Alaska Extended Forecast Discussion NWS Weather Prediction Center College Park MD 529 PM EST Thu Dec 23 2021 Valid 12Z Mon Dec 27 2021 - 12Z Fri Dec 31 2021 ...Overview... The block pattern with the large upper ridge and surface high over the northeast Pacific early in the week is expected to gradually weaken and settle southward by the middle to end of the week. This will result in the transition from an amplified to a more quasi-zonal flow pattern by the end of the forecast period. Multiple shortwaves and low pressure systems from the Bering and the Aleutians will likely bring a few rounds of snow for much of the mainland. ...Overview and Guidance Evaluation... The 12Z model guidance suite remains in excellent overall agreement on the dominant upper ridge situated over the North Pacific near 45N/155W through early next week, and then shifting southward by mid-week and beyond as a more energetic storm track from eastern Siberia begins eroding the ridge. The UKMET is stronger with both the storm system tracking across the state Sunday night and also with the system approaching from the Bering on Wednesday, although the positions look reasonable. By Thursday and Friday, the 12Z GFS is considerably stronger with the ridge across the Aleutians and Gulf region and loses support from its ensemble mean, whereas the CMC/ECMWF agree on a more suppressed ridge with more shortwave energy tracking eastward across southern Alaska and the Aleutians. Taking these factors into account, a GFS/ECMWF/CMC blend was used through mid-week, and increased use of the ensemble means while retaining some of the CMC/ECMWF along with some previous WPC continuity to close out the week. ...Weather/Hazard Highlights... Multiple rounds of snow are likely across central and northern portions of the mainland through the middle of the week, with the greatest potential for this late Tuesday and into early Tuesday. Some locations across the Interior may become warm enough for a mix of rain/snow or even plain rain in the warm sector of the low. Farther south across the Aleutians and extending eastward to the Kenai Peninsula, more rain/snow showers will be possible for the end of the week, although specifics are unclear on timing and magnitude at this time. In terms of temperatures, the greatest cold anomalies are expected across the southeast Panhandle region early in the week, with an arctic air mass entrenched over the Yukon and British Columbia yielding highs at least 15-20 degrees below normal. Elsewhere across the state, widespread above average temperatures are likely for the Interior and extending north of the Brooks Range, with the potential for a few record highs. Hamrick Hazards: - Heavy snow across portions of mainland Alaska, Sun, Dec 26 and Tue, Dec 28. - Much below normal temperatures across portions of the Alaska Panhandle, Sun-Tue, Dec 26-Dec 28. Additional 3-7 Day Hazard Information can be found on the WPC medium range hazards outlook 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