Excessive Rainfall: Where Does It Most Frequently Occur? | WeatherBug
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Excessive Rainfall: Where Does It Most Frequently Occur?

September 18, 2022
By WeatherBug Sr. Meteorologist, Chad Merrill
Just like the Storm Prediction Center’s assessment on daily severe thunderstorm risks, another branch of the National Oceanic and Atmospheric Administration (NOAA) focuses on the threat for rainfall to trigger flooding. These outlooks provide meteorologists with critical information to relay to the public on the second leading cause of deaths related to weather, flooding.

One hundred and forty-six deaths were attributed to flooding in 2021, just behind heat, which killed more people last year than any other natural disaster. The Weather Prediction Center issues a daily forecast for one, two and three days out that identifies flooding risks for meteorologists to use in relaying important information regarding the flood and flash flood risks in their communities. 

The Excessive Rainfall Forecast is essentially a product that indicates a marginal, slight, moderate and high risk that rainfall will exceed the amount needed to produce flash flooding. May through September is the busiest season for flash flooding since thunderstorms and tropical systems account for the heaviest rainfall during the calendar year. 

A marginal risk means that there is a 5-percent chance for rainfall to trigger flash flooding. A slight risk includes a 15-percent risk for flash flooding, moderate is 40-percent and rare high-risk days include at least a 70-percent chance for flash flooding to occur in a given area highlighted by the Weather Prediction Center.

In the last five years, Texas, Louisiana, Mississippi, Arkansas and Alabama round out the top five states that see the most high-risk rainfall days. From 2016 to 2021, the top five metropolitan areas that statistically see the most high-risk rainfall days include Beaumont-Port Arthur, Texas, Lake Charles, La., Houston, New Orleans and Lafayette, La. A combination of stalled fronts and moisture from tropical systems in the late summer and fall account for the high frequency of flash flooding.

The coordination efforts between the Weather Prediction Center and local National Weather Service offices allow Flash Flood and Flood Watches to be issued ahead of weather events that will likely cause flooding. 

It’s important to keep in mind as the tropical season gears up that six inches of fast-moving water can knock you off your feet and two feet of running water can float a vehicle. Remember to “Turn Around, Don’t Drown,” because water is usually deeper than what it appears.

Stay ahead of flash flooding by downloading the WeatherBug app to get the latest flood alerts for your area. 
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Story Image: The waterfront neighborhood on River Road off of Three Rivers Road in Biloxi, Miss., has flood waters from the rising Biloxi River on Thursday, Aug. 25, 2022. (Justin Mitchell/The Sun Herald via AP)