511 FXUS02 KWBC 100640 PMDEPD Extended Forecast Discussion NWS Weather Prediction Center College Park MD 240 AM EDT Mon Aug 10 2026 Valid 12Z Thu Aug 13 2026 - 12Z Mon Aug 17 2026 ...Multi-day heavy rainfall threat extending from parts of the Midwest to the Ohio Valley this week into the weekend... ...Hazardous heat forecast across much of the South-Central and Southeast U.S. through next weekend... ...Overview... A progressive regime across northern and eastern U.S. and the ridging over south-central U.S. will continue to bring a active pattern through the weekend into next week. The ridge will maintain hot conditions that can potential become hazardous across the southern Plains and Southeast. Multiple shortwaves will eject within the amplified northern flow, which will support thunderstorms and showers across the northern tier. Several days of repeated rainfall will bring 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 latest deterministic and ensemble guidance continues to show good agreement on the overall synoptic pattern, including the persistence of the southern U.S. ridge and an active northern stream regime. Confidence is comparatively higher through Thursday and Friday, while uncertainty increases into the weekend as individual shortwaves become increasingly difficult to resolve. This will lead to challenges with forecasting the amplitude and timing of small-scale features that may impact frontal boundaries and sensible weather. The ensemble guidance seems to alleviate some of these challenges. Therefore, a multi-model approach through the earlier portion of the period were incorporated in the forecast, while phasing in the ensemble means by the weekend. ...Weather/Hazards Highlights... A progressive northern-stream flow persist across the northern tier and eastern U.S. Multiple shortwave disturbances will traverse the northern tier through the weekend, and will interact with a slow- moving frontal zone extending from the northern/central Rockies into the central Plains, Midwest, Ohio Valley, and eventually across the Great Lakes and Northeast. The combination of rich low- level moisture, instability and repeated forcing along the boundary will support periodic clusters of showers and thunderstorms, with locally heavy rainfall and flooding concerns. With the potential for locally intense rainfall rates and slow moving storms redeveloping over the same area, a broad Marginal Risk has been highlighted in Day 4 (Thursday) Excessive Rainfall Outlook (ERO) across portions of the central Plains into Mid- Mississippi Valley, and Ohio/Tennessee Valley, while a Slight Risk highlights portions of the Ohio Valley, Midwest, and central High Plains. The frontal boundary will remain slow moving into the weekend reinforcing multiple days of showers and thunderstorms across the same areas, but by Sunday the frontal boundary will lift into the Great Lakes and Mid- Atlantic and portions of the Northeast, pushing the showers and thunderstorms further northeast into the Upper Midwest, Northeast, and Mid- Atlantic. Across the Southwest, Great Basin, Rockies, and interior California, a upper level trough will move into the West by late week, supporting low-level flow of monsoonal moisture, which will lead to the development of scattered to numerous thunderstorms. Some storms will produce heavy rainfall over short periods, despite relatively modest storm motions. Repeated convection may lead to flash flooding in vulnerable terrain, including burn scars, slot canyon, and urbanized areas. Therefore, a broad Marginal Risk on Day 4 ERO highlights much of the area with a Slight Risk over portions of the Rockies/Plains and portions of the Four Corners. Across the Southeast, a portion of the frontal boundary will drop southward into portions of the Southeast and a surface trough will develop ahead of the front by Friday and interact with warm moist airmass, which will support scattered thunderstorm development through the weekend. The southern Plains, Gulf Coast and Southeast will remain under the influence of the persistent upper ridge. Temperatures will remain well above normal, with portions of the southern Plains reaching the lower 100s and widespread 90s extending eastward across the Southeast. High dewpoints will keep heat indices elevated, resulting in potentially dangerous heat conditions where the heat persist for several consecutive days. Major HeatRisk conditions are expected across a broad portion of the region, with locally Extreme HeatRisk possible. Oudit 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 $$