Nighttime thunderstorms can be more unpredictable than hurricanes. And they can be just as fierce, unleashing flash floods, violent winds, and thousands of lightning flashes within minutes.
The storms often stretch across entire states and have caused billions of dollars in damage and killed hundreds of people in the United States in recent decades. They've wreaked similar havoc in southeast Asia, northern Australia, and sub-Saharan Africa.
And yet how nighttime thunderstorms form remains a mystery. Unlike daytime thunderstorms, which are fairly well understood, forecasters still struggle to predict when a nighttime thunderstorm will spawn severe weather. Meteorologists know where the storms will form but not, for the most part, how bad they'll get.
Clear blue skies can give way to a nighttime thunderstorm cluster that's producing widespread heavy rainfall and high winds in a matter of hours, says David Imy, a forecaster with the National Severe Storms Laboratory in Norman, Oklahoma.
But these storms aren't all bad. They provide life-giving rain for ecosystems and for the American breadbasket, delivering between 30 to 70 percent of the U.S. Great Plains' rainfall in the warm months.
The ability to predict a nighttime storm could help residents in a particular locale prepare for the worst—and help farmers gauge whether or not their crops will get enough water.
So Imy and about 200 other scientists, graduate students, and undergrads have descended on this sleepy central Kansas town for six and a half weeks to start decoding the storms' secrets. They are part of the Plains Elevated Convection at Night project, a $13.5-million effort that's financed by the National Science Foundation, the National Oceanic and Atmospheric Administration, NASA, and the U.S. Department of Energy.
The scientists hope that taking detailed observations of atmospheric conditions before and during nighttime thunderstorms will help meteorologists better predict where high winds will form and where heavy rains will fall.
But about halfway through the study, near the end of June, Kansas sits baking at 99°F (37°C) under nearly cloud-free skies.
Six-wheeled flatbed trucks modified to carry Doppler radars sit idling in parking lots, their dishes staring blankly at a blue sky while weather balloons stay packed inside of cases. Pilots tasked with collecting data from inside these storms—spiraling in and out of thunderclouds—instead get yet another night to watch movies on their tablets.
In addition to being unpredictable, it turns out that nighttime thunderstorms can be pretty elusive.
"The joke in our field is that if there's some weather phenomena that you want to suppress, just plan a field project to go study [it]," says Russ Schumacher, an atmospheric scientist at Colorado State University in Fort Collins and one of the Kansas project's leaders.
One big reason nighttime thunderstorms remain an enigma is because all the action happens in a layer of the atmosphere that we can't easily observe.
Daytime thunderstorms are driven by sunlight that heats the Earth's surface. Warm, moist air rises through the atmosphere and encounters colder air. The warm air cools, water condenses to form rainclouds, and the cold air sinks towards the ground.
This sets off an up-and-down cycling of air that, if it goes on long enough, becomes a thunderstorm. There's so much energy built up in these storms that some of it lashes out as lightning and thunder. (See 13 striking pictures of extreme weather.)
The basic ingredients of a nighttime thunderstorm are the same as a daytime storm. But where and how those ingredients mix is very different.
At night, the layer of air next to the ground is relatively cool and stable. So nighttime thunderstorms form in an active region above this stable layer, roughly 1,640 to 3,300 feet (500 to 1,000 meters) off the ground—about two to three times the height of the Eiffel Tower.
Since nighttime thunderstorms can't get their fuel from warm, moist air rising from the Earth's surface, they require a river of air called a low-level jet to bring heat up from the Gulf of Mexico. Atmospheric ripples called bores likely play a role in maintaining these storms once they get going, although scientists are still trying to understand just how that happens.
These complex air currents somehow come together to herd smaller thunderstorms into a huge cluster that acts like one giant system—the nighttime thunderstorm, or what scientists call a mesoscale convective system.
These clusters sometimes form out of thin air, says Tammy Weckwerth, an atmospheric scientist with the National Center for Atmospheric Research in Boulder, Colorado. And even minor changes in atmospheric temperature can make the difference between the initiation of a big storm or the continuation of an uneventful night.
Because all these changes occur above the atmospheric layer that's regularly sampled by weather stations, scientists have had to get creative about how to study them.
So they've come to Kansas with an arsenal of instruments. It includes two stationary and seven mobile radar arrays—Doppler radar dishes welded to the backs of heavy-duty trucks. Scientists can move the dishes to wherever they need to catch a nighttime thunderstorm.
The teams also have a handful of mobile weather stations: Minivans and pickup trucks outfitted with sensors that record air temperature, humidity, and wind speed.
Of course, all this equipment is useless without a nighttime thunderstorm to study.
Which is why, after several days of clear skies, forecasters like the National Severe Storms Laboratory's Imy start looking further and further away from Hays for the telltale angry red splotches blooming on their Doppler radar screens.
Finally, on the fourth Tuesday in June, it looks like nighttime thunderstorms are sprouting over Nebraska and Iowa.
The storms are outside the boundaries outlined by project leaders—a circle roughly 373 miles (600 kilometers) across that cuts through Hays. But at around 3:30 p.m. central standard time, scientists in a conference room at Fort Hays State University decide to dispatch three weather balloon teams, two mobile weather stations, and several mobile radar trucks.
Crews scramble to pack long pants, rain jackets, and toiletries—plus their equipment—in 20 minutes before shooting out of a university parking lot. They have four hours of driving past fields and over dirt roads before they can set up their instruments.
Stacey Hitchcock, an atmospheric sciences graduate student at Colorado State University, forgets to pack long pants. But her team remembers a hand-held vacuum cleaner to suck up the hummingbird-sized mosquitoes that invade their minivan every time someone opens a door.
They will need to stay out until 2 or 3 in the morning, after driving for hours and crossing into Nebraska, to get an accurate picture of the atmosphere before it spawns a nighttime thunderstorm.
Calm Before the Storm
Hitchcock and her teammates end up on the same tan dirt road between two farm fields as the crew of a "Doppler on Wheels," or DOW, from the Center for Severe Weather Research in Boulder.
Their mission: Collect atmospheric data before the formation of a nighttime thunderstorm. With the DOW's generator chugging in the background—and hundreds of fireflies blinking nearby—Hitchcock and her teammates prepare to send up a weather balloon into a deep-purple evening sky.
It's a calm night, so only one person needs to hold the helium-filled white balloon while a second person readies the instruments it will carry aloft. But during a nighttime thunderstorm, the wind can be blowing so hard that "you'll see launches where five or six people are holding the balloon," Hitchcock says.
On this night, no thunderstorm materializes. But the next night, ground teams drive into Iowa and catch their quarry. The wind gusts so hard that the weather balloon Hitchcock and her team hold before launch is blowing sideways.
The project picked back up after that night: In early July, scientists and students scrambled to squeeze in 11 missions in 13 days. "It's exhausting, being on the road for hours and then staying up all night," Hitchcock says.
But she thinks it's worth it. "I got into meteorology because I'm afraid of storms," she says. "I wanted to make myself less scared by studying them."
It worked, but she still gets antsy if there's a lot of lightning.
Follow Jane J. Lee on Twitter.