Flash floods kill more people every year than tornadoes, hurricanes, thunderstorms, or blizzards. And yet, the threat for a sudden onslaught of water doesn’t get nearly as much serious attention as it warrants. We’re in the heart of flash flood season in the United States and these killer torrents can happen with little warning. It’s important to be prepared and know how to stay safe as the storms develop.
Flooding is often a slow-motion disaster. A significant river flood can take days or even weeks to unfold. A flash flood, on the other hand, is a flood that ramps up very quickly. Exceptionally heavy rain can double or triple the height of a river or stream in a matter of minutes. Runoff can exceed the capacity of sewerage systems and flood streets, parking lots, and housing developments.
1) Know What To Look For
Flash flooding isn’t a one-type-fits-all natural disaster. Some flash floods are the result of storms that pop up unexpectedly, while other times we can spot the potential for flash flooding days in advance as a tropical system lumbers toward the coast.
Some Thunderstorms Can Linger For Hours
Thunderstorm training can lead to particularly dangerous flash flooding situations. Training occurs when thunderstorms redevelop one after the other, moving over the same areas for hours at a time. This can result in many inches of rain falling in a short period, quickly overwhelming natural and man-made waterways and leading to flooding in areas that aren’t usually prone to flooding.
This kind of sudden flooding happens quite a bit during the warm season, including a few incidents in just the last few weeks. A persistent line of thunderstorms dropped six to eight inches of rain over Martinsville, Virginia, in just a couple of hours on the evening of May 24. The situation grew dire and the National Weather Service issued a flash flood emergency for the city and its surroundings, warning of the potential for “historic flooding” across the area.
It’s tough to anticipate thunderstorm training before it happens. Even though the region had already seen more than half a foot of rain in the week before the storm, a flash flood watch wasn’t in effect for Martinsville as forecasters hadn’t anticipated storms producing as much rain as the area wound up seeing.
Tropical Systems Are Prolific Rainmakers
Wind gets all the attention when a tropical cyclone is spinning toward shore, but it’s the rain that often causes the most problems.
We’re a month into hurricane season and we’ve already seen four named storms so far this year. NOAA expects favorable conditions for above-average tropical cyclone activity in the Atlantic basin this season.
The greatest threat to life and property during a landfalling tropical system is flash flooding—even many hundreds of miles inland. Slow-moving tropical systems have resulted in historic and deadly flooding in each of the last five hurricane seasons, from category four Hurricane Harvey to an unnamed tropical disturbance in 2016 that produced more than a foot of rain in Louisiana.
Desert Areas Can Flood Under A Clear Blue Sky
Visitors to desert regions don’t often associate these hot and arid climates with a flash flood risk. But the climate and terrain in these areas can lead to some of the most dramatic and dangerous flash flooding during the warm months.
Many small creeks and streams run dry most of the year in the American southwest, filling up only after a burst of heavy rain somewhere along the waterway’s path. The runoff from these downpours can gush many miles downstream and run through areas where skies are completely clear, potentially catching hikers and motorists off-guard if they don’t know flash flooding is possible.
2) Know How To Stay Alert
Even on a day when forecasters don’t explicitly call for a risk of flash flooding, these sudden floods rarely come by complete surprise. Thanks to advanced radar products and better guidance, meteorologists usually issue flash flood warnings with enough lead time for folks in harm’s way to quickly change their travel path or seek higher ground.
Checking the forecast once or twice a day is a fantastic way to keep up with the weather, but it’s critically important to keep an eye on Doppler radar and have a way to receive warnings the moment they’re issued. Downloading a reputable radar app and enabling the wireless emergency alerts on your smartphone are small steps you can take now to stay safe later.
3) Know Where To Go
A significant number of deaths during flash flooding are caused by motorists trying to forge a flooded roadway, only to get stuck and washed downstream. It takes about a foot of moving water to lift a vehicle off the road and carry it away. It’s impossible to know how deep the water is—or even if there’s still a road there!—until it’s too late.
Given the risk, how many different ways do you have to go to work, school, the office, or the grocery store? It’s worth investigating a few different ways around town in case one of the routes floods out during a nasty storm. Attempting to forge a flooded roadway isn’t only dangerous for a motorist and their passengers, but it endangers the emergency crews who have to try to rescue or recover them.