Ice Fall

Introduction

If you have spent any time in the Great Plains during the spring, you learn pretty quickly to respect severe thunderstorms. Back in my twenties and thirties, I spent many Mays traveling across the area studying and chasing storms. Like most meteorologists, I was fascinated by tornadoes. But one of the most memorable moments of my career did not involve a tornado at all.

I was riding in a university research van while we tracked a severe thunderstorm. We thought we were in a relatively safe position. Then the rain suddenly stopped, the sky turned an unsettling shade of green, we began to hear the clink and clunk of hail, and before anyone could react, a softball-sized hailstone came crashing through the window of the van. Fortunately, no one was seriously injured. But staring at that chunk of ice on the floorboard, I remember thinking about how remarkable it was that a thunderstorm could suspend something that large in the air long enough for it to grow.

How does a storm create a piece of ice the size of a softball? And what happens to that process when the atmosphere itself begins to change? Today, we are going to explore the science of hail, how these destructive ice stones form inside thunderstorms, and what new research is revealing about how a warming climate may be changing where and when some of the world's most severe hailstorms occur. Welcome back to the podcast. I'm Dr. Mac, and this is The Climate Translation.

The Atmospheric Escalator

To understand why scientists are interested in how climate change might affect hail, we first need to understand how hail forms in the first place. It all starts inside a thunderstorm. Most people think of hail as frozen rain, and while that is not entirely wrong, it does not really explain how you end up with a piece of ice the size of a golf ball, a baseball, or in rare cases, a softball. For that, we need to talk about what is happening inside the storm itself.

I often tell my students to think of a severe thunderstorm as a giant atmospheric elevator, or maybe more accurately, an escalator. On a hot summer day, the Sun heats the ground. The air near the surface becomes warm and humid, and because warm air is less dense than cooler air, it wants to rise. If the atmosphere is unstable enough, that rising motion can become incredibly powerful. Meteorologists call the fuel for this process Convective Available Potential Energy, or CAPE. You do not need to remember the acronym; just think of CAPE as the amount of fuel available to launch air upward through the atmosphere. The more heat and moisture available near the surface, the larger the fuel tank becomes. When that fuel tank gets large enough, air can shoot upward at remarkable speeds, with updrafts in some severe thunderstorms exceeding 100 miles per hour.

Now let's go back to our hailstone. Imagine a tiny raindrop being carried upward inside one of these powerful updrafts. As it rises higher into the storm, temperatures eventually drop below freezing and the raindrop freezes. At that point, gravity tries to pull it back toward the ground, but the updraft has other ideas. Instead of falling all the way back to Earth, the tiny ice pellet gets caught in that atmospheric escalator and pushed upward again. As it moves through the storm, it collides with supercooled water droplets, which are liquid water that exists even though the temperature is below freezing. Those droplets freeze onto the surface of the hailstone layer by layer and trip after trip. The hailstone grows larger and larger as it continually falls and then is pushed upward again.

If you have ever seen a large hailstone cut in half, it often looks a little bit like the cross section of a tree, displaying rings and layers that formed during repeated journeys up and down through different parts of the storm. This is where the physics becomes surprisingly simple: the stronger the updraft, the larger the hailstone can become. A small hailstone can be supported by a relatively modest updraft, while a baseball-sized hailstone requires a much stronger one. The softball-sized stone that came through the window of our research van all those years ago required an extraordinarily powerful thunderstorm capable of keeping that chunk of ice suspended long enough to grow before gravity finally won.

In many ways, hail is a balancing act between two competing forces: gravity trying to pull the ice downward, and the storm trying to push it back up. As long as the storm keeps winning, the hailstone keeps growing. But what happens when the environment that these stones form in begins to change? Human-induced climate change is not only affecting temperatures at the ground; it is also changing the dynamics of the upper layers of our atmosphere and the potential energy available when thunderstorms form. That means it can influence the physics of the hail equation in surprising ways.

The Goldilocks Zone

At this point, you might think the connection between climate change and hail would be straightforward. After all, hail is made of ice, so if the atmosphere gets warmer, shouldn't hail simply become less common? For years, many people assumed exactly that. But the reality turns out to be much more complicated because hail exists in what we might call a meteorological Goldilocks Zone where conditions must be just right.

Think back to the atmospheric escalator we talked about a moment ago. A hailstone needs a powerful updraft to lift it high into the storm and keep it suspended long enough to grow. A warmer atmosphere can actually help with that because warmer air holds more water vapor, more water vapor means more fuel for thunderstorms, and more fuel often means stronger updrafts. At first glance, that sounds like good news for hail. But there is another side to the equation: our hailstone only exists because part of the storm is below freezing.

As the atmosphere warms, the altitude where temperatures reach freezing begins moving higher into the sky. Meteorologists call this the freezing level, and you can think of it as the storm's ice maker. In a warmer climate, that ice maker gets pushed farther upward. Now our hailstone faces a new problem: once it leaves the storm, it has a much longer journey through warm air before it reaches the ground. Small hailstones may melt completely before they ever arrive, while others may shrink significantly during their descent.

