How does hail form? | wtsp.com

TAMPA, Fla. — Hail fell in parts of the Tampa Bay area during severe storms Wednesday night. More thunderstorms are expected on Thursday and Friday, bringing the threat of hail and damaging winds during your evening commute.

Still, temperatures are expected to reach the 90s all week. So, how does ice fall from the sky on a hot Florida day?

It all has to do with the updrafts inside a thunderstorm. 

Hail forms when thunderstorm updrafts carry water droplets high into the atmosphere, where temperatures are below freezing.

The raindrop freezes and grows as it collides with supercooled water — a process known as accretion — causing the hailstone to grow. Once the hailstone is too heavy for the updraft to support, it falls.

As the thunderstorm grows and strengthens, so does the updraft. The stronger updraft will pick up small hailstones and carry them back up, high into the atmosphere.

Supercooled water freezes on the small hailstones, making them grow.

This cycle repeats until the hailstone is too heavy to be carried back up by the updraft. The stronger the storm, the more this process is repeated, and thus, the larger the hailstone.

Stronger thunderstorms will have stronger updrafts. Stronger updrafts can support larger hailstones. For a hailstone to be considered severe, it must be at least an inch in diameter. Some storms are strong enough to support the formation of baseball, softball and even grapefruit-sized hailstones.

Despite Florida being the state with the most thunderstorms, we don’t have as many hailstorms as states like Nebraska, Colorado and Wyoming. That’s because the freezing level of the atmosphere is often too high here to support large hail formation, but it can still happen when strong storms come through. 

NOAA estimates hail size by comparing hailstones to common objects. Here are the agency’s guidelines.

• Pea = 1/4 inch diameter
• Mothball = 1/2 inch diameter
• Penny = 3/4 inch diameter
• Nickel = 7/8 inch
• Quarter = 1 inch — hail quarter size or larger is considered severe
• Ping-Pong Ball = 1 1/2 inch
• Golf Ball = 1 3/4 inches
• Tennis Ball = 2 1/2 inches
• Baseball = 2 3/4 inches
• Teacup = 3 inches
• Softball = 4 inches
• Grapefruit = 4 1/2 inches