Every year in the summer, a large part of the country braces for hail. Known as Hail Alley, the region stretching from Wyoming to Texas gets more hailstorms and more severe, compared to other parts of the country.
Features on land and in the atmosphere provide perfect hail conditions for this part of the U.S. But living in the hail sweet spot can get uncomfortable.
"My car is the second year I've been here really reared," said Sam Childs, a researcher at Colorado State University. Then "I decided I would like to have a look at hail," he says.
Damaged vehicles are one of the many consequences of severe hailstorms. That's why researchers are trying to improve weather forecasts to better predict when and what kind of icy disturbance might come. The skill may become more valuable over time as climate change makes hailstorms more common in the area.
The Sweet Spot
In order for hail to hit the ground, there must first be a thunderstorm with strong updrafts. These updrafts push falling raindrops backward into the atmosphere until it gets cold enough for water to freeze. Like a ping-pong ball floating above an air vent, the ice pellet falls and is carried high over and over by the upward wind. The ice collides with other water droplets in the clouds along the way, forming frozen layers and growing in size until it becomes too heavy for the wind to keep rising and it falls to the ground.
Although Hail Alley sees ice falling relatively often, thunderstorms across the country form tiny balls of ice all the time, says Katja Friedrich, an atmospheric scientist at the University of Colorado at Boulder. But in most places the air is too warm to keep the ice intact. It melts somewhere between the last drop from the cloud and the ground. "Hail was created during Florida thunderstorms and even hurricanes," says Friedrich. "But the problem is that this area is so hot that the hail barely reaches the [ground] or reaches the [ground] in very small pellets."
In Hail Alley, conditions are cold enough to keep the ice solid. In addition, much of the area is higher, says Friedrich. For example, land in Colorado's High Plains is closer to the source of the hail and gives ice pellets less time and space to melt before coming into contact with the ground. The region is preparing for hail in the spring when warm air from the south and cold air from the north come together, creating perfect conditions for thunderstorms.
Looking to the future
Since every thunderstorm is unique, so is every hailstorm. And about five years ago, the National Weather Service contacted Friedrich to see if it could help track a particular icy variable: how much hail had accumulated on the ground.
Storms in Colorado sometimes dump huge amounts of tiny ice pellets, just like snow. In some cases, so much hail will cover the roads in a short period of time that cities will have to remove snowplows that have already been put away for the season to clean the streets.
Municipalities can ideally anticipate and prepare for these hailstorms. So Friedrich and her research team went looking for data on how much hail accumulates during different storms – a project they are still working on – and build prediction models that predict in the short term whether hail could fall and what it would look like. The work is still in the early stages.
"The more we investigate, the more questions we have," says Friedrich. While the team knows many of the influential factors – such as the amount of moisture in the clouds or how fast the storm is moving – converting those observations into a model that predicts what a result might be is a challenge.
As Friedrich and her team smooth out the details of predicting upcoming hailstorms, Childs looks further ahead. Knowing what these storms might look like further in the future can help shape policies designed to deal with their damage – for example, how insurance companies deal with damage or what farmers can expect from ice-covered crops.
A changing climate
Childs and other researchers have found that climate change could increase hail storms in the coming decades and drop larger ice pellets in Hail Alley. For example, a study Childs co-authored predicts three extra days of hail per year come 2100.
This shift seems likely because some major hailstorm influences will become stronger and more frequent over time. First one warming atmosphere will evaporate more moisture in the air. Increasing the amount of water during thunderstorms may make them more likely to develop hail, Childs says.
Research also suggests that updrafts from thunderstorms could get stronger in an increasingly warmer climate, increasing hail and keeping the atmosphere high enough to be cold enough. Thus, larger chunks of ice are more likely to make it all the way to land, increasing the likelihood that a given storm will drop large chunks of ice.
These predictions do not apply throughout the US and depend on calculations of future atmospheric conditions that may not materialize. For example, if lower levels of the atmosphere become more and more humid, hail could become less of a problem, as higher humidity makes melting more likely, Childs says. And there are caveats in making predictions about future hail events in the West based on data from past storm levels. As the areas became more densely populated over time, so did the likelihood that anyone could even get into a hail storm and report the event.
Regardless, hail research has received attention in recent years. And maybe that's because the storm impacts have a range of damaging effects, from large hailstones wrecking car windshields to tons of tiny pellets clogging storm drains and causing flooding, like the 2018 storm. killed animals and injured personnel at a zoo in Wyoming. As Childs puts it, "I think people realize how dangerous hailstorms can be."