Extended Forecast Discussion NWS Weather Prediction Center College Park MD 155 AM EST Wed Nov 4 2020 Valid 12Z Sat Nov 7 2020 - 12Z Wed Nov 11 2020 ***Major pattern change for the Western U.S. with snow and colder weather, and heavy rainfall for portions of Florida*** ...Overall Synopsis... A major pattern change will be taking place for the western U.S. for the upcoming weekend after an extended period of dry weather and above normal temperatures. A rather pronounced upper level trough will build in across the Intermountain West by Saturday along with a powerful cold front, and the opposite will hold true for the eastern half of the nation as a strong upper level ridge axis builds near the East Coast, in response to the amplifying western U.S. trough. The mid-upper level high will likely be strong enough to result in a slower than usual progression of the trough axis, with a potential blocking pattern setting up. ...Guidance Evaluation/Preferences... The deterministic and ensemble guidance remains in above average agreement through much of the forecast period on the synoptic scale across the continental U.S., largely owing to the amplified pattern that will be in place. By early next week, the CMC is stronger with the next Pacific Northwest system compared to the other guidance, but these differences are not that major for a day 5/6 forecast. There is improved model agreement regarding the future track of tropical cyclone Eta, with an eventual track into the southern Gulf of Mexico becoming more likely. The exact track will be dependent to some degree on the level of land interaction across Central America, and also how the broad monsoon gyre evolves. ...Weather/Hazard Highlights... The building western U.S. trough will herald the arrival of much colder temperatures from the Rockies to the West Coast by this weekend, with readings falling at least 25 degrees for many areas compared to highs late this week. There is a good chance for a significant precipitation event across portions of the Northern Rockies, where the latest winter weather probabilities for exceeding 4 inches of snow exceeds 70 percent this weekend across portions of Idaho and Montana. Maximum temperatures will likely be 10-20 degrees below normal across much of the Intermountain West and the Rockies by Sunday, and lasting into the middle of next week. A warming trend is forecast to commence across the central and eastern U.S. ahead of this system, with temperatures that will likely be 5-20F above normal as mid-level high pressure builds across the eastern states. As the trough axis slowly advances eastward over the western High Plains by early next week, moisture interacting with the front could bring locally heavy rainfall to some locations across the central Plains and Midwest. Elsewhere, heavy rainfall is becoming increasingly likely across the southern half of Florida as moisture interacts with persistent easterly post-frontal flow, and also moisture from the outer rain bands of Eta. 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