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Severe Thunderstorm Facts

The National Weather Service considers a thunderstorm severe if it produces hail at least 3/4-inch in diameter, winds of 58 miles per hour or er, or a tornado. Of the estimated 100,000 thunderstorms that occur each year in the United States, about 10 percent are classified as severe.

Every Thunderstorm Needs:

• Moisture to form clouds and rain
• Unstable warm air that can rise rapidly.
• Cold or warm fronts, plus the sun's heat, lift the air to help form thunderstorms

Developing Stage

• Usually little if any rain during this stage.
• Towering cumulus cloud indicates rising air.
• Lasts about 10 minutes.
• Occasional lightning.

Mature Stage
• Most likely time for hail, heavy rain, frequent lightning, strong winds, and tornadoes.
• Storm occasionally has a black or dark green appearance.
• Lasts an average of 10 to 20 minutes but may last much longer in some storms.

Dissipating Stage
• Rainfall decreases in intensity.
• Can still produce a burst of strong winds.
• Lightning remains a danger

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