Extended Forecast Discussion NWS Weather Prediction Center College Park MD 324 PM 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... ...Increasingly wet pattern shaping up for parts of the eastern third of the U.S.... ...Overview... Remnants of tropical cyclone Beta will dissipate over the Southeast early in the extended period while strong troughing tracks from the Pacific Northwest, through the Rockies and into the Plains. Mid-to-upper level ridging will into the West this weekend, further strengthening the troughing to the east.With a deep trough moving in, the ridge over the Southeast will erode. ...Guidance/Predictability Assessment... Consensus showed Beta weakens/dissipating somewhere near northern Mississippi/Alabama and southern Tennessee by Friday. In general, the deterministic and ensemble means show troughing move into the eastern half/two-thirds of the CONUS during this period. However the specific details have not locked on just yet which is affecting the placement and quantity of precipitation, especially the Sunday onward. There is a signal for the Central/Northern Appalachians, Mid-Atlantic and Northeast to have a few inches of rain, possibly intense at times. Opted for a multi-model blend of the 00Z ECWMF/CMC/GFS/UKMET, 06Z GFS and the ensemble means for this forecast cycle... weighting of the ensemble increased during the mid and late periods. ...Weather/Hazard Highlights... Tropical cyclone Beta is expected to weaken/dissipate by the end of the week over the Gulf states while an upper-level trough tracks east to the north. While the central low of Beta tracks to the northeast and a cold front surges south, deep tropical moisture associated with Beta will spread across parts of the Lower Mississippi Valley, Tennessee Valley, Appalachians, and the Carolinas/southern Mid-Atlantic. Several inches of rainfall will be possible, especially near the terrain of the southern Appalachians where locally higher amounts may focus. Excessive rainfall and the risk for flash flash may become elevated for parts of northern Georgia and western South/North Carolina. The cold front mentioned above will bring modest rainfall to western Washington Thursday and Friday. Lingering showers are expected for this region into the weekend with the trailing shortwave trough. Once the front exits into the Plains, rainfall will develop along and ahead of the leading edge as it passes through the Northern Plains and Great Lakes region. Much warmer than seasonal average temperatures are expected for locations in the north-central U.S. Thursday and Friday prior to the arrival of a cold front; these warmer temperatures will spread to the Great Lakes region and the Northeast by the weekend. Cooler air will spill into the Plains behind the cold front, and with the increased cloud cover, will keep daily maximum temperatures below average for late September- for the Washington, Oregon, Idaho region initially and then shifting to the Great Lakes region by late weekend/early next week. Additionally, cloud cover and lingering precipitation from Beta will keep temperatures on the cooler side for parts of the Lower Mississippi Valley through Friday. Campbell 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