Extended Forecast Discussion NWS Weather Prediction Center College Park MD 441 PM EDT Wed Oct 07 2020 Valid 12Z Sat Oct 10 2020 - 12Z Wed Oct 14 2020 ...Heavy rainfall from Hurricane Delta to slowly wane over the Ohio Valley Sat into Sun... ...Major pattern change expected for the western U.S. with cooler temperatures and increasing precipitation into early next week... ...Overview and Guidance Evaluation/Preferences... The medium range period (Saturday through next Wednesday) should exhibit a modestly amplified but still progressive pattern with a trough over the East that slowly weakens, while a trough moves through the West and amplifies over the Plains/Midwest/Great Lakes. Hurricane Delta is forecast to lift smartly out of the Lower Mississippi & Tennessee Valleys while weakening as a robust cold front moves across the Plains early next week. Models and ensembles (through the 00Z/06Z cycle) continued to exhibit a considerable amount of spread for a relatively short lead time, especially off/into the West Coast. There, preferred the cluster near the 00Z ECMWF/Canadian that continued the trough eastward rather than leave a southern end-tail upper low behind off Baja Mexico (GFS/UKMET). The GFS/GEFS were then quicker and less amplified than the ECMWF/Canadian and their ensembles with the burgeoning upper trough mid-continent. To the east, the 15Z NHC track with Delta was nearer to the GFS (quicker than much of the ensembles) but a very recent trend has shifted quicker as the system transitions from tropical to post-tropical and becomes absorbed into the flow. By next Tue/Wed, weighted the 00Z ECMWF ensembles and NAEFS mean heavily as the cold front slowly moves eastward. ...Weather/Hazard Highlights... Hurricane Delta is forecast to move out of the ArkLaMiss to the north/northeast while weakening, becoming entangled in a front as it does so. This will spread modest to locally heavy rainfall through the Tennessee Valley with generally lower amounts into the central Appalachians/Mid-Atlantic regions later this weekend. Across the West, a potent trough will favor a period of cooler than average temperatures along the West Coast and into the Great Basin/northern Rockies by Sunday. Precipitation will move through the West with snow likely in the higher terrain of the Cascades and the Northern/Central Rockies into Monday. This very much needed precipitation should provide some relief from ongoing fire weather concerns. Due to the relatively zonal flow/progressive pattern, areas east of the Rockies are expected to see near average temperatures due to downslope flow offsetting the cold advection, even in the wake of a cold front early next week. Record highs could be threatened across portions of NM/TX this weekend before the cold front/upper trough advance into the region. Mild temperatures for mid-October are also expected into the Great Lakes Mon/Tue and across the Northeast next Wednesday ahead of the lumbering cold front. Fracasso/Roth Hazards: - Heavy precipitation across portions of northern Idaho, Sun-Mon, Oct 11-Oct 12. - Heavy precipitation across portions of northwestern Wyoming, Sun, Oct 11. - Heavy rain across much of the mid-Mississippi Valley, the Tennessee and Ohio Valleys into the central and southern Appalachians and the interior Mid-Atlantic, as well as the Pacific Northwest from the Cascades westward, Sat-Sun, Oct 10-Oct 11. - Flooding possible across portions of the Lower Mississippi Valley to the Louisiana coast. - Flooding occurring or imminent across portions of the Southeast. - High winds across the interior portion of the lower Mississippi Valley, Sat, Oct 10. - Much above normal temperatures across much of the Great Plains into the nearby Rockies and into the Upper Midwest, Sat-Sun, Oct 10-Oct 11. - Much above normal temperatures across much of the northern High Plains and nearby Rockies, Sat, Oct 10. 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