An Introduction to Hail Basics

Hail is a form of precipitation consisting of solid ice that forms inside thunderstorm updrafts. It can damage aircraft, homes, cars, and can be deadly to livestock and people. (nssl.noaa.gov)

How Does Hail Form?

Hailstones are formed when raindrops are carried upward by thunderstorm updrafts into extremely cold areas of the atmosphere and freeze. Hailstones then grow by colliding with liquid water drops that freeze onto the hailstone’s surface. The hail falls when the thunderstorm's updraft can no longer support the weight of the hailstone, which can occur if the stone becomes large enough or the updraft weakens. (nssl.noaa.gov)

What Are the Sizes of Hailstones?

Hailstones can vary greatly in size, from small pellets to large, damaging stones. The largest hailstone recovered in the United States fell in Vivian, South Dakota, on June 23, 2010, with a diameter of 8 inches and a circumference of 18.62 inches. It weighed 1 lb 15 oz. (nssl.noaa.gov)

Where Do Hailstorms Occur?

Although Florida has the most thunderstorms, Nebraska, Colorado, and Wyoming usually have the most hailstorms. The area where these three states meet – “hail alley” – averages seven to nine hail days per year. (nssl.noaa.gov)

How Fast Does Hail Fall?

The fall speed of hail primarily depends on the size of the hailstone, the friction between the hailstone and surrounding air, the local wind conditions (both horizontal and vertical), and the degree of melting of the hailstone. For small hailstones (<1-inch in diameter), the expected fall speed is between 9 and 25 mph. For hailstones that one would typically see in a severe thunderstorm (1-inch to 1.75-inch in diameter), the expected fall speed is between 25 and 40 mph. In the strongest supercells that produce some of the largest hail one might expect to see (2-inches to 4-inches in diameter), the expected fall speed is between 44 and 72 mph. However, there is much uncertainty in these estimates due to variability in the hailstone’s shape, degree of melting, fall orientation, and the environmental conditions. (nssl.noaa.gov)

How to Protect Yourself and Your Property

• Seek Shelter: During a hailstorm, move to a sturdy building or vehicle. Avoid windows and doors.

• Protect Vehicles: If possible, move vehicles to a garage or covered area. If not, cover them with blankets or tarps to minimize damage.

• Secure Outdoor Items: Bring in or secure outdoor furniture, decorations, and other items that could be damaged or become hazardous during a hailstorm.

• Stay Informed: Monitor local weather reports and heed any warnings or advisories issued by local authorities.

Understanding hail formation and taking appropriate precautions can help minimize the risks associated with hailstorms.