Alaska Extended Forecast Discussion NWS Weather Prediction Center College Park MD 752 PM EDT Sat Oct 22 2022 Valid 12Z Wed Oct 26 2022 - 12Z Sun Oct 30 2022 ...A Bering Sea low will bring a threat of high winds and waves to the Aleutians early to middle of next week with locally heavy snow possible for inland western Alaska midweek... ...Heavy mountain snows and coastal rain threat across the Alaska Panhandle into southern coastal sections late next week... ...Overview... Guidance shows a progressive and energetic pattern with generally westerly flow to the south of a mean upper low likely to prevail over and possibly extending northwest from the mainland. An upper ridge over the Arctic should hold this mean low in place for most of the period. There will likely be two primary systems of note within the active pattern. The first should reach the southwestern mainland by early Wednesday with a leading wave over the Gulf of Alaska ultimately becoming the primary low soon thereafter. The ensemble means and some models show another potentially significant system tracking into the Bering Sea and then the Gulf late week into next weekend. The most confident effects from these systems will be a threat for significant precipitation along the Panhandle and parts of the southeastern coast, as well as for winds/precipitation over and southwest of the mainland midweek with the first low. Confidence is lower for details with the second system, especially west of the Panhandle. ...Guidance/Predictability Assessment and Preferences... For the most part the guidance has come into good agreement for the initial system whose parent low should be over or near the southwestern mainland as of early Wednesday, with a leading Gulf wave already beginning to take shape and quickly becoming the dominant system that should linger just off the southeastern coast/Panhandle into Friday. The main difference of note is that latest GFS runs are on the deep/western side of the guidance spread for the parent low as of 12Z Wednesday. Multi-run trends show that the GFS has already trended significantly to the ECMWF cluster for latitude over the past couple days (versus a farther north track), so will monitor to see if the GFS continues to trend in the ECMWF direction. The preferred forecast blend incorporated three-fourths total weight of the ECMWF/UKMET/CMC cluster. Guidance spread and run-to-run variability yield significantly lower confidence for the next system that could reach the Bering Sea or vicinity by around late week. Dependence on details of separate streams, one emerging from eastern Asia and a separate one that contains an initial western Pacific shortwave, also suggests fairly low predictability at this time. The latest ensemble means are showing some improved definition for this system over the Bering around Friday with agreeable subsequent emphasis shifting into the Gulf by next weekend. Meanwhile operational models differ widely, with the 12Z/18Z runs trending toward a faster northern stream/slower southern stream to yield a split of features. The 06Z GFS was still somewhat suppressed with its primary wave but closer to the means in principle. On the other hand the 12Z ECMWF/CMC become slowest and strongest with the Bering low versus the 00Z ECMWF that was closer to the timing of the means. On the positive side, these divergent solutions do get closer together by the end of the period. Available guidance through the 12Z cycle, combined with the uncertainty of the forecast, favored trending the forecast toward the 12Z GEFS/00Z ECMWF means and 00Z ECMWF/06Z GFS by next Saturday-Sunday to maintain decent continuity aside from a moderately slower trend. The new 12Z ECMWF mean is close to the operational 00Z ECMWF evolution. As was the case for the leading system described above, the forecast over higher latitudes has seen a trend of the GFS/GEFS toward the ECMWF/ECMWF mean over the past couple days. The currently improved consensus has an upper ridge/high persisting around 75-80N latitude for most of the period while mid-late week energy to its south may retrograde across the North Slope and then settle over or near the northwestern mainland. A general model/mean blend represents consensus well and accounts for typical detail uncertainty. ...Weather/Hazards Highlights... Flow behind the leading storm forecast to move onshore into southwestern Alaska by early Wednesday should support strong winds and waves across the Aleutians into the Alaska Peninsula through midweek. Meanwhile inland sections of southwestern Alaska may see locally heavy snow continue from the short range time frame into Wednesday. Leading Gulf of Alaska development and then persistence of this low, along with associated moisture, will likely support an episode of heavy rain and higher elevation snow across the Panhandle and parts of the southeastern coast during the latter half of the week. Confidence is much lower for the details regarding a trailing system that may affect the Aleutians/Bering Sea late this week and locations near the Gulf next weekend. Possible solutions Friday-Saturday range from mere cyclonic flow and light precipitation over the Bering Sea to a strong system that would produce a more significant wind/wave threat, with various scenarios in-between as well. There is a somewhat better signal for low pressure to reach the Gulf at some point next weekend, leading to another period of enhanced precipitation along the Panhandle and possibly the southern coast. Locations seeing significant totals from the mid-late week event may be sensitive to any additional activity from next weekend's potential event. Expect temperatures to be mostly above normal over the west and below normal over the east/Panhandle at the start of the period Wednesday. Then the pattern evolution should support expanding coverage of below normal temperatures, especially for highs, with the greatest anomalies to be over southern areas. Low temperature anomalies will likely be more mixed though with increasing tendency for below normal readings over the south and parts of the west and above normal lows hanging on over the North Slope. Rausch 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