Severe Summer Storms

Summer storm clouds and lightning over Cornell University Campus


All thunderstorms are dangerous despite the fact that they are generally localized in a small geographical region. It is important to note that every thunderstorm produces lightning, which is responsible for more deaths annually than hurricanes or tornadoes.

The National Weather Service classifies a thunderstorm as severe if it has wind gusts greater than 58 mph, hail that is 3/4 inch in diameter or produces a tornado. Severe thunderstorms can lead to flash flooding, straight-line winds of 100 to 150 mph, damaging hail, and tornadoes.  A typical thunderstorm is 15 miles in diameter and lasts for 20-30 minutes. On average, 100,000 thunderstorms occur in the United States each year with 10% (10,000) classified as severe.

Maps and Alerts 

NOAA Weather Radios – National Weather Service: “all-hazards” emergency alert messages and recommended equipment for all homes and businesses

Severe storm watch means that severe storms are possible and it is important to pay attention to weather reports and be ready to find shelter if a warning is issued.

Severe storm warning indicates that severe weather has been reported by spotters and there is imminent danger to life and property.  Take cover immediately.

Storm Prediction Center– National Oceanic and Atmospheric Administration, National Weather Service: regularly updated maps illustrating severe storm probabilities in the U.S.

Recommended Resources 

About Thunderstorms – American Red Cross: what to do before, during and after a thunderstorm

Disaster Assistance Programs – Farm Service Agency, United States Department of Agriculture

Severe Weather Preparedness Guide for Schools – National Oceanic and Atmospheric Administration, National Weather Service

Thunderstorm, Tornadoes, Lightning Preparedness Guide (PDF) – U.S. Department of Commerce:  explains thunderstorms and related hazards and suggests life-saving actions you can take

Lightning safety

Lightning is a major threat during a thunderstorm because it is very unpredictable and it can strike as far as 10 miles away from the actual rainfall area. An average of 62 people are killed from lightning strikes each year with the majority of deaths occurring to people who did not seek shelter inside during the storm. Many more injuries occur and some may result in long-term, debilitating symptoms such as memory loss, sleep disorders, attention deficits, irritability, depression, and muscle spasms.

Do you know the 30/30 rule for lightning safety?

First 30: if there are 30 seconds or less between the lightning flash and hearing thunder, then the lightning is close enough to strike you — go inside immediately.

Second 30: wait 30 minutes after the last lightning flash before leaving your inside shelter area.

Recommended Resources

All of the following resources are from the National Oceanic and Atmospheric Administration and National Weather Service.