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When the Sky Falls · The Climate Translation

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Years ago, on a storm chase in the Texas Panhandle,
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I remember standing beneath one of those enormous, Great Plains skies, watching a violent
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supercell move across the open landscape.
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The storm was almost isolated by itself, with large hail and torrential rain.
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Then, we we noticed something different, a dark column beneath the storm began accelerating
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towards the ground.
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It wasn't rotating like a tornado, it was falling.
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When that column reached the surface, it seemed to explode outward, almost like dumping
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a bucket of water onto concrete and watching it spread in every direction.
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What we were watching was a downburst, and new research suggests that environments capable
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of producing damaging downbursts may be becoming more favorable as the climate warms.
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Today we're going to explore what happens when the air doesn't rise inside a thunderstorm,
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but falls.
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Welcome back to the podcast, I'm Dr. Mac, and this is The Climate Translation.
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When we talk about thunderstorms, we usually focus on the air going up.
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Warm human air rises from near the surface.
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As it climbs, it cools, and water vapor condenses into clouds.
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That condensation releases heat, giving the rising air even more energy.
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That rising column of air is the updraft, and in severe thunderstorms, the updraft can
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be incredibly powerful.
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It can carry raindrops and hail stones, thousands of feet upward, and keep them suspended inside
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the storm.
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But eventually, gravity wins.
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As rain and hail accumulate, their weight begins pulling downward on the air around them.
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Meteorologists call this precipitation loading.
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Think about carrying a backpack.
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A few books may not slow you down very much, but keep adding books, and eventually that
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extra weight begins pulling you towards the ground.
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Something similar can happen inside a thunderstorm, but weight is only part of the story.
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As rain falls into a drier air, some of that water begins to evaporate.
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Evaporation requires energy, and that energy comes from the surrounding air.
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The air cools, and cooler air is denser than warmer air.
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So now you have precipitation pulling downward, while colder, heavier air is also beginning
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to sink.
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If hail or other ice particles are melting as they fall, that takes additional energy
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from the surrounding air, and produces even more cooling.
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The downdraft can begin to accelerate, and under the right conditions, it can accelerate
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quickly.
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When that concentrated column of descending air reaches the ground, and then spreads outward,
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with damaging winds, meteorologists call it a downburst.
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If the damaging outflow is less than about 2.5 miles across, we call it a microburst.
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If it's larger, we call it a macroburst, and there are different types.
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A wet microburst occurs when descending air reaches the surface along with heavy rain
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and sometimes hail.
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You may have heard these described in news reports as rain bombs, because from a distance,
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the precipitation can look like a mass of water suddenly dropping out of the storm.
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But rain bomb is not really the scientific term, what you're seeing is a wet microburst.
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A dry microburst works a little bit differently.
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They're very common in places like the Western United States and the High Plains, where thunderstorms
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can develop with very high cloud bases and a deep layer of dry air underneath.
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Rain begins falling from the cloud, but it evaporates before it reaches the surface.
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You may see streaks of precipitation hanging beneath the cloud that never reach the ground.
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MMeteorolgists call that verga.
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All that evaporation cools the air dramatically.
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The rain may disappear, but the down draft is not.
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Cold dense air continues racing towards the ground, producing damaging winds even if
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there's very little rain.
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And there are hybrid microbursts that contain characteristics of both.
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So the basic ingredients can vary from storm to storm.
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Heavy precipitation can help pull the air downward, evaporation and melting can cool it.
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Dry air can make that cooling even more efficient.
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But all of those pathways can lead to the same outcome.
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A column of air that was once suspended inside a thunderstorm begins accelerating towards
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the surface.
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And when it reaches the ground, the vertical wind has to go somewhere.
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When all that air, moving downward at highway speeds reaches the surface, it can't keep
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going.
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The ground stops the vertical motion, so the air spreads outward.
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This is the part of the downburst that does the most damage.
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Think back to that bucket of water I described from that storm chase in the Texas Panhandle.
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If you dump water straight onto a hard surface, it strikes the ground and then immediately
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races away from the point of impact.
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Air is a fluid and acts in much the same way, except now that outward moving air may be traveling
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at 70, 80, even 100 miles an hour or more.
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This is where we get what meteorologists call straight-line winds.
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The name can sometimes make these winds sound less dangerous than a tornado, but they aren't.
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A 90-mile an hour wind does not become harmless because it's moving in a relatively straight
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direction.
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Even though it's not rotating, it can still uproot trees, peel roofing materials from buildings,
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destroy sheds and manufactured homes, topple power lines, and turn loose objects into flying
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debris.
