Alaska Extended Forecast Discussion NWS Weather Prediction Center College Park MD 639 PM EST Thu Dec 19 2019 Valid 12Z Mon Dec 23 2019 - 12Z Fri Dec 27 2019 ...Below average temperatures expected across parts of mainland Alaska into next week... ...A couple of potentially strong storms may track near the Aleutians, bringing precipitation and strong winds... ...Wet pattern along the southeastern coast/Panhandle... The guidance for today continue to show relatively good agreement to begin the medium range period on the larger scale flow, but significant differences remain on the smaller scale/less predictable details especially towards the end of next week. Upper troughing over the mainland should persist through much of the period, which would promote an extended period of below normal temperatures which the core of should shift slowly westward with time next week. To the south, the guidance continues to show a very active North Pacific/Aleutians stream that should include a series of shortwaves traversing near or south of the Aleutians. To begin the period on Monday, one low pressure system looks to cross the Panhandle into the Gulf with low pressure lingering through next week over the Gulf of Alaska. Models show fairly good agreement on this, though the ECMWF remains a bit south of the consensus on low placement. This would support a persistent focus for precipitation along the southeastern coast/Panhandle, with heavy precipitation potentially more likely early in the week. Behind this another system looks to pass south of the Aleutians on Tuesday with greater uncertainty on timing as it enters the Gulf/Northeast Pacific Wednesday and beyond. The GFS/ECMWF are better clustered than the CMC, but are still displaced south of the ensemble means with the low center. On Thursday, yet another potentially deep low pressure system approaches the western/central Aleutians, but the deterministic models show large uncertainties on placement and strength of this low for days 7 and 8. Depending on the exact track and intensities of varies lows, some precipitation and strong winds are possible for parts of the Aleutians next week. This cycle of the WPC guidance favors a mostly deterministic model blend for days 4-5 between the 12z GFS and the 12z ECMWF, with smaller contributions from the 00z ECENS mean and the 12z GEFS mean. For days 6-8, weighting of the ensemble means was increased significantly to account for continued uncertainty in the deterministic runs. Santorelli 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, Mon, Dec 23. - High winds across portions of the Aleutians, Sun-Mon, Dec 22-Dec 23and Tue-Wed, Dec 24-Dec 25. - Much below normal temperatures across portions of mainland Alaska, Sun-Mon, Dec 22-Dec 23. - High significant wave heights for coastal portions of mainland Alaska and the Aleutians, Sun-Mon, Dec 22-Dec 23. 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