Extended Forecast Discussion NWS Weather Prediction Center College Park MD 107 PM EST Wed Nov 10 2021 Valid 12Z Sat Nov 13 2021 - 12Z Wed Nov 17 2021 ...Moderate to heavy precipitation into the Pacific Northwest Sunday-Monday... ...Lake Effect/enhanced precipitation this weekend through early next week across the Great Lakes... ...Guidance/Predictability Assessment... The latest guidance is in general agreement with the progression of an initial amplified trough in the East this weekend and a reinforcing shortwave behind that into the Midwest/East Sunday-Monday. By Tuesday/day 6, the 06z GFS becomes fast with the shortwave as it exits the Northeast, while the better clustering of the ensemble means/ECMWF/CMC supports something a little slower. The next system into the East Pac/Western U.S. comes by early next week, with the 06z GFS lagging significantly behind the ECMWF/CMC (and ensemble means) and noticeably flatter with the wave as it crosses the West next Tues/Wed. The WPC medium range suite used a general blend of the deterministic models (slightly more weighting towards the ECMWF/CMC over the GFS/UKMET) days 3-4. After this, the GFS (and UKMET which phased out after day 5) was replaced with the ensemble means to help mitigate the differences which begin to arise mid-late period. Maintained more emphasis on the ECMWF through the entire period though which was the deterministic solution closest to that of the ensemble means, both in the East and the West. ...Pattern Overview and Weather/Hazards Highlights... An amplified trough will pass slowly through the eastern CONUS, periodically reinforced by shortwaves rounding its southwest side. Its associated cold fronts sweep across the East this weekend with mainly light and scattered showers. South to southwest flow on the backside of the mean trough should help support enhanced lake effect precipitation/snows from the Upper Midwest/Great Lakes and into the northern Appalachians/Northeast. Temperatures should be generally around 10F below average for portions of the East Saturday through Tuesday. Moderation in the East is expected on Wednesday as low pressure moves across central Canada, with its cold front moving into the Upper Midwest, and the surface ridge axis slides towards the Southeast coast. For the Pacific Northwest, a cold front with a long fetch of Pacific moisture directed onshore, will drop slowly south along the Pacific northwest Coast Sunday-Monday resulting in moderate to heavy rainfall in the valleys and snow in the highest peaks. Overall, favorable flow should focus heavy rains and elevation snows mainly over the Olympics and Cascades, though some spill over precipitation is possible across parts of the northern Rockies next Tuesday into Wednesday. Until the Western trough moves into the area next Tuesday and Wednesday, temperatures are expected to be 10-15F above average before nudging slightly below average in the Northern Continental Divide on Wednesday. Santorelli/Roth 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 500mb heights, surface systems, weather grids, quantitative precipitation, winter weather outlook probabilities and heat indices are at: https://www.wpc.ncep.noaa.gov/medr/5dayfcst500_wbg.gif https://www.wpc.ncep.noaa.gov/medr/5dayfcst_wbg_conus.gif https://www.wpc.ncep.noaa.gov/5km_grids/5km_gridsbody.html https://www.wpc.ncep.noaa.gov/qpf/day4-7.shtml https://www.wpc.ncep.noaa.gov/wwd/pwpf_d47/pwpf_medr.php?day=4 https://www.wpc.ncep.noaa.gov/heat_index.shtml