129 FXUS01 KWBC 190817 PMDSPD Short Range Forecast Discussion NWS Weather Prediction Center College Park MD 400 AM EDT Wed Aug 19 2026 Valid 12Z Wed Aug 19 2026 - 12Z Fri Aug 21 2026 ...Heavy rain and flash flooding threats across the Midwest, Ohio Valley and southern Arizona today, shifting east to the Mid-Atlantic coast on Thursday... ...Severe storms possible across mid-Mississippi Valley today through tonight... ...Dangerous heat persists in the South while building into the Southwest... A cool air mass arriving from southern Canada will push a cold front across the northern tier states over the next couple of days. The focus of heavy rain and severe thunderstorm potential will be near the northern boundary of a persistent heatwave across the southern U.S. ÂClusters of organized heavy showers and thunderstorms will continue traveling eastward across the central Plains toward the mid-Mississippi Valley this morning. ÂThese heavy rain and thunderstorms are forecast to become more focused in the vicinity of the mid-Mississippi Valley later today through tonight ahead of a low pressure wave traveling eastward along a meandering front as the cold front from Canada dips southward toward the Midwest. SPC has a slight risk of severe thunderstorms across the mid-Mississippi Valley today while WPC has a slight risk of excessive rainfall extending farther north into the Midwest and Ohio Valley. By Thursday, the cold front from Canada will advance farther east and begin to merge with the meandering front to the south. A convergence zone sandwiched between this pair of fronts will focus a corridor of enhanced rainfall. Heavy rain with embedded thunderstorms is possible 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 on Thursday when daytime heating is maximized. By Thursday night 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. 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. 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 Graphics available at https://www.wpc.ncep.noaa.gov/basicwx/basicwx_ndfd.php $$