Explaining Flash Flood Emergencies

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S​ummer has a reputation for prolific rainfall totals in a short amount of time, and because of that, it's when many states have recorded their most extreme 24-hour rainfall records.

Records for 24-hour rainfall in the United States range from less than 6 inches to more than 4 feet. Those amounts for each state are shown in the map below, which uses data compiled by NOAA's Centers for Environmental Information. The record for Kansas is under review by the State Climate Extremes Committee since the previously posted biggest total of 13.53 inches was found to be an error.

Hawaii has the most extreme 24-hour rainfall total and Texas is second. The Hawaii record was recently set on April 14-15, 2018, when 49.69 inches of rain fell at Waipā Garden on the island of Kauai. The Lower 48 record is 42 inches, set in Alvin, Texas, on July 25-26, 1979, when Tropical Storm Claudette soaked the state.

More than 10 states have set new records this century. In addition to already-mentioned Hawaii, C​olorado, Delaware, Kentucky, Michigan, Minnesota, Nevada, New York, Oregon, South Dakota and Tennessee are other states that have set records since 2001. It's a sign of how climate change is making intense, heavy rainfall events ​more likely.

K​entucky is the most recent state to set a new record – 11.28 inches fell in 24 hours on July 18-19, 2023.

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Regional climates influence the extremity of each state's record. It's no surprise that the states with the most extreme 24-hour rainfall totals are located in the Southeast and along the Gulf Coast, as these are the areas most likely to take a direct hit from a tropical storm or hurricane.

Some of the lowest extreme rainfall totals are in the Northern Plains, Rockies and Great Basin. For example, the most extreme 24-hour rainfall total on record in Utah is only 5.1 inches, the lowest of all 50 states. This is because these areas are well-removed from ocean influences, including tropical storms and hurricanes, and have a rather dry climate overall.

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Most of the Northeast has 24-hour rainfall extremes between 10 and 15 inches, with the exception being Massachusetts at 18.2 inches. Additionally, these extremes generally took place during the summer months or early in the fall.

Chris Dolce has been a senior meteorologist with weather.com for over 10 years after beginning his career with The Weather Channel in the early 2000s.