Alaska Extended Forecast Discussion NWS Weather Prediction Center College Park MD 629 PM EST Sat Nov 16 2019 Valid 12Z Wed Nov 20 2019 - 12Z Sun Nov 24 2019 Models and ensemble means agree on fairly deep mean troughing aloft aligned near or just west of the western coast of the mainland for most of the period. This pattern will promote a stormy period with high winds/waves along with heavy precipitation. In particular a multi-day heavy precipitation event is likely over favored terrain along the southern coast and Panhandle. A leading system should reach the mainland by the start of the period early Wed with a front trailing into the northeastern Pacific. Guidance shows a fair degree of scatter for surface low track relative to the time frame, favoring a compromise approach. There is some suggestion of a frontal wave reaching the Gulf around Wed-Wed night but the 12Z GFS is a notable extreme with a deep/western wave due to dynamics aloft hanging back farther west than consensus. The 18Z GFS appears to correct this issue. Guidance expects the next storm to become quite deep as it tracks from the near the Aleutians to the southwestern mainland during the latter half of the week. An intermediate solution again looks most reasonable given existing spread for surface low track and timing. The 12Z GFS has one of the most southern tracks and is in the southern part of the full ensemble envelope (18Z GFS adjusted a little farther north) while the 12Z ECMWF is slower than the past couple runs and most other models/means. Based on data available through the 12Z cycle, the 06Z GFS run compared best to consensus for GFS input. Aside from aforementioned detail issues, guidance exhibits good enough consensus in principle to allow the initial blend to include exclusively operational models--12Z/00Z ECMWF, 06Z GFS, and 00Z CMC in order of higher to lower weight--from day 4 Wed into day 6 Fri. Overall agreement was still rather good into day 7 Sat leading to only modest 12Z GEFS/00Z ECMWF mean inclusion at that point. However by day 8 Sun the steady weakening of the mean trough aloft and rapidly increasing detail spread across the North Pacific favored rapid increase of ensemble guidance to 50-60 percent. In the days 7-8 period there is a signal for Pacific energy to produce an area of low pressure somewhere between the Alaska peninsula (12Z ECMWF) and Gulf of Alaska (12Z CMC), but with very poor clustering/continuity among the full range of guidance. Thus the manual forecast was on the conservative/progressive side in depicting this feature. 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 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