Extended Forecast Discussion NWS Weather Prediction Center College Park MD 255 AM EDT Mon Sep 21 2020 Valid 12Z Thu Sep 24 2020 - 12Z Mon Sep 28 2020 ...Lingering heavy rainfall possible on Thursday with remnants of Beta... ...Overview... Strong troughing will push through the Northwest Thursday and into the Plains by Saturday as the remnants of Beta dissipate over the Southeast. Upper ridging is forecast to build into the West this weekend which will favor increased troughing over the East, squashing the ridge over Florida. ...Guidance/Predictability Assessment... Through the 12Z/18Z guidance suite, deterministic models were clustered enough Thu-Fri to use a consensus blend as T.D. Beta decays over the lower Mississippi Valley. Upper trough to the north will slide eastward out to sea on Saturday. To the west, guidance has come into much better agreement on the progressive but digging trough through the Rockies Friday and the Plains this weekend. With good ensemble agreement a consensus position sufficed. Upper ridging will build into the West/Southwest next Sun/Mon but the GFS/GEFS were less bullish than the ECMWF/Canadian/ECMWF ensembles. With a digging trough in the East and another deep trough in the Gulf of Alaska, preferred the ECMWF-led cluster but did temper this by a minority GFS/GEFS weighting given the lead time. Cold front could push all the way into the Gulf of Mexico in about a week should the pattern amplify as much as forecast. ...Weather/Hazard Highlights... Beta remnants are forecast to take a slow path northeastward across the South to the southern Appalachians Thursday into Friday, in tandem with an upper trough to the north. With some flow off the Gulf, pockets of locally heavy rain along and out ahead of its track are possible. Uncertainty with rainfall remains high with the details but a gradual winding down of the system is expected by the end of the week. A cold front out ahead of the western upper trough will bring modest rainfall to western Washington Thursday and Friday. Showers will continue behind the front with a trailing upper shortwave trough over the northern Rockies. Downstream, rainfall will develop and expand over the northern Great Plains into the Great Lakes this weekend. As the trough digs into the Midwest, Gulf moisture will flow northward and could help expand a larger area of modest rain along the Appalachians next week. Temperatures will be above to much above normal across the north-central U.S. ahead of the Pacific cold front. Warm conditions will spread through the Great Lakes this weekend and into the Northeast. By contrast, clouds and rain will keep max temperatures cooler than normal over the lower Mississippi Valley Thu-Fri as Beta weakens. Cooler max temperatures are expected for WA/OR/ID in the wake of the cold front later this week. This will eventually translate eastward to the Great Lakes Sunday into Monday. Fracasso 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