Alaska Extended Forecast Discussion NWS Weather Prediction Center College Park MD 543 PM EDT Wed Apr 07 2021 Valid 12Z Sun Apr 11 2021 - 12Z Thu Apr 15 2021 ***Atmospheric river event likely early next week*** ...Guidance/Uncertainty Assessment... The latest models and ensembles are in relatively good synoptic scale agreement through most of the 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. A shallow ridge is expected to build across the mainland and western Canada through early in the week, while an upper trough becomes established over the northern Gulf. Similar to yesterday, recent runs of the ECMWF/CMC/JMA remain better aligned with ensembles than the GFS, which is stronger with shortwave energy across the Aleutians/Gulf region. The UKMET was also less favored given a westward displacement with the main surface low over the Bering as early as Monday. Accordingly, the WPC Alaskan product suite was primarily derived from a blend of the 12Z GFS/ECMWF/CMC/WPC continuity through Tuesday, and some of the 12Z ECMWF/CMC and the GEFS/ECMWF ensemble means for mid next week amid growing forecast spread. ...Weather/Hazards Highlights... Temperatures across much of the Alaska domain should still be quite cold going into Sunday with an Arctic surface high governing the weather pattern over the weekend. The good news is a steady moderation trend is forecast going forward into next weekend as this 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 Wednesday and Thursday. 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 up to six inches of QPF across windward facing terrain, and one or more atmospheric rivers could set up and result in some 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 Monday-Thursday time period. Moderate to heavy snow is also becoming more likely for portions of the Interior next weekend owing to warm air advection. Hamrick Hazards: - Heavy precipitation across portions of the Alaska Panhandle and mainland Alaska, Mon-Wed, Apr 12-Apr 14. - Much below normal temperatures across portions of mainland Alaska, Sat-Sun, Apr 10-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