Alaska Extended Forecast Discussion NWS Weather Prediction Center College Park MD 624 PM EDT Thu Apr 8 2021 Valid 12Z Mon Apr 12 2021 - 12Z Fri Apr 16 2021 ***Atmospheric river event likely early next week*** ...Guidance/Uncertainty Assessment... The latest models and ensembles are in relatively good synoptic scale agreement through the first half of the forecast period, with the greatest differences residing with individual shortwave perturbations pivoting around the main upper level low/trough over the eastern Bering and northern Gulf region. One of the main differences noted in the guidance is that the GEFS mean was more out of phase compared to the well clustered CMC and EC ensemble means beyond Tuesday across the Bering and Aleutians, and generally less amplified with the upper trough/closed low over the Gulf region. This also holds true for the operational GFS. The latest runs of the ECMWF/CMC/UKMET are in better overall agreement than the GFS, and therefore the WPC Alaskan product suite was primarily derived from a blend of the 12Z ECMWF/CMC/UKMET/WPC continuity through early Wednesday, and then mainly CMC/ECMWF/EC mean for mid to late next week amid growing forecast spread. ...Weather/Hazards Highlights... Temperatures across much of the Alaska domain should begin warming up compared to the winter-like readings in the short range period as the Arctic air mass retreats, and the negative temperature anomalies abate. The latest model guidance is suggesting a return to above normal readings across much of the central and northern portions of the state by the middle of the week. In the precipitation department, very heavy rain and mountain snow is expected to make weather headlines from the Kenai Peninsula to the southeast panhandle region. Multiple shortwave disturbances pivoting around a broad upper level gyre over the Fox Islands/eastern Bering will result in enhanced onshore flow across this region. The potential exists for 6+ inches of QPF across windward facing terrain, and one or more atmospheric rivers could set up and result in flooding of low lying areas near the coast. The higher elevations of the coastal mountain ranges could get hammered by several feet of snow during the Tuesday-Thursday time period. Hamrick Hazards: - Heavy precipitation across portions of the Alaska Panhandle and mainland Alaska, Sun-Wed, Apr 11-Apr 14. - Much below normal temperatures across portions of mainland Alaska, Sun, Apr 11. 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 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