Extended Forecast Discussion NWS Weather Prediction Center College Park MD 251 AM EDT Sun Sep 20 2020 Valid 12Z Wed Sep 23 2020 - 12Z Sun Sep 27 2020 ...Rainfall threat from Beta for the lower Mississippi Valley... ...Overview... A deep trough over the Gulf of Alaska will move through the Pacific Northwest and western Canada later this week before moving into the Corn Belt/Upper Midwest next weekend. Tropical Storm Beta will likely be weakening over southeastern Texas into Louisiana with a diminishing heavy rainfall threat. Upper ridging will work its way back into the Southwest and also across Florida. ...Guidance/Predictability Assessment... Through the 12Z/18Z cycle, the deterministic models offered a reasonable clustered starting point with adjustments made for the track of Beta and Teddy to the northeast of Maine. By the end of the week, the GFS became most different from the otherwise good consensus of the ECMWF/Canadian and ECMWF ensembles (somewhat the GEFS ensembles too) with the quicker pace of troughing through the Rockies into the Plains. The ECMWF ensemble mean has been steadier with this evolution than the GEFS, and the strong jet across the eastern North Pacific suggests a quicker flow as well. ...Weather/Hazard Highlights... Tropical Storm Beta is forecast to take a slow path northeastward into southwest LA to the southern MS Valley and spread locally heavy rain along and out ahead of its track. Uncertainty remains high with the details but a gradual winding down of the system is expected late in the week. A cold front and trough from the Gulf of Alaska will bring several days of rainfall to western WA/OR Wednesday through Friday. Showers will continue behind the front over the northern Rockies. Temperatures will be above to much above normal across the north-central U.S. ahead of the Pacific cold front. Mild temperatures will spread through the Great Lakes next weekend and into the Northeast. By contrast, clouds and rain will keep temperatures cooler than normal over the lower Mississippi Valley Wed-Fri as Beta weakens. Cooler temperatures are expected for WA/OR in the wake of the cold front. 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