644 FXUS02 KWBC 091945 PMDEPD Extended Forecast Discussion NWS Weather Prediction Center College Park MD 345 PM EDT Sun Aug 9 2026 Valid 12Z Wed Aug 12 2026 - 12Z Sun Aug 16 2026 ...Multi-day heavy rainfall threat extending from parts of the Midwest to the Ohio Valley this week... ...Hazardous heat forecast across much of the South-Central and Southeast U.S. through next weekend... ...Overview... A progressive and unsettled regime across the northern and eastern U.S. and ridging over south-central U.S. will continue through at least early next weekend. The upper ridge will bring hazardous heat across the Southeast and southern Plains through Saturday. The shortwave embedded in the amplified flow will support thunderstorms and showers across the Northern Tier. Multiple days of slow-moving storms across portions of the Midwest and Ohio Valley may lead to flooding concerns. Troughing over the West Coast/Pacific Northwest will reinforce showers and thunderstorms activity stretching across the Southwest and Intermountain West/Great Basin. ...Guidance/Predictability Assessment... The large-scale pattern is reasonably well established through the first half of the period, with good agreement among the latest deterministic and ensemble guidance on the persistence of an active northern- tier flow and ridging over the south-central U.S. Confidence decreases with time concerning the amplitude and exact placement of shortwave troughs crossing the northern CONUS, which will impact the placement of frontal boundaries and areas of heavy rainfall. For the forecast, a preference towards a multi-model blend for the first portion of the period was used, while incorporating a heavier weight on the ensemble means by day 6. ...Weather/Hazards Highlights... Across the northern tier a series of shortwave energies will eject eastward into the broad troughing over eastern U.S. through the period. This will promote unsettled weather as the associated slow moving frontal boundary drapes across portions of the Rockies/Plains into the Great Lakes/Ohio Valley and across the Northeast. The warm and moist air mass ahead of these disturbances will support sufficient instability and lift for organized clusters, especially over the Midwest, Ohio Valley, and parts of the Mid- Atlantic. High rain rates from the slow moving and possibly repeating storms may lead to flash flooding concerns, which is highlighted in the Day 4 and 5 (Wednesday and Thursday) Excessive Rainfall Outlooks (ERO). The ERO shows a broad Marginal Risk across the northern/central Plains/Rockies into the Mid- Mississippi Valley, Ohio Valley/Tennessee Valley, and portions of the Southeast, with a Slight Risk over portions of the Ohio Valley/Central Appalachians (for Wednesday/Day 4) and Midwest to the Ohio Valley (for Thursday/Day 5). For the remainder of the week into the weekend, the surface low and associated stationary front will linger over the High Plains and central U.S. As sufficient moisture accumulates along the boundary and instability increases, daily thunderstorm chances will continue. With the potential for organized convection to develop as shortwaves energy, the flash flooding concerns may continue. Additional shower/thunderstorm chances will round the south-central U.S. ridge and bring rainfall chances to more of the Northern Plains and Southeast. Across the Southwest and throughout much of the Intermountain West and Rockies, an active convective pattern continues as the ridging weakens by midweek and monsoonal moisture continues to produce thunderstorms through the week. With chances for multiple days of repeated showers and thunderstorms, flash flooding concerns will increase across portions of the Southwest, Rockies, interior California, and Great Basin, especially over burn scars, urban areas, slot canyons, and steep terrain. The ridge over southwest will move eastward through the week and restrengthen over the Mid-South by next weekend, bringing hazardous heat across the Southeast, Gulf Coast, and portions of the Southern Plains. With high humidity from the Gulf, heat indices may become oppressive as widespread Major HeatRisk with locally Extreme HeatRisk levels spreads across much of the area. Portions of the southern Plains will see highs in the low 100s, while the Southeast will see mid to upper 90s. Heat- related impacts could become significant where the combination of high temperatures and humidity persist for several consecutive days. Oudit/Snell Additional 3-7 Day Hazard information can be found on the WPC medium range hazards outlook chart at: https://www.wpc.ncep.noaa.gov/threats/threats.php WPC medium range 500mb heights, surface systems, weather grids, quantitative precipitation forecast, excessive rainfall outlook, winter weather outlook probabilities, heat indices and Key Messages 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/#page=ero https://www.wpc.ncep.noaa.gov/wwd/pwpf_d47/pwpf_medr.php?day=4 https://www.wpc.ncep.noaa.gov/heat_index.shtml https://www.wpc.ncep.noaa.gov/#page=ovw $$