The Violent Thunderstorms of Spring

Forrest M. Mims III

Residents of much of the United States know more than they care to about giant thunderstorms and the hail and tornadoes they sometimes produce.

It's spring thunderstorm season across the US, and already several communities have been struck by powerful winds, tornadoes and large hail.

Recently a powerful storm scattered baseball-size hail across a popular outlet mall near San Marcos, Texas, and caused major damage to hundreds of cars. The top of that highly concentrated storm reached 21.3 km (70,000 feet)! This was well into into the bottom of the stratosphere.

The tops of thunderstorms may often exceed 15 km (50,000 feet). But a 21 km thunderstorm top is unusual.

The week after the hail storm that struck San Marcos, a similar storm smashed across nearby San Antonio. It’s top reached 19.8 km (65,000 feet).

The air in the tops of these very tall storms is very cold. Updrafts of air within the cloud are very powerful and can exceed 160 km/hour (100 miles/hour).

This is the recipe for hail.

Hail is formed when rain drops are blown high up into the frigid portions of a thunderstorm, where the drops freeze into ice.

The balls of ice become coated with more water and ice as strong updrafts keep them suspended in the cloud. The ice often forms distinctively visible layers as it forms.

Eventually, the weight of the ice balls is too great for the updraft to keep them in the cloud, and they fall to the ground as hail.

Big storms have very powerful updrafts, so hail in these storms has more time to grow in size. This explains why storms like the one that hit San Marcos can produce hails the size of baseballs.

Giant thunderstorms can produce both tornadoes and powerful gusts called straight-line winds. Tornadoes get more publicity because of the damage they cause and because of their rotation and their distinct appearance.

Even relatively small hail can devastate crops and trees. Large hail stones like those that fell on San Marcos can shatter windshields, windows, signs and even roof tiles. Large hail can also seriously injure people.

Until recently, the largest documented hailstone in the US was a monster that fell in Coffeyville, Kansas, in 1970 (Fig. 1). It weighed 0.75 kg (1.67) pounds and was 14.4 cm (5.7 inches) across.

The Coffeyvile record was broken in 2003 when a hailstone measuring 18 cm (7 inches) in diameter fell at Aurora, Nebraska!

Forrest M. Mims III and his science are featured online at www.forrestmims.org and www.sunandsky.org/.

Recently a powerful storm scattered baseball-size hail across a popular outlet mall near San Marcos, Texas, and caused major damage to hundreds of cars. The top of that highly concentrated storm reached 21.3 km (70,000 feet)! This was well into into the bottom of the stratosphere.

The tops of thunderstorms may often exceed 15 km (50,000 feet). But a 21 km thunderstorm top is unusual.

The week after the hail storm that struck San Marcos, a similar storm smashed across nearby San Antonio. It’s top reached 19.8 km (65,000 feet).

The air in the tops of these very tall storms is very cold. Updrafts of air within the cloud are very powerful and can exceed 160 km/hour (100 miles/hour).

This is the recipe for hail.

Hail is formed when rain drops are blown high up into the frigid portions of a thunderstorm, where the drops freeze into ice.

The balls of ice become coated with more water and ice as strong updrafts keep them suspended in the cloud. The ice often forms distinctively visible layers as it forms.

Eventually, the weight of the ice balls is too great for the updraft to keep them in the cloud, and they fall to the ground as hail.

Big storms have very powerful updrafts, so hail in these storms has more time to grow in size. This explains why storms like the one that hit San Marcos can produce hails the size of baseballs.

Giant thunderstorms can produce both tornadoes and powerful gusts called straight-line winds. Tornadoes get more publicity because of the damage they cause and because of their rotation and their distinct appearance.

Even relatively small hail can devastate crops and trees. Large hail stones like those that fell on San Marcos can shatter windshields, windows, signs and even roof tiles. Large hail can also seriously injure people.

Until recently, the largest documented hailstone in the US was a monster that fell in Coffeyville, Kansas, in 1970 (Fig. 1). It weighed 0.75 kg (1.67) pounds and was 14.4 cm (5.7 inches) across.

The Coffeyvile record was broken in 2003 when a hailstone measuring 18 cm (7 inches) in diameter fell at Aurora, Nebraska!

Forrest M. Mims III and his science are featured online at www.forrestmims.org and www.sunandsky.org/.