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What is a severe thunderstorm?

Thunderstorms are the most common type of hazardous weather around the globe. All thunderstorms are dangerous as by definition, they include lightning. However, the most intense and dangerous thunderstorms are those classified as severe. To be labeled as a severe thunderstorm, it must contain one or more of the following:

  • Hail at least an inch in diameter
  • Winds in excess of 58 miles per hour
  • A tornado

Ready...Most hazardous weather is forecast days in advance. Begin your preparations by paying attention to the weather forecast. The Key Impacts Graphic is a great product by the National Weather Service that highlights the potential for hazardous weather over the next seven days.

Storm Prediction Center's Thunderstorm Risk Categories


Understand your risk of severe weather! When severe weather is expected, the Storm Prediction Center will issue convective outlooks out to 8 days that highlight the risk for severe weather.

Set...If severe weather is possible, then a Severe Thunderstorm Watch will be issued. This does not mean that severe thunderstorms will occur, only that they are possible. This means that conditions are favorable for severe thunderstorms, and you need to pay attention and stay aware in case a severe thunderstorm does develop. Listen to your NOAA weather radio or tune in to your local broadcast media for the latest information. Have a plan in place that includes where you will go in case a warning is issued.

Go! When a severe thunderstorm is occurring or is imminent, the National Weather Service will issue a Severe Thunderstorm Warning. This means that you need to implement your plans to protect yourself.

Severe Thunderstorm Watch Severe Thunderstorm Warning
When severe thunderstorms are possible, a Severe Thunderstorm Watch will be issued. Severe Thunderstorm Watches are issued for multiple counties and are in effect for several hours. This is your notification that you need to stay aware and be prepared to take action should a warning be issued. When a severe thunderstorm is occurring or is imminent, a Severe Thunderstorm Warning will be issued. A Severe Thunderstorm Warning is a storm-based warning in the form of a geographic polygon, and it is typically in effect for 30 to 45 minutes. This is your notification that you need to act and seek shelter.



Lightning strike destroys a tree in Los Alamos






Did you know that most people who are struck by lightning are not struck during the height of the thunderstorm but before or after its greatest intensity? This is because they are often caught unprepared as lightning can strike well away from a thunderstorm! Lightning is erratic and unpredictable, and nobody is safe outside during a thunderstorm. The best place you can be during a thunderstorm is inside a sturdy building. Stay away from windows and avoid using plumbing and electrical devices. If you have time, secure any loose, lightweight outdoor objects as they could become dangerous missiles in the event of strong winds. Remember to bring your pets inside. Do not go back outside until at least 30 minutes after the last lightning strike or rumble of thunder.


If you are caught outside during a thunderstorm, take shelter in a nearby sturdy building or in your automobile. Do not touch anything metal in your car. No place outside is safe during a thunderstorm. If you are caught outside, keep moving towards a shelter.

No place outside is safe during a thunderstorm as seen by this tree in Los Alamos that was destroyed by a lightning strike on August 19, 2016. Photo by Jon Doorn.  


When Thunder Roars, Go Indoors See a Flash, Dash Inside


If you are close enough to hear thunder, you are close enough to be struck by lightning!