Hail

A city street covered with hailImagine a baseball dropped from an airplane flying at 30,000 feet. Imagine that baseball reaching speeds of 120 MPH as it falls to the ground. And, imagine you’re under it!

Imagine you’re driving along at 70 miles per hour. Or your crops are under the hail producing thunderstorm. Or your home is under the thunderstorm.

Hail causes $1 billion in damage to crops and property each year

The costliest hailstorm in the United States was in Denver in July 1990 with damage of $625 million. Even small hail can cause significant damage to young and tender plants

How Hail Forms

Thunderstorms contain strong updrafts of warm air and downdrafts of cold air. If a water droplet is picked up by the updrafts, it can be carried well above the freezing level. With temperatures below 32 degrees Fahrenheit, our water droplet freezes.

A graphical representation of the lifecycle of a hail stoneAs the frozen droplet begins to fall...carried by cold downdrafts...it may thaw as it moves into warmer air toward the bottom of the thunderstorm

But, our little half-frozen droplet may also get picked up again by another updraft...carrying it back into very cold air and re-freezing it. With each trip above and below the freezing level, our frozen droplet adds another layer of ice.

Finally...our frozen water droplet...with many layers of ice - much like the rings in a tree...falls to the ground - as hail!


Size of Hail

Observers use the following measurements to estimate the size of hail based on average diameters of common items:

Estimated SizeAverage Diameter
Pea1/4 inch
Marble/mothball1/2 inch
Dime/penny3/4 inch
Nickel7/8 inch
Quarter1 inch
Ping-pong ball1 1/2 inches
Golf ball1 3/4 inches
Tennis ball2 1/2 inches
Baseball2 3/4 inches
Teacup3 inches
Grapefruit4 inches
Softball4 1/2 inches

Radar imageSevere Thunderstorm Determinations

The National Weather Service considers a thunderstorm severe only if it produces

  • Damaging Wind Gusts 58 miles per hour (50 knots) or higher,
  • Large Hail 3/4 inch in diameter (penny size) or larger, or

Tornadoes

  • A Severe Thunderstorm Watch means conditions are favorable for thunderstorms to become severe...or severe thunderstorms to move into the watch area. Watches are intended to heighten public awareness of the possible severe weather threat. Keep an eye on the sky. Stay tuned to NOAA Weather Radio or local radio, television, or cable to know when severe weather warnings are issued for your area.
  • A Severe Thunderstorm Warning means a severe thunderstorm poses an imminent danger to life and property to those in the path of the storm. When severe weather is indicated by weather radar or is reported by trained SKYWARN Severe Weather Spotters or law enforcement officials a warning is issued immediately.  

A graphical representation of hail forming in a storm cloudSevere Thunderstorm warnings are sent to local radio and television stations and are broadcast over your local NOAA Weather Radio serving the warning area.

These warnings are also relayed to local emergency management and public safety officials who can activate local warning systems to alert communities to the danger.