5 Reasons The US Is Heading Into The Most Dangerous Time For Flash Flooding

Yard Flooding Problem? These Plants Can Help

We are heading into the peak time for an often overlooked danger in the U.S: flash flooding.

Although this threat doesn't typically grab headlines as much as tornadoes and hurricanes, you should take it just as seriously, especially since prolific rainfall rates are more common as we get into late spring and summer.

Big Picture

First, What Is A Flash Flood? Floods of this type are typically short-fuse events triggered by heavy rain over a relatively small area. For example, a thunderstorm producing 8 inches of rain in a localized area in just a few hours might trigger a flash flood that comes and goes quickly. That's different than longer-duration river flooding events taking place over days or weeks.

Peak Time Is Late-Spring And Summer: While it can happen any time of year, about 75% of flash flood reports between 2007 and 2017 happened from late April through mid-September, according to NOAA's Weather Prediction Center (WPC).

Deeper Dive

The reason for this peak in flash flood reports can be explained by five key factors:

1. Warm, Humid Air Is Most Abundant: More water vapor can exist in warmer air, which increases the rainfall potential for both individual thunderstorms and larger-scale weather systems in many parts of the country.

2. Jet Stream Slows, Moves North: This means winds that steer both weather systems and thunderstorms are lighter by summer, especially in the central and southern U.S. That causes thunderstorms to move more slowly. The slower the movement, the greater the rainfall potential.

3. Thunderstorm Complexes: Sometimes we see large masses of storms known to meteorologists as a mesoscale convective system (MCS). These can move slowly if winds aloft are weak, which triggers major flash flooding, particularly overnight and in the morning over the nation's midsection.

4. Southwest Monsoon Activates: This adds another region to the fold for possible flooding, especially from July through August and into September. The slow movement of these thunderstorms can flood normally dry washes and arroyos, including in urban areas like Phoenix and Las Vegas.

Why This Matters And How To Stay Safe

Flooding Is Biggest Storm-Related Killer: NOAA says an average of 103 deaths per year (2014-23) have been caused by flooding, more than twice the average of tornado deaths.

Vehicles Are A Danger: When heavy rain threatens, never try to drive through a flooded road. Driving contributed to 36% of the 181 flooding deaths in 2024 and 54% of the 78 flooding deaths in 2023.

It may be tough to tell how deep the water is when you approach a flooded section of road, especially at night, so never try to proceed – instead, "Turn around. Don't drown," as the National Weather Service says. Entering a flooded area can allow water to enter your vehicle in a matter of minutes or even seconds.

(MORE: Your Vehicle Can Be A Trap In A Flash Flood)

Take Warnings Seriously: Your local NWS office issues a flash flood warning when flash flooding is either already happening or expected to develop based on rainfall rates and radar trends. You should make sure you are aware of possible flooding in your area when one is issued and avoid travel if possible, especially at night.

If a flash flood emergency is issued, that's your signal that the situation is dire and you should avoid travel and head to higher ground if in a flood-prone location.

(MORE: 4 Things To Know About Flash Flood Emergencies)

Chris Dolce has been a senior digital meteorologist with weather.com for nearly 15 years after beginning his career with The Weather Channel in the early 2000s.