The Most Extreme Rainfall in All 50 States

Brian Donegan
Published: June 29,2016

The most extreme 24-hour rainfall totals recorded in each state (Source: NOAA).

After last week's third deadliest flood event in West Virginia history, many are probably wondering how much rain can fall where they live.
(MORE: Flood Event Kills 23, Leaves Thousands Homeless in West Virginia)
The highest 24-hour rainfall totals on record for each state, according to the National Oceanic and Atmospheric Administration (NOAA), may be surprising.
Heavy rainfall and flooding should be taken seriously. Flooding has killed an average of 82 people per year, according to NOAA, making it the second most deadly weather-related hazard over the last 30 years, just behind heat.
(MORE: Over 230 Killed in U.S. From Flooding Since 2015)
Almost half of all flash-flood deaths occur in motor vehicles. You should never drive into flooded areas, as it only takes 18 inches of water to float a typical vehicle.
It is 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.
(MORE: 10 Hurricane Myths Debunked)
The most extreme 24-hour rainfall total on record in the U.S. is 42.0 inches near Alvin, Texas, between 7 a.m. July 25 and 7 a.m. July 26, 1979. This absurd amount of rain was in conjunction with Tropical Storm Claudette.
Surprisingly, that 42-inch amount may actually be a bit low, as the weather observer reported his rain gauge overflowing at the 1 a.m. reading.
The 43 inches of rain from Tropical Storm Claudette is typically acknowledged as the U.S. national record 24-hour precipitation amount, but that value was estimated in a post-storm survey and is, therefore, not used in this analysis.
(MORE: America's Dreariest Cities)
The second highest 24-hour rainfall total on record in the Lower 48 is 32.5 inches, measured at Dauphin Island Sea Lab in Alabama between July 19-20, 1997, and associated with Hurricane Danny. This is the greatest 24-hour rainfall that has been directly observed at an officially-established observation station within the contiguous U.S., though higher "unofficial" totals have been measured like the one in Texas.
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.
(MORE: Five Things to Look for During the Southwest Summer Monsoon)
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.
In the Southeast, the 24-hour rainfall extremes are mainly between 20 and 25 inches. The exception there is South Carolina with a 24-hour extreme of 14.8 inches, observed at Myrtle Beach and associated with Hurricane Floyd on Sept. 16, 1999.
Remember, all it takes is one tropical system or a line of training thunderstorms to put any of these records in jeopardy. Never underestimate the power of flooding and the damage it can cause.