Alaska Extended Forecast Discussion NWS Weather Prediction Center College Park MD 645 PM EST Tue Mar 09 2021 Valid 12Z Sat Mar 13 2021 - 12Z Wed Mar 17 2021 ...Overview and Guidance/Uncertainty Assessment... Today's guidance provides added trends toward a more blocky pattern with time. Expect a sharpening upper ridge reaching the mainland by the start of the weekend to split off a closed high that remains in the Arctic for a while next week. At the same time an elongated closed low over the northeastern Pacific will likely approach the Panhandle and then lift northward before either departing or shearing out underneath the upper high. Meanwhile an upper trough that crosses the Bering Sea and Aleutians during the weekend should elongate across the eastern Bering/Alaska Peninsula by early Monday, possibly forming a closed low soon thereafter. Then digging flow on the western side of the overall trough should pull the upper low farther south into the Pacific by the middle of next week. From the weekend into the start of next week, the 12Z GFS/CMC and 12Z/00Z ECMWF provided the best clustering in principle for meaningful large scale features. Confidence is below average for the specifics of surface low pressure that may track near or into the southern Panhandle ahead of the Northeast Pacific upper low, given significant detail spread in latest model runs and the relatively small scale of the system. This favors an intermediate approach for now. Farther west there is decent agreement among most models/means that a strong system over the far northwestern Bering Sea will anchor a front that crosses the eastern Bering, with a triple point wave likely breaking off near the Alaska Peninsula around Sunday into early Monday. By days 7-8 Tuesday-Wednesday the ensemble means have been fairly consistent in advertising some troughing from the mainland into the Pacific but with ambiguity in the specifics. Operational GFS/ECMWF runs fit within that general template though unsurprisingly with greater spread for various aspects of one or more streams. The 12Z model/mean cycle suggests a more coherent trend/clustering toward having an upper low drop south or southeast of the Alaska Peninsula by midweek while a weakness persists over the mainland. Individual models still vary with the ultimate evolution/track of the wave that forms near the Alaska Peninsula as well as one or more other surface lows. Thus by this time frame the forecast blend incorporated some 12Z GEFS/00Z ECMWF mean input. As for operational solutions, both ECMWF runs were reasonable blend components through the end of the period. The 12Z GFS became flatter than consensus with North Pacific flow by next Wednesday, favoring introduction of the parallel GFS to some degree. Finally the blend phased out the CMC late due to northern stream details beginning to differ from consensus. ...Weather/Hazards Highlights... The developing system that may track into or near the southern Panhandle this weekend may bring some moderate to heavy precipitation to locations in its vicinity. At this time confidence is lower than desired for exact details of this system. Meanwhile a front crossing the eastern Bering Sea and Aleutians early in the weekend will be accompanied by brisk to strong winds and a precipitation shield that should extend into the far western mainland. Then a triple point wave near the Alaska Peninsula should bring more precipitation focus to the northern Peninsula and southwestern mainland while the leading front will likely extend moisture into the southeastern coast and Panhandle. Some precipitation could linger along the southern coast through the first half of the week depending on the specifics of the aforementioned wave and one or more other lows. Expect unsettled conditions to persist over the Aleutians for a number of days. The North Slope will see above to well above normal temperatures through the period with highest anomalies most likely around Sunday-Monday. Farther south the weekend will start out on the cold side with below to well below normal readings except for perhaps far western locations. After Saturday there will be a warming trend from west to east as high pressure departs into Canada. By Monday most below normal temperatures should be confined to parts of Southcentral as well as the Panhandle which should be colder than average through the forecast period. Rausch Hazards: - Heavy snow across portions of the Alaska Panhandle, Fri-Sat, Mar 12-Mar 13. - High winds across portions of the Aleutians, Sat, Mar 13. 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