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In extreme microbursts, winds can exceed 100 miles an hour.
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That creates another problem.
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After a damaging thunderstorm moves through, people assume a tornado must have caused
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the destruction.
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I saw this frequently during my years in television weather.
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Someone would call the station and say, a tornado came through my neighborhood, trees
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are everywhere.
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Sometimes they were right, but sometimes when meteorologists looked at the radar and the
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National Weather Service crews surveyed the damage, there wasn't a tornado at all.
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One of the clues is the direction of the debris.
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A tornado is a rotating column of air.
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Near the ground, winds generally flow toward and around that circulation.
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It leaves a converging or chaotic pattern of damage.
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A downburst is different.
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Winds are spreading outward from where the downdraft reached the ground, so trees can be flattened
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roughly in the same direction or fan outward from the center of the burst.
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meteorologists can sometimes walk through a damaged neighborhood, map the direction the
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following trees or pointing, compare that to Doppler radar data, and then reconstruct
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what happened.
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And radar has made us better at recognizing these events.
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On Doppler velocity displays, we can look at how air is moving towards or away from the
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radar.
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Sometimes you can actually watch the winds accelerating downward through the storm and then see the
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outflow expand across the surface.
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But microbursts remain difficult to forecast precisely.
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Part of the problem is their size.
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A damaging microbursts may only affect a neighborhood or a few miles of countryside, and last just
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a few minutes.
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A weather station several miles away may record nothing remarkable.
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Even radar is sampling the atmosphere above the ground at increasing heights as you move
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farther away from the radar side.
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So the most destructive wind can sometimes slip beneath our observing systems.
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That's one reason these storms can feel so sudden.
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The sky darkens, the rain begins, and within a few minutes a wall of wind can move through
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with enough force to flatten trees and damage buildings.
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There may have never been a tornado, but the damage was real.
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And sometimes that burst of cold air doesn't fade away.
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It becomes a starting point for the next storm.
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So we've been talking about individual downbursts, one thunderstorm, one down draft, one burst
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of damaging wind, spreading outward when it reaches the ground.
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But thunderstorms rarely operate in complete isolation.
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And this is where the scale of the problem can grow very quickly.
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Remember that the air inside a downburst is relatively cold and dense.
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When it reaches the ground and spreads outward, it forms what meteorologists call a cold
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pool.
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Along the leading edge of that cold pool is a gust front.
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If you've ever been outside to have a thunderstorm and suddenly felt a cool rush of wind before
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the rain arrived, you probably experienced a gust front.
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That boundary can act like a wedge.
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The colder air pushes underneath the warm human air ahead of the storm and forces it upward.
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And if the atmosphere is unstable enough, that rising air can produce another thunderstorm.
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That new storm creates its own down draft, its own cold pool, and its own damaging winds.
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Now imagine that happening repeatedly along a line.
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Instead of one isolated burst, you begin building an organized system of thunderstorms
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whose outflow reinforces one another.
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As a meteorologist, this is something I've watched many times on Doppler Radar.
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You can see the leading edge of that cold pool racing away from thunderstorms.
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And new thunderstorms begin developing along that boundary.
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The line sometimes starts to bow outward as stronger winds surge to portions of it.
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And under the right atmospheric conditions, the system can rebuild itself for hours.
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One feature that can help strengthen these systems is called a rear inflow jet.
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Despite the name, it isn't the jet stream above us.
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It's a concentrated current of air that can enter a thunderstorm from behind and accelerate
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towards the leading edge.
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That additional push can strengthen the down drafts and the straight line winds moving
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out ahead of the storms.
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When this becomes organized enough and produces a long swath of damaging winds across hundreds
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of miles, meteorologists may classify the storm as a derecho.
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We have seen a couple of excellent examples.
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On May 16, 2024, a derecho moved through southeast Texas and into the Houston area.
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The National Weather Service estimated winds over a hundred miles an hour in some locations.
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Transmission towers collapsed, hundreds of thousands of people lost electricity, and
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in downtown Houston, windows were blown out of skyscrapers.
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The storm eventually became a billion dollar weather disaster.
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And then just this past month, on August 11, of 2026, another derecho crossed portions
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of Illinois and Indiana.
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The National Weather Service in Chicago documented widespread straight line winds between seventy
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and a hundred miles an hour.
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At the Gary/Chicago International Airport, a wind gust reached ninety-nine miles an hour.
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That storm also produced tornadoes.
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And that combination is worth remembering.
