Alaska Extended Forecast Discussion NWS Weather Prediction Center College Park MD 306 PM EDT Sun Mar 10 2019 Valid 12Z Thu Mar 14 2019 - 12Z Mon Mar 18 2019 Confidence is relatively good with respect to the large scale flow pattern across Alaska and the North Pacific during the extended period, with persistent mean upper-level troughing near the Aleutians, and an upper ridge axis rebuilding across western/northwestern Canada, into portions of mainland and Southeast Alaska by late in the period. ECENS and GEFS D+8 standardized anomalies provide strong support for the persistence of this large scale pattern, with maximum positive 500 hPa height anomalies centered over central British Columbia, and minimum negative anomalies centered between the Aleutians and Hawaii. This setup will keep the preferred storm track near/south of the Aleutians and into the Gulf of Alaska, with persistent southerly flow into Alaska. Models/ensemble members showed good clustering surrounding a low pressure system moving onshore near Kodiak Island or southern mainland Alaska by Thu. By Thu night-Fri this system should weaken as it moves inland and merges with a broader area of shortwave energy farther north. The forecast during days 4-5 was based heavily on a blend of the ECMWF/GFS solutions, which showed relatively good consensus during this early portion of the extended period. The flow continues to look a bit more chaotic in the wake of the initial Thu system, with a number of smaller scale shortwaves expected to traverse the north central Pacific upper trough and eventually move into the Gulf. The ECMWF/GFS along with their ensemble means show some consensus that another surface low should move north into the Gulf Fri night-Sat, with perhaps a triple point low development farther east across the Gulf on Sun, and finally another potentially deeper low pressure system following a similar track by Mon. Spread with respect to timing, intensity, and structure of these systems gradually increases through time, but model spread by the end of the period is perhaps slightly less than average. Nonetheless, the chaotic nature of the flow pattern with multiple smaller scale waves makes for the potential for a highly changeable forecast. Additional uncertainty continues to arise in the handling of a couple areas of arctic shortwave energy exiting eastern Siberia during the middle to latter portion of the week, and whether they amplify across the Bering Sea or remain confined closer to eastern Russia as a consolidated upper low. Given the increased spread, the forecast was trended toward heavier ensemble mean (ECENS/GEFS) starting on day 5 (Fri), with majority ensemble means during days 7-8 (Sun-Mon). Ryan Bullet points from the WPC Days 3-7 Hazards chart: 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 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