Hail has pummeled parts of the central United States in recent weeks, with no signs of letting up: Baseball-sized chunks of ice caused damage in parts of Colorado on Thursday, after DVD-sized hail crashed down in Texas earlier this week.
Hail that was at least the size of golf balls was observed across the Denver region, over an area home to some 1 million people, 9News meteorologist Chris Bianchi estimated. It could be the fourth hailstorm to hit the area with at least $1 billion in damage since 2017.
“It has not been a quiet hail year,” said Andrew Heymsfield, a senior scientist at the National Center for Atmospheric Research in Boulder, Colo.
Meteorologists said such frequent hail storms are to be expected at this time of year, when spring warmth fuels severe weather. But there are some factors making them more damaging than ever, experts said.
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Warming temperatures may be, in effect, making hailstones larger, while also perhaps diminishing the likelihood of smaller hail. And the spread of population across the country means it’s more likely those hailstones fall on structures or vehicles, causing damage.
“It’s going to be a very painful year for insurers,” said Victor Gensini, an associate professor at Northern Illinois University. “When the bull’s eye starts getting bigger, you’re going to start hitting it more.”
Hailstones may be getting larger
Hail is the product of towering thunderstorm clouds whose strong updrafts allow ice to build up and thicken before falling to the ground. Hailstones start as ice pellets known as graupel and develop more frozen layers as the updrafts toss them high up in the atmosphere and they encounter droplets of ice-cold moisture that just keeps accumulating.
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As temperatures warm along Earth’s surface, those updrafts may be getting stronger — and that may allow hail to grow larger before the winds can no longer keep it aloft.
The warmer the air, the more moisture it can hold. And when thunderstorms develop, a greater contrast between hot, moist air close to the ground and cold, dry air overhead can supercharge the upward winds needed to produce hail.
“If it’s very humid, that’s like the gasoline you need for these updrafts,” Gensini said.
Extreme abnormal warmth in the Gulf of Mexico, which sends moisture flowing across the nation’s midsection, is also probably adding fuel to those storms.
“All those things are definitely compounding,” Heymsfield said.
Suburban sprawl makes hail more damaging
Besides the meteorological factors, there are simply more buildings and vehicles in the way of hail storms — the same effect that is increasing damage from severe thunderstorm hazards, including tornadoes.
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But hail accounts for the vast majority of that damage, said Ian Giammanco, lead research meteorologist at the Insurance Institute for Business and Home Safety. Hail damage is behind as much as three-fourths of storm damage costs in any given year, he said.
Severe storms caused a record $60 billion in damage across the United States last year, according to insurance industry data.
As a warming climate spreads conditions prime for large hail, the risks are expanding northward and eastward from the traditional Tornado Alley region and into more populated areas, Giammanco added. Hail that might have only damaged some agricultural buildings a few decades in the past is now landing on sprawling communities.
Questions remain about changing hailstorms
Meteorologists say there is still much to learn about how hail forms, and the impact of climate change, in part because of competing factors that could make hail more, or less, prevalent.
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For example, while increasing temperatures and humidity could fuel larger hail, it could also mean smaller pellets are more likely to melt before hitting the ground, Gensini said.
Wind shear — a change in wind speed and direction at varying altitudes — can help to encourage large hail formation. But research suggests climate change is causing wind shear to diminish, which may result in conditions that are less ripe for hail storms, Giammanco added.
Meteorologists including Gensini and Heymsfield have proposed a National Science Foundation-funded project that could help answer some of those questions with observations gathered during next year’s storm season. They plan to use radar systems, unmanned aircraft and laboratory analysis of hail specimens to better understand where and how they form and how much they melt on the way down, Heymsfield said.
The goal is to improve hail forecasting to allow people more time to prepare and reduce damage, he said, such as by parking vehicles in covered garages.
“The reality is these hail storms not stopping — they’ll probably get a little more intense,” Gensini said. “We’re going to see more and more of these billion-dollar hailstorm disasters.”
