Have you noticed in summertime thunderstorms that we can get different sizes of hail? We actually use the size of hail to help determine how strong (or even severe) a thunderstorm is! Today we will learn how hail stones form and grow to be different sizes.

WHAT YOU NEED: 

• Hair dryer
• Normal size ping-pong ball
• Larger ping-pong ball (here's the link to Amazon listing)

WHAT YOU DO: 

Start with the smaller ping-pong ball. Turn the hair dryer on high and point it straight up in the air. *Use the cool setting if you have it* Place the ping pong ball above the hair dryer in the stream of air. Watch what happens! Turn the hair dryer to the low setting and watch what happens. 

Now do that again but use the larger ping-pong ball and notice what happens differently. 

WHAT IS HAPPENING:

Hail does not form the same way other frozen types of precipitation do, like snow or sleet. Hail stones form in a cloud when tiny bits of ice stick to each other and grow to a larger and larger piece of ice. As that ice gets bigger, it also gets heavier which makes it harder to stay “floating” in the air. A storm needs a stronger updraft (stream of air moving up inside a storm) to allow larger hail stones to grow. If the storm has a weaker updraft (like the low setting on your hair dryer), it will only allow small hail stones to grow in the cloud before they become too heavy to support and fall out of the sky. If the updraft is stronger, like in a well-developed severe thunderstorm, it can support larger hail stones. That allows the hail to grow bigger before it’s too heavy for the updraft to hold aloft and it falls to the ground. 

DISCUSSION IDEAS:

How heavy to you think hail has to be for it to fall out of a cloud? 

How strong do you think the updraft needs to be for it to keep hail up inside the cloud?