Extended Forecast Discussion NWS Weather Prediction Center College Park MD 1130 AM EDT Sun Sep 29 2019 Valid 12Z Wed Oct 02 2019 - 12Z Sun Oct 06 2019 ...Heavy rain expected from portions of the Southern Plains to the Mid-Mississippi Valley... ...Anomalous warmth culminates over the eastern and southeastern U.S. Wed-Thu, while very chilly conditions moderate in the northern and northwestern states... ...Overview and Guidance/Uncertainty Assessment... Relatively zonal/progressive flow is expected to be in place across the CONUS during much of the medium range south of a more amplified flow regime in place from Alaska across Canada. The period of more zonal flow will begin by late Wed into Thu as an upper trough initially across the Rockies lifts out into the central U.S. with a wavy surface front progressing through most of the central and eastern U.S. by late week. Meanwhile, another upper trough is forecast to move through the Pacific Northwest and the northern Rockies late this week, prompting developing of a low pressure system across the Central/Northern Plains by this weekend the trough moves east. The WPC medium range forecast was based heavily on the 00Z ECMWF along with gradually increasing weight on ensemble means (ECENS/NAEFS) through time. The ECMWF was reasonably well-centered within the model/ensemble spread through most of the forecast period, lending to an overall preference toward that solution. The GFS showed differences even early on with the timing of the shortwave crossing the Northern Plains/Great Lakes Wed-Thu, and with the amplitude of the feature as it crosses the Northeast later in the week. Thus the GFS was not a preferred solution for this forecast update. ...Weather Highlights/Threats... Confidence is increasing that a band of heavy rain to impact portions of the Southern/Central Plains starting as early as Tue and persisting into the early portion of the medium range (Wed-Wed night) as moisture drawn northward from Tropical Storm Narda interacts with a frontal boundary. The potential for several inches of rainfall could result in the potential for flash flooding for some areas. Localized heavy rain is possible across portions of New England on Thursday ahead of a developing low pressure wave along the front. Meanwhile, deep-layer easterly flow will bring an influx of tropical moisture across southern Florida and into the Gulf of Mexico later this week. Very chilly conditions over the western U.S. into Northern Plains are expected to moderate through this week. Farther east, many locations from the Gulf Coast to the Mid-Atlantic will see daily record high temperatures Wed-Thu. As the strong upper ridge begins to weaken into the weekend, the heat will begin to gradually abate. Ryan 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