Severe Weather: Learn About Storm-Spotting


Storm-spotters are volunteers who are trained to identify and observe hazardous weather conditions. Once they are trained, storm-spotters watch the skies when storms move into an area and provide reports to local weather stations. Many weather stations rely on a storm-spotting network of volunteers to get timely and accurate updates on severe storms.

Thunderstorms and Tornadoes

Thunderstorms develop when there’s a lot of moisture in the air and an updraft causes warm air to clash with cooler air. Thunderstorms can be dangerous. Some last only a few minutes, and others continue for several hours. The mature stage of a thunderstorm will include heavy rain and possibly hail. A severe thunderstorm often lasts longer as warm and moist air continues to fuel the storm. Longer thunderstorms might also be classified as supercell thunderstorms, and these organized storms can bring high winds, large hail, and tornadoes with them. These weather conditions often produce significant roof damage.

  • When upward and downward winds happen at the same time, a thunderstorm is the most dangerous because it can cause tornadoes, high winds, hail, and flooding.
  • A severe thunderstorm can produce hail that is at least an inch in diameter, wind gusts of 58 miles per hour or more, wind or hail damage, or a tornado.
  • A supercell thunderstorm has a persistent rotating updraft. They’re not as common, but these storms can cause a lot more damage.
  • A tornado is a rotating column of air that moves violently. Tornadoes form during thunderstorms, and they occur when winds blow in different directions and increase with height.
  • Tornadoes are measured based on wind speed and classified using the Enhanced Fujita Scale. An EF-0 tornado has wind speeds between 65 and 85 miles per hour. An EF-1 tornado has wind speeds between 86 and 110 miles per hour. Winds between 111 and 135 fall into the EF-2 classification, and wind speeds between 136 and 165 miles per hour designate an EF-3 tornado. EF-4 tornadoes have wind speeds between 166 and 200 miles per hour, and winds exceeding 200 miles per hour indicate an EF-5 tornado.

What Storm-Spotters Observe

Storm-spotters observe weather conditions and report to the National Weather Service and local public safety officials. Spotters are trained to understand what different types of storms look like and how to identify areas where severe storms may develop. Storm-spotters learn to recognize signs that often come before tornadoes and how to tell the difference between actual tornadoes and similar storms. Data provided by storm-spotters helps forecasters provide better warnings to help people take cover and stay safe.

  • Storm-spotters look for violently rotating columns of air, which indicate a tornado. A funnel doesn’t need to touch the ground to be a tornado. Tornadoes can have different shapes, with some being wider and others being thinner, and they can even look different colors depending on what’s inside them and the sunlight around them.
  • Storm-spotters might see a funnel extending from the bottom of a cloud. A funnel cloud by itself is not a threat, but it could be an indication that a tornado is coming.
  • Observers might notice a wall cloud, which is a persistent lowering from the base of a thunderstorm. Not all wall clouds will produce tornadoes, but they often accompany a supercell thunderstorm. Wall clouds may rotate, and if they do, they often lead to a tornado. Storm-spotters should watch wall clouds carefully to see what develops.
  • Storm-spotters might notice a cloud base that doesn’t produce precipitation. A rain-free base usually shows where a thunderstorm updraft is occurring. Tornadoes could develop from wall clouds that attach to a rain-free base. But sometimes, a rain-free base looks dry but actually has large raindrops or hail.
  • Storm-spotters also watch for supercell thunderstorms. These storms often bring strong straight-line winds, hail, and tornadoes.
  • A strong downdraft from a storm can create winds that are as damaging as a tornado. Storm-spotters understand that these winds can come with thunderstorms as well as weaker showers.

Additional Severe Weather Resources

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