends farther eastward across the Arctic. The typical increase of detail uncertainty and desire to maintain continuity near the Gulf of Alaska favored incorporation of the 00Z ECMWF mean and 06Z GEFS means during the latter half of the period, reaching 50-60 percent total weight by days 7-8 Wed-Thu while holding onto some components of the 06Z FV3 GFS/00Z ECMWF. Rausch Bullet points from the WPC Days 3-7 Hazards chart: https://www.wpc.ncep.noaa.gov/threats/threats.php - Heavy precipitation across portions of the Alaska Panhandle and mainland Alaska, Sun-Tue, Mar 10-Mar 12. - High winds across portions of the Alaska Panhandle and mainland Alaska, Sun-Mon, Mar 10-Mar 11, and Wed, Mar 13. - High winds across portions of mainland Alaska, Sat-Sun, Mar 9-Mar 10. - High winds across portions of the Aleutians, Sat-Mon, Mar 9-Mar 11. WPC medium range Alaskan products including 500mb, surface fronts/pressures progs and sensible weather grids can 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