Alaska Extended Forecast Discussion NWS Weather Prediction Center College Park MD 554 PM EST Sun Nov 17 2019 Valid 12Z Thu Nov 21 2019 - 12Z Mon Nov 25 2019 Models and ensemble means continue to show very good agreement on fairly deep mean troughing aloft becoming aligned near or just west of the western coast of the mainland for most of the period, slowly weakening by early next week. This kind of pattern will promote a stormy period featuring heavy precipitation along with high winds/waves for some. In particular, a multi-day heavy precipitation event appears likely over favored terrain along the southern coast and the Panhandle. The forecast period begins with lead shortwave energy crossing the Panhandle on Thursday while a rather deep cyclone (near 960mb) tracks across the Aleutians and into the eastern Bering Sea, eventually settling across the southwest mainland by the start of next weekend. Expect periods of high winds/waves for the Aleutians and western mainland coast. Less predictable pieces of energy should round the base of the mean upper trough into the Gulf of Alaska providing continued support for heavy precipitation along the southern coast and Panhandle through at least next weekend. Models show remarkable agreement on this system and so a majority blend of the latest 12z models (GFS/ECMWF/CMC) was used which maintains good WPC continuity. The biggest forecast differences arise not until the end of the period as another system lifts north and east towards the Gulf of Alaska. Models continue to struggle both with timing and intensity of this with the 12z GFS the fastest with this next wave, while the ECMWF is notably slower. The 12z CMC is also slower and far deeper so the CMC was taken out of the blend after day 6. The ensemble means would favor something slower and more in line with the ECMWF. Behind this, another cyclone drops down towards/across the far western Aleutians by day 8, and again, the deterministic models show significant differences with timing/progression of this. For both systems discussed, a blend of the agreeable ensemble means (12z GEFS and 00z ECENS) was used for days 7-8. The ECMWF also made up a small portion of the blend for days 7-8 to add a bit of definition to the usual washed out means given that it was the deterministic model that most closely resembled the mean pattern. Santorelli 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