Heavy Rainfall Discussion: Localized Flash Flood Threat Today Between 3pm and 7pm Across Western North Carolina

Showers and thunderstorms are becoming more numerous across western North Carolina this afternoon, and the environment is becoming increasingly favorable for localized heavy rainfall capable of producing flash flooding through the early evening hours.

As we’ve been watching throughout the day, the atmosphere has become progressively more unstable thanks to daytime heating. Combined with abundant Gulf and Atlantic moisture streaming northward into the Carolinas, this is creating an environment where thunderstorms can produce very intense rainfall in a short amount of time. Precipitable water values remain exceptionally high for early August, meaning the atmosphere is capable of producing very efficient rainfall.

Adding to the concern is a stationary frontal boundary draped across the region, extending near Asheville and eastward across North Carolina. This boundary is serving as a focus for thunderstorm development, while several weak disturbances rotating around an upper-level low over Georgia continue to provide additional lift. Together, these ingredients are expected to support increasing thunderstorm coverage through the remainder of the afternoon.

The greatest concern will be storms that either repeatedly move over the same location or merge together. When this happens, rainfall rates of 1 to 2 inches per hour are likely, with isolated pockets potentially exceeding that for brief periods. Most locations will receive beneficial rainfall, generally between 1 and 3 inches, but isolated areas could see significantly higher totals where storms train or repeatedly redevelop. That’s where the flash flooding could occur.

Not everyone will experience flooding, but the threat is greatest in areas that have received recent heavy rainfall, along small creeks and streams, in steep mountain terrain, and in urban or poor-drainage locations. Water levels can rise rapidly when rainfall rates become this intense, especially in the mountains where runoff accelerates quickly into valleys and streams.

The highest threat window appears to be through around 7 PM, when daytime heating and atmospheric instability will be at their peak. After sunset, storms should gradually begin to weaken, although scattered showers and thunderstorms may linger into the evening.

If you encounter a roadway covered by water this afternoon or evening, remember that it only takes a small amount of moving water to sweep away a vehicle. Never drive through flooded roadways, and be prepared for rapidly changing conditions if thunderstorms repeatedly move across your location.

While this is not expected to be a widespread flash flood event, localized flash flooding is certainly possible anywhere the heaviest storms become slow-moving or repeatedly track over the same communities. We’ll continue to monitor radar trends closely through the afternoon and provide updates if the threat increases.