Prognostic Meteorological Discussion
Issued by NWS
Issued by NWS
244 FXUS02 KWBC 110659 PMDEPD Extended Forecast Discussion NWS Weather Prediction Center College Park MD 259 AM EDT Tue Aug 11 2026 Valid 12Z Fri Aug 14 2026 - 12Z Tue Aug 18 2026 ...South-Central to Southeast U.S. Hazardous Heat Threat... ...Southwest/Greatasin/Rockies Monsoonal Heavy Rain Threat... ...North-Central U.S. to Midwest/Mid-Atlantic Heavy Rain Threat... ...Guidance/Predictability Assessment... Model and ensemble forecast spread is trending favorably lower over medium-range time scales. Despite lingering system timing and focus differences, overall forecast confidence has broadly improved with respect to flow evolution and inherent threat messaging given the reasonably well defined and persistent summer pattern. A favored composite of compatible models and ensembles tends to mitigate system variances consistent with individual predictability to provide a solid forecast basis overall consistent with the National Blend of Models and acts to maintain good WPC product continuity. ...Pattern Overview and Weather/Hazards Highlights... A protracted heatwave will broadly linger from the South-central to Southeast U.S. under the influence of a persistent upper ridge. Temperatures will remain well above normal as portions of the Southern Plains reach the lower 100s, while widespread 90s extend eastward across the Southeast. High dew points/humidity will keep heat indices elevated, resulting in dangerous heat conditions. Widespread record overnight temperatures will provide little relief. Major HeatRisk conditions are expected across a broad portion of the region, with locally Extreme HeatRisk possible. Meanwhile, monsoonal moisture and flow embedded vorts will channel over the Southwest/Great Basin and Rockies between an eastern Pacific upper trough and the western periphery of the southern U.S. upper ridge this period. This will lead to the development of scattered to numerous thunderstorms, particularly over the south- central Rockies states where a WPC Day4/Friday Excessive Rainfall Outlook (ERO) Slight Risk area has been introduced. The Day 4/Friday and Day 5/Saturday EROs also show a broad surrounding Marginal Risk areas. Some storms will produce excessive rainfall over short periods while moving rather slowly. Repeated convection may lead to flash flooding in vulnerable terrain, including burn scars, slot canyons, and urbanized areas. Elsewhere, progressive flow will persist across the U.S northern tier of the central to eastern U.S. overtop the potent southern U.S. upper ridge. Multiple shortwaves will cross the region through the period and interact with a slow-moving and wavy frontal zone extending from the northern/central Rockies into the Central Plains, Midwest, Ohio/Tennessee Valleys and into the East. Rich low-level moisture, instability, and forcing will support periodic clusters of showers and strong thunderstorms with locally heavy rainfall potential and flooding concerns. The Day 4/Friday ERO has introduced a Slight Risk threat area centered over the corn belt given repeat convection potential. The Day 4/Friday and Day 5/Saturday EROs also show broad surrounding Marginal Risk areas. 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 $$