So now we have two competing forces. A warmer atmosphere can create stronger thunderstorms capable of growing larger hailstones, but that same warmer atmosphere can also make it harder for hail to survive the trip to the surface. One process favors larger hail, while the other favors more melting. For decades, scientists were not entirely sure which effect would dominate, making hail historically one of the more difficult severe-weather hazards to project in a changing climate. The atmosphere is essentially pulling the system in two different directions at the same time. But thanks to improvements in computing power, satellite observations, and high-resolution climate modeling, researchers are finally beginning to untangle that puzzle, finding that the favorable environment for hail may be shifting dramatically rather than simply disappearing.

The Moving Target

If a warmer climate strengthens some parts of the hail-making process while weakening others, what does the overall picture look like going forward? The answer researchers are finding is not what many people expected. A recent study published in Nature suggests that hail is not simply becoming more common or less common everywhere; instead, the environment that favors severe hail appears to be shifting.

To understand what that means, imagine that hail has a preferred neighborhood where all of the ingredients happen to line up just right. You need enough warmth and moisture near the surface to generate strong updrafts, which is that CAPE or fuel we talked about earlier. You need cold enough temperatures higher in the atmosphere to support ice formation. You need enough wind shear, which separates the warm updrafts from cooler downdrafts and generates rotation, to organize the thunderstorm. And you need all of those ingredients to exist simultaneously.

Historically, some of the best neighborhoods for hail have existed in places like the Great Plains of the United States, parts of Argentina, South Africa, Europe, and portions of Australia, giving these regions reputations as hail hotspots. But the new research suggests those neighborhoods may be changing. As temperatures continue to rise, many regions closer to the subtropics are projected to see conditions become less favorable for frequent hail formation. At the same time, areas farther poleward may begin experiencing more of the atmospheric ingredients that support severe hail. In other words, the sweet spot appears to be moving poleward across multiple regions.

The researchers also found that these changes are not just geographic; they may also be seasonal. In some regions, the timing of hail-favorable conditions appears to be shifting within the year. That means agricultural areas that have traditionally experienced their highest hail risk during one part of the growing season could begin seeing that risk arrive earlier or later than expected. Timing can be just as important as location, because a hailstorm striking a wheat field a few weeks before harvest can have very different consequences than the exact same storm striking shortly after planting. This is not a forecast for every individual thunderstorm, but an indication of shifting probabilities as the background environment slowly reorganizes itself.

When Risk Moves

What does all of this mean for the rest of us? The most important lesson is that weather risk is not just about intensity; it is also about location. In the Great Plains, where severe weather is common, hail is simply part of the environment that farmers, insurance companies, and builders expect. Nobody likes it, but nobody is surprised by it either, because living in that part of the country means accepting a certain amount of hail risk as part of everyday life.

The challenge highlighted by this new research is that the geography of that risk may be changing. If hail-favorable environments begin shifting poleward, some communities could find themselves dealing with a hazard that historically was not a major concern. Our infrastructure is often designed around the weather we expect rather than the weather we may experience decades from now. Building codes in different regions account for different risks, prioritizing snow loads in some places or hurricane-force winds in others. Communities that rarely experienced damaging hail in the past may not have invested heavily in hail-resistant materials, specialized forecasting programs, or mitigation strategies.

Insurance works the same way by relying on historical records to estimate future risk, but climate change makes the past a less reliable guide for the future. We have already seen this challenge emerge around flooding, hurricanes, drought, and wildfire, and hail represents another example of that broader pattern. Furthermore, much of the technology we are building for the future lives outdoors, including solar panels, electrical substations, transmission lines, wind turbines, vehicles, and glass-clad buildings in densely packed cities. All of them exist exposed to the elements.

Historically, engineers design infrastructure using the local risks they know. If you build in Minnesota, you think about snow and ice; in Florida, hurricanes; and in the Great Plains, tornadoes, wind, and hail. But if millions of dollars are invested in solar installations or infrastructure where severe hail was historically rare, and the probability of hail then increases over time, the initial design assumptions no longer match the operating environment. We are changing not only atmospheric physics, but also the probabilities of when and where specific hazards occur. For regions where severe hail has historically been uncommon, adapting to this shifting risk presents a much steeper learning curve.

Conclusion

A hailstorm depends on a very specific balance of ingredients: heat, moisture, instability, and freezing temperatures high above the ground coming together at the exact right place and time. Climate change is not eliminating these variables, but it is altering their distribution and behavior.

The softball-sized hailstone that shattered the window of our research van all those years ago left an indelible impression on me. It taught me that no matter how knowledgeable or experienced you are, the atmosphere can throw you a curveball. That massive stone was the product of a specific set of atmospheric conditions in a Great Plains storm. As scientists study how these conditions evolve in the decades ahead, it reminds us that if you live in an area that rarely experiences hail, keeping an eye on the sky may become increasingly important in the future.

I'm Dr. Mac. This has been The Climate Translation. If you have a question about the climate that you have been too afraid to ask, or if you have a differing opinion, I want to hear from you. I can use your viewpoints in a future episode. You can reach me at TheClimateTranslation@gmail.com. I'll see you next time.