Extended Forecast Discussion NWS Weather Prediction Center College Park MD 1128 PM EST Wed Nov 10 2021 Valid 12Z Sun Nov 14 2021 - 12Z Thu Nov 18 2021 ...Moderate to heavy precipitation into the Pacific Northwest Sunday-Monday... ...Lake Effect/enhanced precipitation this weekend through mid next week across the Great Lakes... ...Guidance/Predictability Assessment... The latest guidance is in general agreement as the flow pattern goes from one that is amplified to more zonal. The WPC medium range suite used a general blend of the deterministic models, ensemble means, and the National Blend of Models to help mitigate the differences which begin to arise mid next week. ...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. Cold northwest 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 and Thursday as low pressure moves across central Canada, with its cold front moving into the Upper Midwest and Great Lakes, and the surface ridge axis slides off the East Coast. As this occurs, southwest flow keeps rain in the cards in and near the Great Lakes until the front clears the area next Thursday. 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 -- perhaps excessively in areas with burn scars -- 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 10-20F above average before nudging slightly below average in the Northern Continental Divide on Wednesday and Thursday. The warmer than average temperatures shift into the Plains ahead of the trough Monday through next Wednesday. Roth/Santorelli Hazards: - Heavy precipitation across portions of the Pacific Northwest and the Northern Great Basin, Sun-Mon, Nov 14-Nov 15. - Heavy rain across portions of the Pacific Northwest, Sun-Mon, Nov 14-Nov 15. 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