010 FXUS02 KWBC 141853 PMDEPD Extended Forecast Discussion NWS Weather Prediction Center College Park MD 253 PM EDT Fri Aug 14 2026 Valid 12Z Mon Aug 17 2026 - 12Z Fri Aug 21 2026 ...Long-duration heat wave continues across the South/Southeast... ...Midwest Heavy Rain/Flooding Threat renews Tuesday/Wednesday... ...Overview... Ample southern tier U.S. upper ridging should be well established into next week and bring more hazardous heat to the south-central U.S. and Southeast. To the north of the ridge, relatively active flow will produce rounds of rain and thunderstorms across the U.S. northern tier. In this pattern, rainfall amounts are forecast to peak in the Midwest Tuesday and the Great Lakes Wednesday, along with local strong to severe convection and flash flooding threats. Additionally, some monsoonal moisture coming north under the ridge will allow for convection in the Southwest and High Plains. ...Guidance/Predictability Assessment... Medium-range guidance clustering continues to improve with the latest several run cycles to bolster forecast confidence. Lingering shortwave and local convective rainfall focus variances tend to be mitigated with a guidance composite forecast approach. Favor a transition from a composite model blend Tuesday-Thursday to a broader model/ensemble mean/machine learning blend later next week given some uncertainty growth. This plan acts to maintain good WPC product continuity and threat messaging that remains overall reasonably well in line with the National Blend of Models. ...Weather/Hazards Highlights... It generally remains the case that strong upper ridge remaining positioned over the southern U.S. will maintain hot conditions across the southern Plains through the Lower Mississippi Valley, Tennessee Valley, and Southeast. Afternoon temperatures will commonly reach the upper 90s to lower 100s across the interior South, while high humidity and persistent elevated dewpoints will produce oppressive heat indices of 105-115 degrees. Record-breaking warm overnight temperatures will further limit recovery, particularly where several consecutive days of heat occur. Widespread Major to Extreme HeatRisk conditions should persist into much of next week and also gradually spread over the Southwest U.S.. Several consecutive days of high heat stress can lead to heat- related illnesses. See WPC's Key Messages for more information. Shortwave energy moving through the northern tier will carry frontal systems that could focus moisture for rounds of showers and thunderstorms next week. After some rain in the northern Rockies/Plains to Upper Midwest Monday, stronger energy and a cold front are forecast to bring increasing rain amounts to the Upper Midwest in particular by Tuesday. A Slight Risk remains in place in the Day 5/Tuesday Excessive Rainfall Outlook for afternoon and overnight strong to severe thunderstorm and MCS activity. Enhanced rainfall could continue into the Great Lakes region Wednesday, with some rain chances starting to spread into the Northeast as well. Farther south, a weak cold front or two should provide a focus for scattered thunderstorms in the Mid- South to southern Mid-Atlantic on Monday and across the Southeast Tuesday- Wednesday in the hot and unstable airmass. By Thursday this activity may all combine into chances for scattered showers/storms across the Eastern Seaboard. Meanwhile, some monsoonal moisture could bring scattered diurnally driven convection to the Southwest. Monsoon coverage should likely be less than during the short range period, with less support aloft as the upper ridge builds. But some moisture advecting north while additional energy rounds the north side of the upper ridge could lead to more rounds of rain/storms in the north-central U.S. later next week. Tate/Schichtel 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 $$