Alaska Extended Forecast Discussion NWS Weather Prediction Center College Park MD 610 PM EST Thu Jan 30 2020 Valid 12Z Mon Feb 03 2020 - 12Z Fri Feb 07 2020 The majority of guidance agrees fairly well for the large scale pattern evolution during the days 4-8 Mon-Fri period. Arctic upper trough/low energy should gradually settle toward a position just west of the northern mainland, while the combination of a couple features aloft will support deep low pressure over the Aleutians/Bering Sea followed by steady weakening as the system eventually heads inland. Fast northern Pacific flow will carry along multiple features that have less consensus in the guidance though there is a decent signal for a better defined western Pacific system coming into the picture toward the western Aleutians late next week. Over recent runs there have been some notable differences/trends in specifics of Arctic flow. ECMWF mean runs through 00Z had been trending toward fairly quick movement of an initial upper low to a position just west of the mainland--with the operational 00Z ECMWF, 00Z/12Z UKMET, and 12Z CMC mean generally supporting that idea. On the other hand GFS/GEFS runs have been holding the initial upper low farther east while using flow to its west to dig the trough/embedded low into the consensus late-week position. 12Z ECMWF adjustment delayed the timing of the evolution, ultimately favoring a model blend (00Z/12Z ECMWF and 12Z GFS/UKMET) followed by a model/mean blend (00Z ECMWF mean/12Z GEFS for the ensembles) for a single deterministic forecast. The 12Z ECMWF mean trended close to this blend approach. The aforementioned model blend also provides the best starting point for resolving differences with the strong Aleutians/Bering Sea system. There are multiple influences on system specifics, including at least two individual upper features as well as details of flow to the north. Consensus surface low track is farther north than continuity and the past couple ECMWF mean runs through the 00Z cycle, with the 12Z ECMWF mean adjusting toward latest preference. Across the North Pacific domain there is a hint of a leading system reaching into the Gulf of Alaska by around early Tue, followed by a front extending south from the Bering Sea storm. An upstream wave may brush the Aleutians around Wed-Thu, though after Wed models/ensembles diverge enough to recommend only a modest reflection until better agreement develops. Another trailing feature could reach the western Aleutians as well. Models and means show a larger scale upper trough reaching the western Pacific late in the week so there is a somewhat better signal for low pressure reaching near the western Aleutians by day 8 Fri. The overall pattern will likely support highest precipitation totals from just east of the Kenai Peninsula through the Panhandle, with lesser amounts extending west through the Aleutians. The strong system initially over the Aleutians/Bering Sea and then weakening as it eventually heads into the mainland, plus interaction with a leading stationary front, should produce meaningful precipitation over portions of the southern and western mainland. Rausch 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 mainland Alaska, Sun, Feb 2. - Heavy precipitation across portions of the Alaska Panhandle and mainland Alaska, Mon-Thu, Feb 3-Feb 6. - Much below normal temperatures across portions of mainland Alaska, Sun, Feb 2. - Much below normal temperatures across portions of mainland Alaska, Sun-Mon, Feb 2-Feb 3. - High significant wave heights for coastal portions of mainland Alaska and the Aleutians, Sun-Mon, Feb 2-Feb 3. 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