Alaska Extended Forecast Discussion NWS Weather Prediction Center College Park MD 304 PM EST Fri Mar 08 2019 Valid 12Z Tue Mar 12 2019 - 12Z Sat Mar 16 2019 Predictability across Alaska is slightly above average during the early portion of the extended period (Tue-Wed), and near to slightly below average by the latter portion of the period. Confidence is relatively good with respect to the large scale flow pattern across the region, with continued mean upper-level troughing near the Aleutians, and an upper ridge axis rebuilding across western/northwestern Canada. 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 weak lead surface low moving from the Gulf into the Alaska Peninsula on day 4 (Tue) and then a much stronger low pressure system entering the Gulf Wed and then moving onshore in the Alaska Peninsula or southern mainland Alaska by Thu. By later Thu this system should weaken as it moves inland and merges with a broader area of shortwave energy. The forecast during days 3-4 was based heavily on a blend of the ECMWF/GFS solutions, which showed relatively good consensus during this time frame, and maintained good forecast continuity. In the wake of this Wed-Thu system, the flow becomes a bit more chaotic, with a couple smaller scale shortwaves expected to skirt south of the Aleutians and eventually move into the Gulf. Models suggest some consolidation of shortwave energy into a closed low south of the Aleutians by next Fri-Sat, likely associated with another deep surface low. Additional uncertainty arises in the handling of arctic shortwave energy exiting eastern Siberia on Thu, and whether this amplifies across the Bering or remains confined to higher latitudes. Given the increased spread, the forecast was trended toward heavier ensemble mean (ECENS/GEFS) on day 6 (Thu), with majority ensemble means during days 7-8 (Fri-Sat). Ryan 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, Wed-Thu, Mar 13-Mar 14. - High winds across portions of the Alaska Panhandle and mainland Alaska, Wed-Thu, Mar 13-Mar 14. - High winds across portions of mainland Alaska, Mon, Mar 11. - High significant wave heights for coastal portions of the Alaska Panhandle and mainland Alaska, Wed-Thu, Mar 13-Mar 14. 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