Extended Forecast Discussion NWS Weather Prediction Center College Park MD 210 PM EST Thu Nov 05 2020 Valid 12Z Sun Nov 08 2020 - 12Z Thu Nov 12 2020 ...Widespread mountain snows and colder weather for the interior western U.S. into the northern High Plains this weekend into Monday... ...Heavy rain likely across southern Florida with high winds possible for the Keys and the southern coast early next week as tropical cyclone Eta is forecast to track just to the south... ...Overall Synopsis... A deep upper level trough initially over the Intermountain West on Sunday will bring widespread mountain snows across the interior western U.S. into the northern High Plains. The cold air mass associated with the deep trough will make steady progress eastward across the country through the middle of next week, pushing the anomalous upper level ridge off the East Coast. Meanwhile, the future progress of tropical cyclone Eta will need to be watched for much of next week as models continue to indicate that it will likely meander in the vicinity of the eastern Gulf of Mexico. ...Guidance Evaluation/Preferences... The deterministic guidance this morning started out in excellent agreement on Sunday regarding the evolution of the western U.S. trough and the magnitude of the eastern U.S. ridge. From Monday onward, the deterministic solutions from the 00Z ECMWF and 06Z GFS were getting faster and faster away from their respective ensemble mean solutions regarding a low pressure wave tracking from the central U.S. toward the Great Lakes in the middle of next week along a cold front. The ensemble mean solutions are much more agreeable with WPC continuity. Therefore, the morning WPC prognostic charts were based on about 70% blend of the the 00Z EC mean and the 06Z GEFS from Day 5 onward. More of their deterministic solutions were used for Days 3 and 4. The ensemble means also served as a good starting point around Eta, with manual adjustments made according to the NHC track. ...Weather/Hazard Highlights... Heavy rainfall is becoming increasingly likely for portions of southern Florida as advancing moisture from the Caribbean interacts with persistent easterly post-frontal flow, as well as from the outer rain bands of Eta, which is currently forecast by the NHC to track close to the Florida Keys from later on Monday into Tuesday. The potential exists for several inches of rainfall along with some flooding. The building western U.S. trough will allow much colder temperatures to spread into the interior western U.S. this weekend, followed by much of the northern Rockies and into the northern Plains on Monday. Widespread high temperatures of 10 to 20 degrees below normal are expected, which will easily be a 30+ degree drop for some areas compared to late this week. A significant winter storm is likely across portions of the Northern Rockies, with moderate to heavy snow and potentially even blizzard conditions across parts of Montana. The opposite will hold true across the eastern U.S. through early next week, with temperatures that are expected to be 10 to 20 degrees above normal from the Midwest and Great Lakes region, and extending to the East Coast. Some daily record high temperatures will be challenged especially over the Ohio Valley. As the trough axis slowly advances eastward across the High Plains by early next week, moisture interacting with the front will likely bring locally heavy rainfall to some locations across the central Plains to the Midwest, with a swath of wintry precipitation expected for the northern portion of the area. Kong 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 Hazards: - Heavy precipitation across portions of the Central Plains, the Middle Mississippi Valley, the Great Lakes, the Upper Mississippi Valley, and the Northern Plains, Tue-Wed, Nov 10-Nov 11. - Heavy rain across portions of the Central Plains, the Middle Mississippi Valley, the Great Lakes, the Ohio Valley, and the Upper Mississippi Valley, Tue-Wed, Nov 10-Nov 11. - Heavy rain across portions of the Southeast, Sun-Tue, Nov 8-Nov 10. - Heavy rain across portions of the Central Appalachians, the Tennessee Valley, the Mid-Atlantic, the Southern Appalachians, the Southeast, and the Ohio Valley, Wed-Thu, Nov 11-Nov 12. - Heavy snow across portions of the Central Rockies and the Central Great Basin, Sun-Mon, Nov 8-Nov 9. - Heavy snow across portions of the Northern Plains and the Northern Rockies, Sun, Nov 8. - High winds across portions of the Central Plains, the Northern Plains, and the Northern Rockies, Sun, Nov 8. - High winds across portions of the Southeast, Sun-Mon, Nov 8-Nov 9. - Much below normal temperatures across portions of the Central Plains, the Central Great Basin, the Northern Plains, the Northern Rockies, the Central Rockies, California, the Northern Great Basin, the Pacific Northwest, and the Southwest, Mon-Thu, Nov 9-Nov 12. 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