SOUTHERN COLORADO (KOAA) — Colorado, Nebraska, and Wyoming are sometimes referred to as Hail Alley. Colorado is one of the most hail-prone states in the country, as the last several weeks have shown!
A lot of you have sent in photos and videos of hail in your communities, and a lot of that hail comes in different shapes and sizes. Those shapes and sizes do more than damage your property; they can also tell you just how strong that thunderstorm that passed through your neighborhood was. They can even tell you about the air mass in the storm and other storm threats.
Storms produce all kinds of different hailstones. Some are cloudy and round. Others are clear and spiky. You can even have a storm produce multiple kinds of hailstones, and hail with multiple textures and layers. Before we get into what these shapes mean, let's talk about how hail forms.
HAIL FORMATION
Hail first starts as a hail embryo - a surface on which hail can grow. Hail embryos can form in a few ways.
1. A raindrop gets pulled upward by an updraft. The raindrop freezes, creating a hail embryo. These can be clear.
2. A group of ice crystals collide and stick together, and get pulled upward. These are typically cloudy.
3. A water droplet collides with and freezes onto snowflakes, creating graupel, which gets pulled upward. These are also cloudy.
HAIL GROWTH
Once a hail embryo forms, it can grow in two ways: wet and dry growth.
Dry growth happens when water freezes instantly to a hailstone. This happens when the air is very cold and there aren’t many water droplets around. How cold? Generally This traps air bubbles in the ice and makes it cloudy.
Wet growth happens when a hailstone is in warmer, but still below freezing air, with lots of water droplets around. The water freezes slowly. The air bubbles escape, and the ice is clear.
WHAT WET AND DRY GROWTH HAVE TO DO WITH STORM STRENGTH
A weaker thunderstorm will produce mainly small, round, and cloudy hail. This hail has formed through dry growth, which doesn’t require a very high amount of water or a very strong updraft. The inside of most hailstones is cloudy, meaning the beginning stage of hail growth is typically dry. This doesn't mean strong storms don't contain dry growth regions. Instead - it means that at a baseline, a weak storm will almost always contain cloudy and spherical hail. It is easier to produce.
Wet growth - typically - means a stronger and more dangerous storm. Spiky and oddly shaped hail form from wet growth. The spikes and lumps are other smaller hailstones that collided and fused together.
This requires a lot of water, a lot of hail, and violent air motion. It’s the collision and fusing of different hailstones that can make hail grow quickly.
Layered hail, alternating between clear and cloudy, means the hail has gone through the storm multiple times. Hail doesn't just move up and down, it can also move side-to-side in a storm. In fact, this is likely when you see alternating clear and cloudy regions as the stone has moved from regions of wet growth, to dry growth, to wet growth again. Regardless, each time it goes through the updraft, a new layer forms. Stronger storms have stronger updrafts that hold hail up for a longer period of time... meaning the hail will have more layers.
WHAT HAIL CAN TELL YOU ABOUT STORM RISKS
The shape and texture can tell you about other storm risks. For example, tornadoes require a rotating thunderstorm updraft. These storms contain larger hail, which is often lumpy in shape from tumbling through the clouds.
Another type of hail a rotating thunderstorm can produce is flatter in shape - almost like a pancake. This happens when the stone is rotating consistently in a predictable fashion.
Either way -water gets deposited unevenly leading to the pancake or lumpy shape. A rotating storm doesn't always produce a tornado, but hail that looks like this is typically associated with a rotating storm.
HAIL OF DIFFERENT SIZES
A storm that’s dropping hail of different sizes at the same time signals a storm in transition. Sometimes it means a storm is weakening, other times it means one storm is splitting into two storms. A weakening storm will begin dropping hail that was previously held up by the updraft, and the new hailstones that form will be smaller before falling as well.
And a storm that's splitting will typically have more than 1 updraft sustaining hail. As these updrafts begin to split apart, if you're in a certain spot you can get hit by both regions at nearly the same time.
So in essence, the shape of hail can tell you about the storm’s strength, beyond just the size of the stone. Clear layers typically indicate a stronger storm, and lumpy hail can sometimes signal increased tornado potential.
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