941 FXUS02 KWBC 271859 PMDEPD Extended Forecast Discussion NWS Weather Prediction Center College Park MD 259 PM EDT Thu Aug 27 2026 Valid 12Z Sun Aug 30 2026 - 12Z Thu Sep 03 2026 ...Hazardous Heat to broadly expand across the South-Central U.S. then Midwest to South next week... ...Overview... Dangerous late-summer heat will broadly spread across the central/southern Plains then Midwest/South this weekend into next week. Surges of monsoonal moisture will meanwhile continue to support daily showers and thunderstorms from portions of the Southwest to the Intermountain West/Rockies with localized flash flooding possible. Meanwhile, low pressure systems traversing southern and western Canada will push a wavy front across the northern tier of the CONUS and later dip into the east-central U.S. where rounds of showers and possibly strong to severe thunderstorms with locally heavy downpours are possible. Slowly dissipating leading frontal boundaries across the southern Mid- Atlantic and Southeast will also offer lingering risks for storms with heavy rain and local runoff issues. ...Guidance/Predictability Assessment... Models are in reasonably good agreement on the overall synoptic pattern evolution during the medium range period. The Ai models cluster well with the Euro and Canadian early in the period and are therefore favored in the blend through day 4. The ensemble means are introduced to the blend on day 5 and increased in weighting through the end of the period. The AiGFS and ECIAFS begin to diverge significantly on day 5 regarding the timing evolution of the mid-level low propagating through southern Canada/Upper Great Lakes, thus the ensemble means are used to mitigate this spread. ...Weather/Hazards Highlights... Under the influence of a main upper high/ridge, daily maximum temperatures across the Southern Plains will continue to rise into the 90s and 100s with oppressive heat indices. Record-breaking warm overnight temperatures across the southern tier will further limit recovery from the heat, resulting in widespread Major to Extreme HeatRisk that may cause heat related illnesses. As the upper ridge/high shifts eastward this weekend/next week, hazardous heat over the Southern Plains will steadily expand northeastward over the south-central U.S and lower/mid Mississippi Valley/Mid- South. Heat threat will overspread the Ohio Valley/South/Southeast mid- later next week. In this upper pattern transition, the excessive heat threat moderates over the Desert Southwest. Please see WPC's Key Messages for more extreme heat details. Monsoonal moisture streaming northward on the western to northern periphery of the upper ridge and ahead of locally showery Northwest U.S. upper troughing will continue to fuel scattered, diurnally driven convection from the Southwest and Intermountain West to the Rockies. Individual cells may lead to isolated instances of flash flooding for sensitive locations such as burn scars, favored terrain like slot canyons, and urban areas. Marginal Risk areas cover portions of these areas on the WPC Day 4/Sunday and Day 5/Monday Excessive Rainfall Outlooks (EROs). Multiple shortwaves rounding the top of the ridge and pivoting into the downstream and slowly deamplifying mean upper trough, will interact with wavy frontal systems will bring much of expected heavy rain and thunderstorms increasingly off the East Coast this weekend. Marginal Risk ERO areas spotlight an upstream focus over the upper Midwest/Great Lakes Sunday into Monday ahead of the triple-point associated with the eastward moving low pressure system across southern Canada. Marginal Risk ERO areas also highlight a lingering threat for locally heavy rainfall over the coastal Southeast/eastern Gulf Coast/Florida Sunday and Monday as wavy front gradually dissipates into early next week. Kebede/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 $$