471 FXUS02 KWBC 140720 PMDEPD Extended Forecast Discussion NWS Weather Prediction Center College Park MD 320 AM EDT Fri Aug 14 2026 Valid 12Z Mon Aug 17 2026 - 12Z Fri Aug 21 2026 ...Long-duration heat wave continues in the Southeast... ...Heavy rain threat gets renewed in Midwest by Tuesday... ...Overview... Southern tier upper ridging will be well established into next week and bring continued 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 northern tier. Rainfall amounts are forecast to peak in the Midwest Tuesday and the Great Lakes Wednesday, with some flash flooding threat. Additionally, some monsoonal moisture coming north under the ridge will allow for convection in the Southwest and High Plains. ...Guidance/Predictability Assessment... Model guidance remains quite agreeable regarding the broad upper ridge stretching across the southern tier early next week. As the week progresses, troughing across the northeastern quadrant of the U.S. could sink south and limit the upper high to the southwestern U.S. Farther west, there have been considerable model differences with the potential for energy to come into the Northwest. Through its 18Z run, the GFS had been persistent in showing an aggressive shortwave digging through the Northwest by Tuesday-Wednesday forming a closed low, out of phase with basically any other guidance. Fortunately, the new 00Z GFS has backed off and now shows a shallower shortwave more like the other dynamical and AI models. There remain some model differences with the evolution of this and other shortwaves, but more within typical spread for the medium range period. Namely, the 00Z GFS is a little deeper and slower with the shortwave in the central Plains by Thursday, while the 00Z ECMWF is on the aggressive side with the strength of a surface low moving through the Great Lakes region Wednesday eastward. For late week, troughing looks to march east through the Pacific toward North America, potentially from both the midlatitudes and the Northeast Pacific. 00Z model guidance has converged somewhat on the timing of this troughing, though minor differences remain. The ridging just downstream across the West may extend northward in response. The WPC forecast was based on a multi-model blend not favoring the older GFS runs, though the 00Z GFS seems reasonable enough to include in a blend. As the period progressed, increased the proportion of ensemble means to about half by Day 7 amid the increasing spread. ...Weather/Hazards Highlights... The 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. 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 is in place in the Day 5/Tuesday Excessive Rainfall Outlook for this 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 warm 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 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 $$