Extended Forecast Discussion NWS Weather Prediction Center College Park MD 1230 PM EDT Fri Oct 30 2020 Valid 12Z Mon Nov 02 2020 - 12Z Fri Nov 06 2020 ...Heavy Precipitation pattern for the Pacific Northwest Tuesday through Thursday... ...Overview... An anomalously strong and cold upper trough will lift north from New England Monday with upper troughing lingering over New England into Tuesday. Meanwhile a broad ridge over west-central Canada breaks down through Tuesday night allowing fast zonal flow to set up across the CONUS. An East Siberian trough rounding/phasing with a persistent low over southern Alaska develops over the Gulf of Alaska Wednesday, shifting south off the BC coast Thursday which maintains the broad zonal flow until it digs farther south off the West Coast Friday. Troughing well offshore the Pacific Northwest directs high moisture Pacific into western WA Monday night with heavy precipitation in the Olympics/Cascades Tuesday/Wednesday with lowering snow levels through this time before the focus shifts south into OR and the northern Rockies Wednesday night into Friday. Aside from wet weather in the Northwest, dry conditions prevail for the rest of the lower 48 starting Monday night (lake enhanced snow of Lake Ontario lingers over Upstate NY Monday night). Below normal temperatures over the East will moderate in the first half of the week as the above normal temperature across The West expands east. ...Guidance Evaluation/Preferences... The 00Z ECMWF/06Z GFS are in much above normal agreement through the middle of next week, making for a rather high confidence forecast. The 00Z UKMET is stronger/slower with the initial trough/low over New England while the 00Z CMC is weaker/faster with the wave coming into WA on Tuesday. Therefore a blend of the 00Z ECMWF/06Z GFS, increasingly to the 00Z ECENS mean/06Z GEFS mean by Day 5 was preferred. ...Weather/Hazard Highlights... Cold air continuing to spill southeast from the Northeast low on Monday should threaten several low maximum temperature records along the Eastern Seaboard Monday and in New England on Tuesday. Lake enhanced snow can be expected to linger into Tuesday downwind of Lake Ontario. Above normal temperatures over the West will also spread eastward next week into the Plains/Midwest/Great Lakes/Northeast. Record high temperatures are most likely in southern CA Tuesday through Friday. Heaviest precipitation is expected over the Pacific NW, particularly Washington State Tuesday and Wednesday following an atmospheric river. Rains and lowering elevation snows will spread over much of the Northwest Tuesday through Friday next week. Jackson Additional 3-7 Day Hazards information can be found on the WPC medium range hazards 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