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A derecho is not the opposite of a tornado outbreak.
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An organized thunderstorm complex can produce both.
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But across much of the storm, the dominant damage may come from air-moving outward in
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straight lines rather than rotating around a tornado.
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So now we've moved from a burst that might damage a few neighborhoods to an organized wind
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storm capable of crossing several states.
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It's a different scale, but the same basic ingredients.
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Air inside thunderstorms accelerating towards the ground.
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And that raises a question at the center of this episode.
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What happens when the atmosphere itself becomes more capable of producing those powerful
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down drafts?
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It's a climate question we should consider.
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Are these damaging winds becoming stronger as the atmosphere warms?
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For a long time, it was surprisingly difficult to answer.
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Microbursts are small.
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They may only last a few minutes.
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And as we talked about earlier, many of them never passed directly over a weather station.
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But newer high-resolution computer models are finally allowing scientists to examine the
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storms in greater detail.
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In 2023, atmospheric scientists Andreas Prein at the National Center for Atmospheric Research
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studied damaging straight line winds across the central United States.
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He combined weather observations with high-resolution computer simulations capable of recreating thunderstorms
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at a scale of about two and a half miles.
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The results were striking.
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Over roughly four decades, the simulated area affected by damaging straight line winds
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increased nearly fivefold.
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And Prein found that the intensity of those winds increased as the temperature rose.
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To understand why you have to look back at the down draft, remember that downbursts depend
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partially on the difference between the cold air falling from the thunderstorm and the
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warmer air surrounding it.
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As the background atmosphere warms, the contrast can become larger under the right conditions.
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A cold down draft becomes even more negatively buoyant or heavier compared to its surroundings.
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In other words, it wants to fall.
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And it can fall faster.
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Meteorologists have a way of estimating that potential.
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It's called Downdraft Convective Available Potential Energy or DCAPE.
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We've talked about CAPE before in this podcast as a way of estimating the energy available
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for air to rise and fuel a thunderstorm.
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DCAPE looks at the other direction.
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It estimates how much energy may be available for air to accelerate downward.
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And new research suggests that number may be increasing.
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In a study published in the geophysical research letters in early 2026, Ian Williams and
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Gwendolyn Fieweger at Iowa State University used the Community Earth System model to examine
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how downburst environments across the U.S. could change as climate change continues its
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warming process.
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Under a high emission scenario, average DCAPE increased by 5 to 12 percent across most
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of the country by the end of the century.
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And some of the most extreme downburst environments increased even faster.
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Temperature was the largest driver, but changes in humidity and the height where down drafts
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begin also mattered.
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That last part is important.
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A warmer atmosphere can hold more water vapor, which can provide thunderstorms with more
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moisture and energy.
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But in some environments you can also have dry air beneath the storm or higher cloud bases.
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When rain and hail fall through that dry air, more evaporation can occur.
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More evaporation means more cooling.
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More cooling means denser air, and that strengthens the down draft.
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So climate change is not simply adding one ingredient to thunderstorms.
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It's changing several parts of the environment at the same time.
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And the effect is not identical everywhere.
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Some regions may be more favorable for damaging downbursts than others.
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Some seasons may change more than others.
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In fact, Williams and Fieweger found particularly large increases and some extreme winter downburst
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environments across the Midwest.
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That means the risk may simply not grow, it could shift geographically and seasonally.
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And this is why scientists are paying much more attention to straight line winds.
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For decades, tornadoes have received much of the attention when it comes to severe thunderstorms.
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But in a warming atmosphere, the wind falling out of those storms may deserve our attention
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as well.
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When we think about severe thunderstorms, tornadoes get most of the attention, and understandably
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so.
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But a storm doesn't have to rotate to be dangerous.
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Downbursts can strike neighborhoods with hurricane force winds, flatten trees, damage buildings,
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and knock out power within a few minutes.
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And when thunderstorms work together, the winds can spread out across regions.
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Evidence is suggesting that as the atmosphere warms, the environments that support these
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damaging downdraft are becoming more favorable.
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That means forecasting is important.
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And we need a better understanding of what a severe thunderstorm warning can actually
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mean.
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Because sometimes the greatest danger in a storm is not the air spinning beneath it, it's
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the moment that the sky itself seems to fall.
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I'm Dr. Mac, and this has been the Climate Translation.
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If you have a question about the climate you've been too afraid to ask, or if you have
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a differing opinion, I want to hear from you.
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I can use your viewpoints in future episodes.
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You can reach me at theclimatetranslation at gmail.com.
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I'll see you next time.