028 FXUS01 KWBC 200809 PMDSPD Short Range Forecast Discussion NWS Weather Prediction Center College Park MD 400 AM EDT Thu Aug 20 2026 Valid 12Z Thu Aug 20 2026 - 12Z Sat Aug 22 2026 ...Heavy rain, flash flooding, and severe weather threats spreading from the Ohio/Tennessee Valley this morning to the Mid-Atlantic coast later today... ...Severe thunderstorms possible across the upper Midwest to the central Plains today, mainly over the north-central Plains on Friday... ...Dangerous heat persists in the South while building into the Southwest... As a cool air mass from Canada advances toward the northeastern U.S. against a persistent and stagnant heat dome anchored across the southern tier states over the next couple of days, the focus of heavy rain, flash flooding, and severe weather and thunderstorms will shift from the Ohio/Tennessee Valley this morning to the Mid-Atlantic coast later today. A convergence zone sandwiched between the stationary front to the south and the cold front from Canada will focus a corridor of enhanced rainfall. Heavy rain with embedded thunderstorms is expected along this corridor roughly from I-95 east to the northern Mid-Atlantic coast. WPC has highlighted this area for a slight risk of excessive rainfall mainly later today when daytime heating is maximized. In addition, SPC has highlighted a slight risk for severe weather where the main threat is damaging wind gusts. By tonight into early Friday, the heavy rain should temporarily exit the Mid-Atlantic coast as a low-pressure wave slides off the coast of southern New England. Some lighter rainfall may wrap around the low pressure wave toward southern New England on Friday. Day-time heating is forecast to trigger the next round of heavy thunderstorms later on Friday across the Carolinas to the Mid-Atlantic where a slight risk of excessive rainfall is highlighted. From Friday night into Saturday morning, showers and embedded thunderstorms are expected to advance up the Mid-Atlantic states as a trough of low pressure deepens over the Great Lakes. Over the midsection of the country, another round of severe weather is possible for eastern Nebraska into Minnesota and Wisconsin this afternoon into the evening ahead of a front trailing from a low pressure wave moving across Minnesota into the U.P. Michigan. SPC has outlined a slight risk of severe weather for the area where the main threat will be large hail, and isolated wind damage. On Friday, much of central and eastern Nebraska will yet again experience another round of severe weather as the trailing front pushes against the northern boundary of the heatwave across the South where ample moisture, strong instability and shear are in place to initiate some supercell thunderstorms. SPC has highlighted a slight risk for severe weather where the main threat will be isolated to scattered damaging hail (some greater than 2 inches) and some severe wind gusts for Friday afternoon into the evening hours. As for the Southeast, scattered to numerous thunderstorms are forecast within a very moist and unstable environment along a surface trough. Single to multi-cell convection will pose the risk for excessive rainfall where WPC has highlighted a slight risk for excessive rainfall from northern portions of South Carolina to the southern portions of Virginia. Meanwhile, monsoonal showers and thunderstorms will be most active during the late-day hours across the Four Corners states, where the WPC has highlighted a marginal risk of Excessive Rainfall through the next couple of days. In addition, a slight risk is in place across southern Arizona for today. Temperature-wise, the southern tier of the Lower 48 remains mired in a steamy air-mass even by mid-to-late August standards. Record highs and record warm minimum temperatures will be common with the Southeast at the heart of the anomalous heat through today. The upper ridge is forecast to strengthen over the Southwest while cool Canadian air dips further into the Great Lakes where showers will become more widespread heading into the weekend. Some cases of record-breaking warmth are expected in the Desert Southwest and Southern Plains as temperatures dip into the 40s near the Canadian border in the upper Midwest. Extreme Heat Warnings are in effect for much of the Desert Southwest, and Extreme Heat Warnings remain in effect across portions of the southern Plains to the Deep South. Heat Advisories are in effect for all of Florida and the southeast U.S. coast. Overnight lows will be so warm (low 80s in some cases) that, when combined with oppressive dew points, little-to-no relief from the scorching daytime highs will be available. Residents are advised to follow proper heat safety tips by limiting outdoor activity, staying hydrated, ensuring access to A/C or cooling centers, and checking on vulnerable friends, neighbors, and family members. Kong/Green Graphics available at https://www.wpc.ncep.noaa.gov/basicwx/basicwx_ndfd.php $$