Alaska Extended Forecast Discussion NWS Weather Prediction Center College Park MD 328 PM EDT Tue Oct 01 2019 Valid 12Z Sat Oct 05 2019 - 12Z Wed Oct 09 2019 Over the past day guidance has continued its recent trend toward improved agreement for the large scale flow. Nearly all solutions now show a fairly amplified but moderately progressive pattern featuring two significant features aloft. The first will be a mainland Alaska/Bering Sea trough (with closed low over the northwestern mainland) as of early day 4 Sat, expected to amplify into the Gulf of Alaska/northeastern Pacific with time. This evolution will lead to rapid weakening of initial low pressure near the northwest corner of the mainland in favor of Gulf low pressure. Then farther upstream an upper trough emerging from Asia will pick up Tropical Storm Mitag in the short range. The resulting system should eventually track over or just south of eastern Siberia around early next week and then approach the northwestern mainland by midweek, with a triple point wave in the process of forming over the northern Gulf at that time. The forecast pattern should favor heaviest precipitation over the extreme southeast mainland and Panhandle, with somewhat lower but still meaningful totals over parts of the southern and western mainland. Detail and timing differences are generally within typical error ranges for the time frame of interest with fairly even spread between opposite sides of the envelope--GFS/GEFS runs generally somewhat faster than the ECMWF/ECMWF mean with the CMC/CMC mean offering some support for either depending on the area. The 00Z CMC likely strays too far north with extratropical Mitag near the end of the period though. One notable area of spread involves the weekend/early next week Gulf low, and again individual ensemble spread seems to favor an intermediate solution. Members vary considerably in latitude and reflect aforementioned timing differences (with 00Z CMC members spread among both the GEFS and ECMWF members). Based on the favorable guidance comparisons in principle, today's forecast started with an operational model blend (06Z-12Z GFS and 00Z ECMWF/UKMET/CMC) and was able to keep an operational model emphasis into early day 7 Tue--with only 30 percent total 06Z GEFS/00Z ECMWF mean weight at that time. For the rest of the period the blend went closer to an even weight of models/ensemble means. This approach yielded better than average continuity with primary differences being better defined systems per latest agreeable models and somewhat faster frontal progression south of extratropical Mitag. 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 - Heavy precipitation across portions of the Alaska Panhandle and southeastern mainland Alaska, Sat-Sun, Oct 5-Oct 6. 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