Extended Forecast Discussion NWS Weather Prediction Center College Park MD 403 PM EDT Thu Oct 01 2020 Valid 12Z Sun Oct 04 2020 - 12Z Thu Oct 08 2020 ...Hot and dry conditions across The West expand into the central U.S. next week... ...Heavy rainfall threat for the Florida Peninsula through next midweek... ...Overview and Guidance/Predictability Assessment... Guidance overall favors reinforcement of a central to eastern U.S. upper trough position Sunday/Monday as energy digs to the lee of an amplified western North American upper ridge, then out through the Northeast/western Atlantic Tuesday. Models and ensembles differ with the extent of amplification/stream separation within the mean upper trough. The GFS and GEFS continue to be quicker in flattening the ridge into next week and more progressive/less amplified with the downstream upper trough than the ECMWF ensemble mean and especially the ECMWF. However, both of these global models have been trending toward a middle ground, with the GFS/GEFS indicating more coastal cyclogenesis while the ECMWF/EC mean speeds up the developing cyclone off the northeastern U.S. into the Atlantic. A solution on the more amplified side closest to the ECMWF ensemble mean is still preferred. After the departure of this system, models are in excellent agreement on a second upper trough dipping into the Great Lakes by the middle of next week, as the upper-level heights gradually lower across the Northwest. The morning WPC grid package was derived using a blend of the 00Z ECMWF/EC mean with the 06Z GFS/GEFS mean. More weights were given to the ECMWF/EC mean solutions on Day 4 to handle the East Coast cyclogenesis. The blend then progressively trends toward the ensemble means from days 5 to 7. ...Weather/Hazard Highlights... Upper trough instability and wavy frontal translation/focus will provide unsettled conditions and moderate rain potential from the Midwest/Great Lakes through the Ohio Valley and Northeast. A stalled front across the Florida Peninsula together with an influx of moisture from a couple of tropical systems passing to the south and southwest will focus a major threat of multi-day heavy rainfall and runoff issues through this period. The first tropical system is forecast to reach the Yucatan Peninsula this weekend into early next week before the second system moves into the western Caribbean region by Days 6 and 7. The upper ridge persisting across the West continues to offer hot and dry conditions with associated fire risks. Expect temperatures 5-15 degrees F above normal from the Desert Southwest up through the Northwest to expand eastward to the central/southern Plains next week. A few record high temperatures are possible. A cooling trend should then begin to set in across the Pacific Northwest by next Thursday. In contrast, a reinforcing cold air surge this weekend will keep temperatures of 5-15 degrees F below normal for much of the central to eastern U.S. Sunday before moderating as it shifts southeast behind a cold front early next week. Kong/Schichtel 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 Hazards: - Heavy rain across portions of the Southeast and the Mid-Atlantic, Sun, Oct 4. - Heavy rain across portions of the Southeast, Wed, Oct 7. - Flooding possible across portions of the Southeast and the Mid-Atlantic. - High winds across portions of the Great Lakes, the Upper/Middle Mississippi Valley, the Central Appalachians, and the Ohio Valley,Mon-Wed, Oct 5-Oct 7. - Much above normal temperatures across portions of California, the Northern/Central Great Basin, and the Pacific Northwest, Sun, Oct 4. 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