Extended Forecast Discussion NWS Weather Prediction Center College Park MD 1202 PM EST Wed Nov 04 2020 Valid 12Z Sat Nov 07 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 from Eta... ...Overall Synopsis... A rather pronounced upper level trough will close into a low as it builds down the West Coast Thursday night through Friday night before lifting northeast across the Intermountain West to Montana and being reinforced through the weekend. Meanwhile, ridging, centered on the Mid-Atlantic, will build. The mid-upper level high will likely be strong enough to result in a slower than usual progression of the western trough axis, with a potential blocking pattern setting up. Eta will lift north from the western Caribbean this weekend as well, with advancing moisture and heavy rain likely affecting south Florida into the middle of next week. ...Guidance Evaluation/Preferences... Above normally good agreement on this amplified synoptic pattern (not for Eta, more on that below) among the 00Z ECMWF/UKMET and 06Z GFS allowed deterministic guidance to be exclusively used through Day 5 and the UKMET (only available to WPC through Day 5) replaced by the 06Z GEFS/00Z ECENS means through Day 7. 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. The 00Z CMC remains stronger with the reinforcing Pacific Northwest system Saturday night which leads to a stronger, slower, and more southerly track for the low across the Plains to the Upper Midwest during the first half of next week compared to the other guidance. The ECMWF remains more bullish with the track of Eta as it approaches the southeast Gulf from Cuba early next week. The NHC track is a little faster than the most recent deterministic and ensemble means. ...Weather/Hazard Highlights... Heavy rainfall is becoming increasingly likely for at least southern coastal 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 NHC to track to the Florida Keys by Monday morning. Please see NHC for further information on Eta. The building western U.S. trough will allow much colder temperatures to spread east from West Coast this weekend, crossing the northern Rockies on Sunday. Max temperatures of 15 to 20 degrees below normal is expected to set several low max records across CA and the western Great Basin Saturday through Monday. with readings falling at least 25 degrees for many areas compared to highs late this week. A significant precipitation event is expected across portions of the Northern Rockies, where the latest winter weather probabilities for exceeding a quarter inch of frozen precip is high for much of MT Saturday and Sunday. A strong warming trend under the building eastern ridge will occur across the central and eastern U.S. ahead of this system, with temperatures that 15 to 20F above normal spread from the northern Plains this weekend to the Northeast through early next week. Several record high temperatures are forecast for the Upper Midwest this weekend and Northeast early next week while scores of high minimum temperature records are forecast to by topped across the central and northern Plains then throughout the east through this time. As the trough axis slowly advances eastward over the western High Plains by early next week, moisture interacting with the front looks to bring locally heavy rainfall to some locations across the central Plains and Midwest. Jackson 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