Photo from
National Center for Atmospheric Research

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

Credit: NOAA Photo Library, NOAA Central Library

According to NOAA, the Kansas City hail storm on April 10, 2001 was the costliest hail storm in the U.S. which caused damages of an estimated $2 billion.

Even small hail can cause significant damage to young and tender plants

Credit: NOAA Photo Library, NOAA Central Library

• Inside of a thunderstorm are 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 32F...our water droplet freezes.
• As 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!
  
  

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Fortunately...most hail is small - usually less than 2 inches in diameter.

The largest hailstone fell on June 23, 2003 in Aurora, Nebraska and had a diameter of  7.0 inches, a circumference of 18.75 inches, and weighed just under 1 lb. The heaviest hailstone fell in Coffeeville, Kansas on September3, 1970 and weighed 1.67 lbs.  It had a diameter of 5.7 inches and a circumference of 17.5 inches.

Credit: NOAA Photo Library, NOAA Central Library

Hailstones can begin to melt and then re-freeze together - forming large and very irregularly shaped hail

Is there a way to estimate hail size...or do I have to go outside and measure it?

• It's often difficult to get an accurate measurement of hail diameter - especially when it's falling
• The table to the right helps observers estimate the size of hail based on average diameters of common items
• When in doubt - play it safe and wait until the thunderstorm has moved away before going outside to measure the size of hail

Estimating Hail Size

• Pea  = 1/4 inch diameter

• Marble/mothball = 1/2 inch diameter

• Dime/Penny = 3/4 inch diameter - hail penny size or larger is considered severe

• Nickel = 7/8 inch

• Quarter = 1 inch

• Ping-Pong Ball = 1 1/2 inch

• Golf Ball = 1 3/4 inches

• Tennis Ball = 2 1/2 inches

• Baseball = 2 3/4 inches

• Tea cup = 3 inches

• Grapefruit = 4 inches

• Softball = 4 1/2 inches

Often large hail is observed immediately north of a tornado track - but the presence of hail doesn't always mean a tornado and the absence of hail doesn't always mean there isn't a risk of tornadoes.

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• There is no positive way to look at a thunderstorm in the distance and tell if it will produce hail reaching the ground.
• Meteorologists use weather radar to "look" inside a thunderstorm. Since hail reflects more energy back to the radar than raindrops it often shows up in red shades.
• The WSR-88D Doppler Radar can also estimate size of the hail based on the amount of energy reflected back.

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Damaging Wind
Gusts
58 miles per hour (50 knots) or higher

Or

Large Hail
3/4 inch in diameter
(penny size) or larger

Or

Tornadoes

A SEVERE THUNDERSTORM WARNING means a severe thunderstorms 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.

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Severe 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.