Extended Forecast Discussion NWS Weather Prediction Center College Park MD 156 AM EST Thu Nov 05 2020 Valid 12Z Sun Nov 08 2020 - 12Z Thu Nov 12 2020 ***Major pattern change for the Western U.S. with snow and colder weather, and heavy rainfall for portions of Florida from Eta*** ...Overall Synopsis... A deep upper level trough initially over the Intermountain West on Sunday will herald a pattern change for much of the nation for the beginning of next week, with multiple shortwave perturbations rotating through it. Meanwhile, an anomalous upper level ridge will be centered just off the East Coast, and this will gradually be shunted eastward as the upper trough slowly progresses eastward over the Plains. Tropical Cyclone Eta is forecast to lift north from the western Caribbean this weekend as well, with increasing deep moisture and heavy rain likely affecting portions of southern Florida into the middle of next week. ...Guidance Evaluation/Preferences... The deterministic guidance is in excellent agreement on the synoptic scale features through Monday regarding the evolution of the western U.S. trough and the magnitude of the eastern U.S. ridge. Some timing differences emerge by Tuesday and into Wednesday as the surface low tracks from the central Plains to the Great Lakes region, with the GFS faster than the UKMET and ECMWF, and the CMC weaker. Noteworthy differences remain in the eventual track of Eta as it enters the southern Gulf of Mexico, with the ECMWF/EC mean farther west than the CMC and GFS that are closer to the Florida Coast. The overall WPC fronts/pressures forecast was primarily derived from a deterministic model blend through early Tuesday, and then transitioning to more of the ensemble means later in the forecast period. ...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 by Monday morning. 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 eastward from the West Coast this weekend, and then crossing the northern Rockies through Sunday and into 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 becoming more 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. It would not be surprising if some daily record high temperatures are set. 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 and Midwest. Hamrick 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: 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