Extended Forecast Discussion NWS Weather Prediction Center College Park MD 304 PM EDT Mon Oct 05 2020 Valid 12Z Thu Oct 08 2020 - 12Z Mon Oct 12 2020 ...Heavy rainfall from tropical cyclone Delta and the remains of Gamma headed for Gulf states and the Southeast... ...Strong winds, storm surge and coastal flooding likely to impact parts of the Gulf Coast as Delta approaches and then makes landfall... ...Major pattern change expected for the western U.S. with cooler temperatures and increasing precipitation... ...Overview... Much of the extended period will be in a progressive pattern with a trough over the East that slowly becomes replaced by ridging aloft, while a trough moves through the West and amplifies over the Plains. Models were generally better clustered for the eastern two-thirds of the country than with the system over the Pacific that moves through the West. A combination of the 06Z GFS/00Z ECWMF/UKMET was preferred for day 4 as it was the closest to the NHC track for Delta, day 5 replaced the UKMET with the CMC, and for the rest of the periods used a combo of the CMC/ECWMF/GFS and the 00Z NAEFS and EC ensembles. ...Weather/Hazard Highlights... Tropical Storm Delta is forecast to strengthen to at least a category 1 hurricane and accelerate between the subtropical ridge and T.S. Gamma before re-curving northward while either absorbing Gamma, or flinging its remains around its southern and southeast side. As of the latest NHC outlook (15Z issuance) it will move inland over south-central/southeast Louisiana on Friday and then continue to track north/northeast spreading heavy rainfall across the Gulf states/Tennessee Valley and into the Appalachians and Mid-Atlantic regions over the weekend/early next week. Strong winds, storm surge and coastal flooding will impact stretches of the Gulf Coast as Delta draws closer to the southern U.S. Localized intense rainfall may cause scattered/widespread urban and river flooding along its track. Across the West, a potent trough will favor a period of cooler than average temperatures along the West Coast and into the Great Basin by Sunday. Additionally, precipitation will increase through the end of the week and this weekend across the western states with snow possible in the highest terrain of the Cascades and the Northern/Central Rockies. This very much needed precipitation should provide some relief from ongoing fire weather concerns. Ahead of the upper trough and cold front, the area of possible record high temperatures shifts from the southern Rockies into the southern Plains with time. Campbell 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