WSAV NOW Weather: How hail forms

WSAV NOW Weather

SAVANNAH, Ga. (WSAV) — Hail is a type of frozen precipitation that form in strong thunderstorms as solid pieces of ice. Often times when severe storms develop, large hail formation is a threat. Hail stones greater than an inch in diameter can cause harm to you, property, and crops.

To get an idea on how hail forms, let’s first take a look at the basics of thunderstorm development. Thunderstorms form with convection, which is rising air. As clouds for from the cooling and condensing of water vapor, eventually the clouds are able to organize into storms.

Rising warm air acts a fuel to keep the storm going like an engine. The more warm air there is, the stronger and taller storms are able to become. This rising air in the storm is called an updraft.

While storms are developing and growing, the updraft of air is very strong and can reach heights in excess of 30 or 40 thousand feet tall. At those heights, air temperatures are well below freezing which allows ice to form. Temperatures can be as cold as -40°F or below.

Diagram depicting hail formation with an updraft and downdraft within a thunderstorm

In a healthy and mature thunderstorm, as is a rising updraft there is also a downdraft which allows raindrops to fall to the ground.

Within the storm there is a circulation between the updraft and downdraft. This catches some of the falling raindrops to go back up into the storm, refreezing and collecting more ice forming hail.

As the storm’s updraft remains strong, pieces of hail can circulate though the storm many times. The more times it circulates, the larger it can become. Circulation happens until the updraft weakens or the hail becomes too large and heavy to continue rising back into the storm.

Most hail producing thunderstorms in the United States occur in Nebraska, Colorado, and Wyoming. The largest hail stone in the US fell near Vivian, S.D. in 2010. It measured with a diameter of 8” and a circumference of 18.62” and weighed nearly two pounds.

The Coastal Empire and Lowcountry typically does not usually get extremely large hail, but we can get hail large enough that can cause damage.

On Monday, February 15, 2020 some marginally severe storms were able to produce large hail for portions of Bryan and Chatham Counties.

Many WSAV viewers sent us images of large hail that actually helped the National Weather Service to determine that the line of storms moving though was indeed severe. Hail greater than one inch in diameter is a determining factor for a storm being severe or not.

You can email storm pictures anytime to Storm Team 3 to To stay ahead of severe weather, download the WSAV Storm Team 3 weather app for Apple and Android devices.

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