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Science

What Drives Nighttime Thunderstorms? NOAA And NCAR Hope To Find Out

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Photo by Dave Allen/NIWA
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Courtesy of NCAR
Launching a weather balloon at dusk

June is the start of outdoor recreation season for many Coloradans, and it also marks the start of the peak season for powerful storms and lightning. Colorado's infamous weather unpredictability can suddenly bring afternoon hikes, picnics or games to a quick end.

It's nighttime weather, though, that has atmospheric scientists' attention. They'll be spending six weeks in the Great Plains, trying to figure out the mystery of thunderstorms that form at night. The results could help meteorologists better predict these sometimes damaging storms.The Plains Elevated Convection at Night campaign is a collaboration of the National Center for Atmospheric Research in Boulder and several other institutions, including NASA and the National Oceanic and Atmospheric Administration. It's not your average weather study, according to Tammy Weckwerth, an NCAR scientist and a principal investigator with the study.

"We're hoping to better understand how nighttime thunderstorms form and sometimes grow into these large mesoscale convective systems, [which are] a conglomeration of thunderstorms that can become large and severe," said Weckwerth.

Thunderstorms that form during the day get help from the sun's heat as it warms a layer of air directly above the ground. When that warm air rises it causes circulation of warm updrafts and cooler downdrafts that can create a storm.

Nighttime thunderstorms that develop without solar heating are not as well understood.

"Because the ground is cooler [at night], it creates this stable layer of air near the ground," Weckwerth said. "So all of the circulations in storms at night are elevated above the Earth's surface. And it's this layer of air above the surface that's harder for us to measure."

Nighttime thunderstorms are much trickier to predict than typical afternoon or evening storms. Although they're not necessarily more dangerous than daytime storms, scientists still want to improve forecasting models.

"Large nighttime thunderstorms are an essential source of summer rain for crops – but [they] also produce widespread and potentially hazardous severe weather, excessive rainfall, flash flooding, and unusually frequent cloud-to-ground lightning," said Conrad Ziegler, a research meteorologist at the NOAA National Severe Storms Laboratory.

The $13.5 million campaign will be based in Hays, Kansas, and will cover a large area that includes northern Oklahoma, central Kansas, and south-central Nebraska. More than 100 pieces of technology will play a role, including mobile radar, ground-based instrument suites mounted on vehicles, and several research aircraft – one of which, a NOAA P-3, will be able to fly into the trailing region of storms.

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Credit Image by Alison Rockwell / NCAR/EOL
The PECAN project will deploy more than 100 instruments during the 6-week campaign

Weckwerth said about 250 scientists, instrument technicians, project managers, forecasters and students will participate in PECAN. The sheer number of people and instruments involved is challenging enough, but conducting so much of the research in the dark makes it even more daunting than most studies.

"Not only do we have to worry about safety at night in terms of storms, mobile crews getting back to Hays or to a nearby hotel if it's not feasible to drive back at the end of observations, and the aircraft crew staying out of the severe weather part of these thunderstorms," Weckwerth said. "But also – for people's Circadian rhythms; how do you adjust that without the help of the sun?"

Challenges aside, Weckwerth says she's excited to see the PECAN campaign come together.

"After years of planning, it's exciting to be able to go into the field and collect a data set with this vast array of instruments and wide variety of collaborators from across North America – and start putting together the pieces of the puzzle."

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