Extended Forecast Discussion NWS Weather Prediction Center College Park MD 215 PM EDT Wed Oct 28 2020 Valid 12Z Sat Oct 31 2020 - 12Z Wed Nov 04 2020 ...Overview... The main upper-level feature present in the medium range period is a progressive trough moving through portions of the central CONUS over the weekend toward the East Mon/Tue, pushing a cold front across those regions. Meanwhile, ridging generally sets up over the West (other than a weakness in the subtropical flow slowly tracking east into southern California) through early next week before lowering heights may arrive there Tue/Wed. ...Guidance Evaluation/Preferences... Generally good agreement was seen with the 00Z/06Z model guidance, particularly with the initial trough and its associated low pressure system moving across south-central to eastern Canada, so a multi-model blend of deterministic models was able to be used through Mon. Predictability lessens somewhat by Tue/Wed especially across the West. Some zonal flow to potentially low amplitude troughing should flatten the ridge and push any remaining ridging into the central U.S., but details in the position/timing and strength of shortwaves vary from model to model and run to run, with no real consensus yet. So using a blend containing the 00Z EC and 06Z GEFS ensemble means for the later days of the forecast seemed prudent for now. ...Weather/Hazard Highlights... The respectable surface low forecast to track through south-central to eastern Canada will sweep a cold front across the Plains to the Eastern Seaboard over the weekend, bringing cooler than average temperatures. Temperatures of 5-15 degrees below normal are likely through Tue, and highs could be 20+ degrees below normal Mon in the Central Appalachians in particular. Light precipitation in the form of rain and possibly high elevation and lake effect snow is possible in the Great Lakes region/Northeast through early next week. The Mid-Atlantic may see light rain as well, while a couple of fronts near southern Florida could help cause light rain there. Underneath the ridging in the West, above normal temperatures are forecast, spreading into the Rockies Mon and the Northern/Central Plains and Upper Mississippi Valley closer to midweek. Modest precipitation is possible in the Pacific Northwest Tue/Wed as a front is expected to pass through, depending on how the upper-level pattern ends up evolving, but precipitation amounts do not appear to be unusually high for this time of year. Meanwhile, the central CONUS should have dry weather in the medium range. Tate 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