During severe thunderstorms, rising air shoots icy pellets the size of Dippin’ Dots ice cream into the bitter cold of upper atmospheric layers. There, supercooled water freezes onto the small particles to form hail, which then falls when it gets too heavy for the storm’s upward draft.

As climate change warms average global temperatures, hailstones larger than pingpong or golf balls will become more frequent — likely worsening the weather hazard’s already billions of dollars in annual property damage across the country, according to a study published last year in the scientific journal npj Climate and Atmospheric Science.

“Climate change is obviously occurring,” said Victor Gensini, a meteorologist and professor of atmospheric science at Northern Illinois University who led the study. “The question, for scientists, is often: How does that manifest itself (in) these smaller-scale extreme weather perils?”

Insurance companies have reported rising hail damage claims from homeowners due to severe storms. In 2024, roof repair and replacement costs totaled nearly $31 billion across the country, up almost 30% from 2022, according to an April report from Verisk, a risk assessment and data analytics firm. Hail and wind accounted for more than half of all residential claims. 

State Farm is raising homeowners insurance rates in Illinois by 27.2% beginning Aug. 15, according to a filing with the state last month. The rate hike, one of the largest in the state’s history, will affect nearly 1.5 million policyholders. In addition, State Farm is implementing a minimum 1% deductible on all wind and hail losses, raising the out-of-pocket costs for homeowners filing a related damage claim.

State Farm said its Illinois homeowners business has seen “unsustainable” losses in 13 of the last 15 years and cited more frequent extreme weather events such as wind, hail and tornadoes, insufficient premiums to cover claims and the rising cost of repairs due to inflation.

Last year, State Farm customers in Illinois reported $638 million in hail damage, ranking the state second after Texas.

In May, roughly 100 researchers — including Gensini and other NIU scientists — kicked off the world’s largest-ever coordinated effort to study hail in and around the Central Plains. But “we will go wherever the storms are,” he said in a previous interview.

The work is being supported with $11 million from the National Science Foundation and aims to improve forecasts of severe, damaging hail using data collected through technology such as drones, weather balloons, meteorological instruments that measure hailstone size and strike impact, and more. Better detection and prediction would allow people to protect themselves, their property and their livelihoods, preventing millions of dollars in losses.

Between mid-May and the end of June, scientists tracked 28 hail events across 11 states in the Midwest, South and Mountain West. They recorded hail bigger than 3 inches in Colorado, Texas, Montana and South Dakota.

Recent cuts to federal grants from the Trump administration have paused scientific endeavors in many areas, including weather forecasting, but organizers said the NIU-led study was not affected because funding was awarded last summer.

Northeast Illinois has had its share of big hail this year, too. An early spring thunderstorm produced tornadoes and dropped pea-size hail across the area in mid-March; the largest hailstones reported were as big as half dollars in central Cook County. On May 15, 3-inch hail was observed in Livingston County, and 2-inch hail was also reported in northeast Lake County. Batavia was pelted by hail as big as tennis balls during a June supercell.

According to the National Weather Service, for the last 30 years, the Chicago area has averaged 11 days of any size hail per year and two days of significant stones with diameters 2 inches or larger.

In their study, published in August 2024, NIU researchers found that days with severe hailstorms with larger stones will increase most significantly in the Midwest, Ohio Valley and Northeast by at least five days from mid- to late-century.

“Depending on how hard you press the gas pedal — the gas pedal being human emissions of CO2 — that has a really big impact on hail that we see and, ultimately, where it occurs,” Gensini said. “On average, we see bigger hail, more frequent bigger hail, and we actually see less small hail.”

Using a model with high-resolution mapping offered researchers new, more granular insights into the future of individual storms and their hazards compared with the data that traditional global models produce, which Gensini characterized as coarse and grainy.

“It would be like the difference of a cellphone camera from back in the early 2000s compared to what we have now,” said Jeff Trapp, professor of climate, meteorology and atmospheric sciences at the University of Illinois at Urbana-Champaign.

According to Gensini, a warmer climate concentrates more water vapor in the atmosphere, which in turn fuels thunderstorms and makes them more robust — with stronger updrafts that can suspend bigger hailstones.

“Take a hair dryer and turn it up on end, so it’s blowing air straight up,” he said. “It’s pretty easy to suspend a pingpong ball right above that hair dryer. But now, what if you wanted to suspend a grapefruit or a soccer ball? You’re going to need a much stronger updraft.”

Warmer temperatures in the lower atmosphere would also melt smaller hailstones that fall at a slower speed, while really big stones would remain relatively unaffected.

The model used in the study indicated a more than 25% increase in the frequency of large hailstones of at least 1.8 inches if planet-warming greenhouse gas emissions from human activities do not significantly reduce by mid-century. In that same scenario, stones larger than 2 inches could increase by over 75% by the end of the century, and there would be fewer hailstones smaller than a golf ball, or 1.7 inches.

The National Weather Service considers severe any hail bigger than a quarter or with more than a 1-inch diameter. Anything larger than 2 inches can easily damage roads, dent cars and shred crops. Stones larger than 4 inches are called giant hail, and those larger than 6 inches are called gargantuan hail.

Theoretically, the maximum size could be over 9 inches in diameter, like a bowling ball. The largest recorded hailstone in the country fell on June 23, 2010, in Vivian, South Dakota. It had an 8-inch diameter and weighed 1 pound and 15 ounces. The largest hailstone reported in Illinois was about 4.75 inches, the size of a softball, and fell on June 10, 2015, near the village of Minooka, 50 miles southwest of Chicago.

Having researched severe storms, their hazards and their connection with climate change for decades, the U. of I.’s Trapp emphasized the need to study potential changes in hail’s seasonality, too — even though “there’s not really a hail season, but there are times of the year that are more conducive to (it).”

In Illinois, that’s typically during the spring and early summer.

“This is an important question, I think, ultimately, to address,” he said. “For people who do emergency management, as an example, so that they know that in the coming years, maybe the coming decades, there might be an expectation that their activity will be enhanced during an earlier or different time of the year. And we’re seeing that with severe weather in general.”

No matter the changes in hail size and frequency, the NIU researchers noted that the effects of this weather hazard — mainly in the form of losses and damages — will only grow as an increasingly urbanized landscape leaves more people and their property vulnerable to the pelting stones.

Gensini called hail an understudied, “underappreciated” storm peril. According to Verisk, noncatastrophic wind and hail roof claims increased from 17% to 25% between 2022 and 2024, which the company says highlights the growing impact of these perils despite the greater focus often placed on catastrophic events.

“Tornadoes are incredibly dramatic; they can produce casualties and fatalities. You generally just don’t see that with hail; (stones have) impacts (on) assets and structures, and not necessarily people or their livelihood. But the trade-off of that is hail is way more frequent, way more common,” Gensini said. “And because of that frequency, we see way more damage and way more impact, in terms of insured losses from hail, every single year.”

adperez@chicagotribune.com