Alaska Extended Forecast Discussion NWS Weather Prediction Center College Park MD 326 PM EDT Mon Oct 21 2019 Valid 12Z Fri Oct 25 2019 - 12Z Tue Oct 29 2019 The dominant focus of the forecast will be the expected amplification of the pattern as the deep extratropical evolution of Neoguri reaches and lingers near the Aleutians. The strengthening deep-layer gradient between the upper low/trough and downstream ridge that builds into the northeastern Pacific and mainland Alaska/northwest Canada will bring a significant amount of moisture into the Alaska Peninsula and a many portions of the mainland. The GEFS/ECMWF means reflect the overall guidance agreement for this evolution, with both showing precipitable water values reaching 3-4 standard deviations above normal in the late Sat-Sun time frame. Expect highest precipitation totals along southward/southeastward-facing terrain along the Alaska Peninsula and southern coast of the mainland. Somewhat less extreme but likely still very significant precipitation should extend into other portions of the southern and western mainland. Extratropical Neoguri will bring areas of strong winds and high waves as well. As for the guidance evaluation, solutions cluster fairly well for extratropical Neoguri late this week with the main adjustment from yesterday being a slightly southward trend by Sat--though not as far southward as the 00Z CMC (12Z run has returned northward). By the weekend into next week there are persistent uncertainties over details of one or more separate surface lows along the leading front and into the Bering Sea. Based on guidance available through arrival of the 12Z GFS, an operational model blend highlighting the 06-12Z GFS and 00Z ECMWF represents consensus details for extratropical Neoguri during the first half of the period. Transitioning the forecast toward an even weight between the models and 06Z GEFS/00Z ECMWF means later in the period accounts for the most common details in the guidance and also the agreeable larger scale pattern. Farther upstream the models and ensembles have so far been quite varied and inconsistent with the ultimate extratropical evolution and track of Typhoon Bualoi. Thus far a higher percentage of guidance indicates a southern track that would miss the Aleutians. Currently GFS/GEFS-based guidance is generally on the faster side of the spread, and given historical biases the preference is to lean the aforementioned blend partially toward the ECMWF/ECMWF mean by days 7-8 Mon-Tue. Guidance has not been very consistent with some aspects of higher latitude flow as well. Latest consensus brings a shortwave initially just west of the northern mainland eastward with time, becoming flatter as the upper ridge builds to the south. The 00Z CMC was questionably fast/amplified on Fri while the array of new 12Z guidance suggests the GFS could be a tad amplified with the shortwave by late Fri-early Sat. 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 Alaska Hazards... - Heavy precipitation across portions of mainland Alaska, Sat-Mon, Oct 26-Oct 28. - Heavy rain across portions of mainland Alaska and the Aleutians, Fri, Oct 25. - Heavy snow across portions of the Alaska Panhandle and southeastern mainland Alaska, Thu, Oct 24. - High winds across portions of the Aleutians, Thu-Fri, Oct 24-Oct 25. - High significant wave heights for coastal portions of the northeast Gulf of Alaska and the Alaska Panhandle, Thu, Oct 24. 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