How Does Hail Form Inside a Thunderstorm?

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Hail can fall in a few minutes during a thunderstorm and leave stones on lawns and garden beds. Hail is ice that forms inside thunderstorms, and its formation depends on strong upward air currents. The answer to how does hail form inside a thunderstorm comes down to three steps: an updraft lifts water into freezing air, supercooled droplets freeze onto the growing ice, and the stone falls once it becomes too heavy for the updraft to hold. This explainer follows that sequence and notes what the sources leave unresolved.

Quick answer

Hail forms when updrafts in a thunderstorm carry raindrops high into very cold air, where they freeze.
Hailstones grow by colliding with supercooled water drops, which stay liquid below freezing until they touch ice.
The stronger the updraft, the longer a stone can grow and the larger it can become.
A stone falls when it is heavy enough to overcome the updraft or when the updraft weakens.

Step one: an updraft lifts water into the cold

Hail begins with water that is carried upward. The University of Illinois Extension hail page, which draws on the National Severe Storms Laboratory, says hail is a form of precipitation that occurs when updrafts in thunderstorms carry raindrops upward into extremely cold areas of the atmosphere, where they freeze into balls of ice. The NOAA JetStream page says the same thing with slightly different wording: updrafts carry raindrops upward into extremely cold areas of the atmosphere.

The updraft is the engine of the process. Without rising air strong enough to lift water high into the cloud, raindrops fall as rain before they reach the freezing layer. Both sources treat the updraft as the central feature of a hail-producing storm, not a side detail.

Step two: supercooled droplets freeze onto the stone

High in the cloud, water can stay liquid well below 32 degrees Fahrenheit. The Illinois Extension page calls these supercooled drops and explains that they freeze on contact with ice crystals, frozen raindrops, dust or other nuclei. NOAA describes the same condition as liquid drops surrounded by air that is below freezing, which is common in thunderstorms.

A hailstone starts as a small piece of ice, which NOAA calls the nucleus. The stone grows when it collides with supercooled drops. NOAA describes two ways this happens. In wet growth, the air is just below freezing, and liquid water spreads across the tumbling stone and freezes slowly. Air bubbles escape during that slow freezing, so the layer is clear. In dry growth, the air is well below freezing, and the drop freezes at once, trapping air bubbles. That layer looks cloudy. The alternating clear and cloudy layers are what give hail its layered look.

The growth is not a single trip. The Illinois page says hailstones can travel up and down in an updraft, and the number of layers can show how many times a stone reached the top of the storm. The page also says hailstones can begin to melt and then refreeze together, forming large, irregular ice.

Step three: the updraft holds the stone, then lets go

The stone keeps growing while the updraft holds it up. The Illinois page says the hail falls when the thunderstorm’s updraft can no longer support the weight of the ice or the updraft weakens. It also states that the stronger the updraft, the larger the hailstone can grow. A storm with a strong updraft can therefore produce larger stones than a weaker storm, all else being equal.

NOAA adds a detail about the storm’s structure. In supercell thunderstorms, strong updrafts create a rain-free area called a weak echo region, which suspends rain and hail aloft and produces a strong radar echo. The hailstone is carried up by the updraft and grows as it collides with supercooled drops and other small pieces of hail. A stone can also be blown out of the main updraft and begin to fall, or be pulled back into the cloud for more growth.

Wind affects the fall. The Illinois page says hailstones bump into raindrops and other hailstones inside the storm, which slows their fall. Drag and friction also slow the fall. Strong winds can push hail so that it falls at an angle.

Why some regions get more hail

Florida has the most thunderstorms, but it does not have the most hail. The Illinois page says Nebraska, Colorado and Wyoming usually have the most hail storms. NOAA names New Mexico, Colorado and Wyoming in the same role. Both sources explain the difference through the freezing level, which is the height in the atmosphere where temperatures reach 32 degrees Fahrenheit or below.

In Florida storms, the freezing level is high, so hail often melts before reaching the ground. In the high plains, the freezing level sits much closer to the ground, so stones have less time to melt on the way down. The Illinois page calls the area where Nebraska, Colorado and Wyoming meet “hail alley” and says it averages seven to nine hail days per year.

How we chose these sources

This article uses two sources. The University of Illinois Extension page is a university extension resource that summarises the National Severe Storms Laboratory material. The NOAA JetStream page is an official U.S. government page on thunderstorm hazards. Both pages were opened on 2026-10-27, and the quotes come from the text returned on that date. Both sources agree on the basic process, which is why the explanation here relies on them together.

The article does not add figures beyond those in the sources, and it does not cover hail damage or hail protection because neither topic is part of the formation question. For other weather-driven stress on plants, see why frost ruptures plant cells and how tree branches break under snow load.

What we could not verify

The sources explain the formation process clearly, but several details are not covered. The list below separates what the sources say from what they leave open.

What the sources do not say

The sources do not give the typical size of hailstones for a given updraft speed, so the link between updraft strength and stone size is described only in general terms.
The sources do not explain how the freezing level is measured for a particular storm or date.
The sources do not give the sizes of supercooled drops, the rates of collision, or the time a stone spends in the cloud.
The sources do not say how often hail forms in a particular county or garden, so no local frequency can be estimated.
The sources do not describe how hail affects plants, soil or garden structures, so no claim about damage is made here.

Frequently asked questions

Why does hail form in summer thunderstorms?

Both sources describe hail as forming in thunderstorms with strong updrafts. The sources do not single out a season, but they do explain that the freezing level must be high enough in the cloud for water to freeze, which is part of why the high plains are favored.

Can hail form without a thunderstorm?

The sources describe hail as forming in thunderstorms, where updrafts carry raindrops into freezing air. They do not describe hail formation in other kinds of cloud, so no other pathway is claimed here.

What do the layers in a hailstone show?

The Illinois page says one can tell how many times a hailstone traveled to the top of the storm by counting the layers. Layers form when a stone alternates between wet growth and dry growth during its trips through the updraft.

Why does a storm drop hail after the updraft weakens?

The Illinois page says hail falls when it becomes heavy enough to overcome the updraft, or when the updraft weakens and can no longer support it. Either change lets gravity pull the stone toward the ground.

Why does hail sometimes fall at an angle?

The Illinois page says strong winds can blow hail so that it falls at an angle. The sources do not describe how common this is in any particular storm.

Sources

University of Illinois Extension, “Hail,” Weather Phenomena, https://extension.illinois.edu/weather/hail (opened 2026-10-27)
NOAA JetStream, “Thunderstorm Hazards: Hail,” https://www.noaa.gov/jetstream/hail (opened 2026-10-27)