Extended Forecast Discussion NWS Weather Prediction Center College Park MD 258 AM EDT Sun Oct 18 2020 Valid 12Z Wed Oct 21 2020 - 12Z Sun Oct 25 2020 ...Guidance Evaluation/Preferences... Guidance now offers a reasonably well clustered pattern evolution for much of the coming week. The pattern will be highlighted by a series of broad upper troughs over much of the lower 48, save lingering ridging over just offshore the Southeast. Forecast spread does grow heading into next weekend. This is especially evident with potential upper trough development over the West, but the newer 00 UTC GFS/ECMWF are now in better agreement than prior runs. Meanwhile towards the end of the week, moisture may be drawn northward from the Gulf of Mexico into the east-central Gulf states/Florida as a potential tropical low develops and lifts northward from the western Caribbean Sea as per latest NHC. The WPC medium range product suite was based from a blend of the GFS/GEFS mean, the ECMWF/ECMWF ensemble mean and the National Blend of Models. Blend weighting emphasis was applied to the models Wed-Fri, then the ensemble means heading into next weekend consistent with lingering uncertainty. ...Weather/Hazard Highlights... A series of wavy frontal systems with modest moisture will focus periods of moderate precipitation from the Northwest/Rockies and north-central U.S./Midwest to the Northeast. Post-frontal Canadian cold air surges will dig through the Northwest/Great Basin/central U.S. and eventually across the East. Temperature profiles favor periods of snow for the Cascades, the northern Rockies and the N-central states. The highest chance of heavy snows remains for the northern Rockies. Meanwhile, the heaviest rains may focus over the Upper Midwest and Great Lakes Wed/Thu with frontal wave genesis and passage. Farther south, moisture may increase into Florida and the east-central Gulf states late week as a tropical low is forecast to move slowly northward from the western Caribbean Sea. Schichtel 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