Extended Forecast Discussion NWS Weather Prediction Center College Park MD 230 PM EDT Sat Oct 17 2020 Valid 12Z Tue Oct 20 2020 - 12Z Sat Oct 24 2020 ...Guidance Evaluation/Preferences... Guidance continues to offer a well clustered larger scale forecast evolution through medium range time scales. This pattern will be highlighted by a broad upper trough over much of the lower 48, save lingering ridging over the Southeast. Despite the active northern stream across the northern tier states, there is relatively good agreement between the ECMWF/EC mean and the GFS/GEFS solutions on the timing of individual embedded shortwave energy. Towards the end of next week, moisture may be drawn northward from the Gulf of Mexico into the east-central Gulf states/Florida consistent with potential flow amplification over the nation as a potential tropical low develops over the western Caribbean Sea as per NHC. The WPC medium range product suite was based on an even blend of the 06 UTC GFS/GEFS together with the 00 UTC ECMWF/EC ensemble means. The CMC showed a rather different timing and evolution of the overall pattern and thus was excluded from the blend. This maintained good WPC continuity. ...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 into the Great Lakes. Temperature profiles favor periods of snow for the Cascades, the northern Rockies and the Dakotas. The highest chance of enhanced snows is forecast for the northern Rockies towards the end of next week. Meanwhile, the heaviest rains may focus over the upper Midwest to the Great Lakes Thu-Fri ahead of a warm front and an reinforcing surge of cold air from western Canada. Farther south, moisture may increase into Florida and the east-central Gulf states late next week as a tropical low is forecast to move into the western Caribbean Sea together with expected gradual amplification of the upper-level pattern over the U.S.. Kong/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