Alaska Extended Forecast Discussion NWS Weather Prediction Center College Park MD 608 PM EST Thu Feb 20 2020 Valid 12Z Mon Feb 24 2020 - 12Z Fri Feb 28 2020 The large scale flow pattern across Alaska and the North Pacific will undergo some degree of modulation during the extended forecast period, transitioning from a relatively progressive pattern to one with at least some degree of (relatively weak) blocking. Increased atmospheric blocking around the northern hemisphere next week is expected to result in a relatively strong positive height anomaly center across northeast Asia, and a negative height anomaly center across northern Europe. Teleconnections associated with both of these strong hemispheric anomalies support development and persistence of a mean upper-level trough across the Aleutians/Bering Sea, and some degree of ridging across western Canada. Ensembles show this general idea heading into next week, despite quite a bit of variability on the details of individual low pressure systems. The 12Z ECMWF was heavily used as a basis for the forecast during days 4-5 (Mon-Tie), as this solution showed relatively good consensus with the consensus of guidance and ensemble means. As upper-level ridging begins to build by Mon, heights should briefly rise across the Alaska Panhandle and portions of mainland Alaska before the ridge axis shifts east into its favored position across western Canada and the aforementioned mean trough/upper low sets up across the Aleutians. A low pressure system is forecast to approach southern mainland Alaska Tue-Wed, bringing a round of potentially heavy precipitation and high winds, with another similar system perhaps approaching by Thu-Fri. Deterministic solutions continue to struggle with the evolution of the upper ridge next week. A trend was noted among the 12Z guidance toward pinching off a portion of the ridge into a closed upper-level high across the northern Bering Sea by Tue. Farther east, variability remains on how quickly the ridge axis across western Canada/Southeast Alaska breaks down, although a consensus of ensembles suggests this should occur by later next week, Thu or Fri. Rapidly increasing spread among deterministic solutions by the middle of next week with respect to the track/intensity of individual low pressure systems warranted increasingly heavy use of ECENS/GEFS ensemble means during the day 6-8 (Wed-Fri) time period. Ryan 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 Hazards: - Heavy precipitation across portions of the Alaska Panhandle and mainland Alaska, Tue-Thu, Feb 25-Feb 27. - High winds across portions of mainland Alaska and the Aleutians, Mon-Tue, Feb 24-Feb 25. 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