Alaska Extended Forecast Discussion NWS Weather Prediction Center College Park MD 657 PM EST Thu Nov 09 2023 Valid 12Z Mon Nov 13 2023 - 12Z Fri Nov 17 2023 ...Two intense Bering Sea systems to bring a threat for high winds and increasing snowfall chances... ...Overview... Latest guidance for next week is showing a gradual transition from an energetic and progressive pattern toward a large scale mean trough aloft settling into position near or just west of the western coast of Mainland Alaska by next Friday. There is reasonably good agreement and continuity for a leading front crossing the mainland on Monday to develop a wave that tracks over the Gulf of Alaska and offshore the Panhandle into Tuesday. However latest guidance has developed a fair amount of spread for what may be a more impactful system that should track from the western Pacific through the Bering Sea and into the mainland, bringing a variety of hazardous weather conditions to areas from the Bering Sea/Aleutians into the southwestern half or so of the mainland. A triple point wave forecast to develop along the southern coast after midweek may also focus enhanced precipitation to areas east of the Kenai Peninsula into the Panhandle. ...Guidance Evaluation and Preferences... Latest operational runs look reasonable for the start of the forecast period on day 4 Monday, given good continuity/agreement for the front reaching the mainland and subsequent Gulf wave development into Tuesday. Then after what seemed to be a brief period of better agreement for the western Pacific through Bering Sea into mainland storm, latest operational model runs have become quite divergent and variable with important surface details. This behavior appears to correspond to what appears to be a lower predictability evolution involving progressive dynamics lifting up the east side of the large scale mean trough, with some potential for influence from upstream energy complicating the forecast. This leads to a host of possibilities for surface depiction between a deep and consolidated system (00Z ECMWF and faster 12Z UKMET/CMC) and farther south track of potentially two waves (12Z ECMWF/GFS, with the 00Z UKMET quite weak/fast/suppressed). Timing spread has also greatly increased, between recent GFS runs adjusting slower with their strongest wave versus ECMWF/CMC nudging faster. 12Z ECMWF specifics also lead to a much deeper Gulf of Alaska surface low by late Wednesday-Thursday versus other guidance. The ensemble means exhibit some north-south spread across the Bering Sea and into the mainland but on average are closer to continuity (ECens generally between the slightly south GEFS and farther north CMCens). This reflects a lower percentage of individual members taking the southern side of the operational model spread. The means agree well on a triple point wave setting up along the southern coast by Thursday-Friday, near or just east of the Kenai Peninsula, as the upper trough approaches. Operational runs differ with where individual surface waves may be over the Gulf and broader northeastern Pacific. Based on model consensus to start the period followed by the rapid spread of guidance for the primary system of interest, today's forecast started with the 12Z GFS/ECMWF/UKMET/CMC (with some 00Z ECMWF included to facilitate transition thereafter) on day 4 Monday and then quickly adjusted toward the ensemble means (12Z GEFS/CMCens and 00Z ECens) by mid-late week with some 00Z ECMWF included on days 6-7 Wednesday-Thursday since that model run was closest in principle to the means. This resulted in a Bering Sea into mainland low track similar to though a bit faster than continuity, while awaiting any more meaningful trends that can be followed with more confidence. ...Weather/Hazards Highlights... The leading front reaching the mainland by Monday will bring strong winds to some locations, especially the northwestern mainland which will be closest to the deep anchoring surface low just north of Siberia. Precipitation (mostly snow) will spread across the mainland as well. The frontal wave that quickly develops over and tracks southeast from the Gulf of Alaska Monday into Tuesday may bring a brief episode of light to moderate precipitation to the Panhandle. Confidence in exact sensible weather effects from the trailing Bering Sea into mainland system has decreased somewhat over the past day given model divergence for low evolution, track, and timing. However there is continued potential for areas of high winds over the Bering Sea/Aleutians and into the southwestern mainland, bringing rough seas and coastal erosion/flooding issues. Elevated tides will be a concern as well. Meanwhile heavy snow will be a potential hazard over parts of the south-central mainland, within a broader area of snow and coastal rain. The approach of upper troughing and development of a triple point wave along the southern coast should also focus heavy precipitation along the southern coast east of the Kenai Peninsula and into the Panhandle during the mid-late week time frame. The majority of the state should see above to well above normal temperatures next week. Exceptions will be with some pockets of below normal readings over the southern mainland and Panhandle, as well as over about the southwestern third of the mainland by next Friday as the axis of the mean trough aloft approaches/arrives. Rausch Hazards: - Heavy precipitation across portions of the Alaska Panhandle and mainland Alaska, Wed-Thu, Nov 15-Nov 16. - Heavy snow across portions of mainland Alaska, Wed-Thu, Nov 15-Nov 16. - High winds across portions of mainland Alaska, Sun-Mon, Nov 12-Nov 13. - High winds across portions of mainland Alaska and the Aleutians, Wed, Nov 15. 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