Record hailstone from Vivian, S.D., on July 23, 2010. (National Weather Service)

The author, Bryan Wood, is a meteorologist and operations analyst for Assurant. He provides forecasts and insights that help Assurant anticipate and plan for weather’s impact on clients and policyholders. Wood is based in Springfield, Ohio, and can be found on Twitter.


Monday’s hailstorm in Colorado Springs was a reminder that large hail is very dangerous. Not only can it damage property, but it can also kill wildlife and injure or kill people who do not seek adequate shelter. Along with the immediate danger that can result from hail, damage costs are often the lasting impact of a major hailstorm.

When thinking about the major city with the costliest hail day in U.S. history, places such as Denver, Dallas-Fort Worth, Minneapolis, St. Louis, Oklahoma City or San Antonio probably come to mind quickly for the weather enthusiast, but none of them would be the right answer.

The answer is, oddly enough, Phoenix. Up to baseball-size hail fell across the Phoenix metropolitan area on Oct. 5, 2010. The result was $2.8 billion in damage in 2010 dollars, or about $3.2 billion in today’s dollars.

Although the city sees plenty of storminess during monsoon season, Phoenix is not typically prone to damaging hail storms. This means contractor availability is scarce, compared with areas at high risk for large hail, such as the Plains. In the case of the Phoenix event, some homeowners had to wait more than a year before a licensed contractor was available to repair their roofs.

Costly hailstorms are increasing in the United States, with the average year now accumulating $8 billion to $10 billion in hail damage. Additionally, hailstorms account for 70 percent of insured loss from severe storms. In 2017 alone, there were two $2 billion hailstorms, one in Denver and the other in Minneapolis.

Those two storms were not created the same when it came to damage. In Denver, baseball-size hail fell across the cities and its western suburbs. The hail swath included 159 square miles full of heavily damaged roofs. The Minneapolis storm dropped golf-ball-size hail over its northern suburbs. What made this storm extra costly was that — in addition to damaging roofs — the hail was driven by wind. This caused it to fall at an angle that damaged windows and ripped up vinyl siding, as well.

Why are hailstorm costs escalating?

There are three major factors as to why hailstorms are becoming more expensive.

First, we’re building more homes in vulnerable places. Significant urban sprawl has given hailstorms more targets to hit. Densely packed residential areas that took it on the chin in the Phoenix hailstorms of 2010 were largely farmland 50 years ago.

Hail-prone cities such as Minneapolis, Dallas and Denver have experienced similar growth over that period. The expanding urban sprawl and its connection to larger disasters has been studied extensively by researchers such as Ashley, Strader et al.

Second, homes are increasingly larger in size. Since 1973, the average size of a home has grown by more than 1,000 square feet. Larger homes mean larger roofs and more windows to replace when big hail comes to town.

Around the time that homes began to grow in size, vinyl siding was also invented. It has become increasingly popular over the past 50 years because of its lower cost, and it is now the most popular exterior for new homes. Unfortunately, vinyl siding is also notorious for being shredded by hail as small as quarter. This means even lower-level hail from severe storms could leave a home looking something like Swiss cheese.

Third, the cost of roofing materials continues to rise. The most popular roof covering is asphalt shingles, the price of which rose quickly in the late 2000s alongside the rise in crude oil prices. The decrease in refineries over the past 30 years, with the financial incentive to use oil for fuel — rather than asphalt — leaves the asphalt market undersupplied, as well. In addition, the demand for asphalt can rapidly increase after a few major storms of any type, exaggerating the undersupply and further increasing the price.

A next step in hail research

The first North American Workshop on Hail and Hailstorms will convene in Boulder, Colo., later this month. The workshop is set to discuss the rising costs of hail damage, and 200 experts from the fields of meteorology, engineering, economics and climatology will attend. For the first time, these experts will be able to work together to discuss how we can better detect hail, the microphysics and dynamics of hailstorms, the cost of damage and how to mitigate it, and the likely effects of a changing climate on hailstorms.

The conference will play a vital role in moving the conversation forward surrounding hailstorms, including looking at innovative approaches to researching, predicating and mitigating their impact.

The average person may not be aware of the amount of damage hail causes. Hail damage is often not as visceral or emotional as floodwaters inundating a home, a hurricane peeling back a roof or a tornado reducing dwellings to piles of splinters. Instead, hail damage can be sneaky. Some people may not even realize their roofs have been damaged. Over time, the weakness in the roof may allow rainwater to intrude and damage insulation, electrical systems and drywall. If undetected, severe cases can also cause mold to develop.

As our exposure to hail damage grows along with our expanding population, professionals in the field will continue to help make society less vulnerable and more resilient.

Read more:

Violent hailstorm kills rare African vulture brought to the U.S. to help save the species

‘Scariest flight of my life’: Hail smashes nose of plane that flew into towering storm

Models are terrible at forecasting hail. These scientists are working to fix that.