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The most common weather alert might also be the most misunderstood

Many people are confused about severe thunderstorm warnings, but still take the right actions

An orb of green light extends below the cloud base during a lightning flash on July 19, 2016 in Washington (Kevin Ambrose for The Washington Post)
7 min

Of more than 40 types of watches, warnings and advisories issued by the National Weather Service, one stands out. The severe thunderstorm warning is issued more than any other alert, but it also might be the most misunderstood.

Most people don’t know it, but the presence of frequent lightning or heavy rain has no bearing on whether a thunderstorm is considered severe. The Weather Service only issues a severe thunderstorm warning if it produces winds of at least 58 mph or hail at least one inch in diameter.

How well the public understands severe thunderstorms looms large now that they are starting to ramp up from their winter lull toward a summer peak. Many states conduct severe weather awareness weeks in March to educate people about these storms and their alerts, which are issued more than 80,000 times per year on average in the United States, according to the consumer research firm ValuePenguin.

To better understand what the public knows about severe thunderstorm warnings, researchers at the University of Oklahoma surveyed more than 1,400 U.S. adults about what hazards the Weather Service considers when issuing severe thunderstorm warnings. Eighty percent of respondents correctly identified wind, but only 58 percent correctly identified hail. Perhaps more concerning, 77 percent identified lightning, 76 percent rain and 67 percent flooding, none of which are part of the criteria for a severe thunderstorm warning.

Understanding the storm warning confusion

The confusion around severe thunderstorm warnings “isn’t super surprising,” said University of Oklahoma research scientist Makenzie Krocak during a presentation at the American Meteorological Society annual meeting in January. “When you see [forecasts] talking about severe thunderstorms, what icons do you often see? A lightning bolt, and a raindrop. So it’s not overly surprising that people then associate lightning and water with these warnings.”

To add to the confusion, severe thunderstorm warnings are sometimes issued for showers that are producing strong winds but not lightning or thunder, such as the warning issued Wednesday by the Weather Service office serving the San Francisco and Monterey Bay Area, for winds up to 80 mph.

Despite misconceptions about which hazards factor into severe thunderstorm warnings, Krocak isn’t necessarily suggesting a name change.

“In general, I’d say that we don’t have evidence yet that changing the name of the warning would impact understanding or response,” Krocak said in an email. “There’s also a lot of built-up knowledge with the current name, so we would need to understand if and how changing the name would impact people with that institutional knowledge and their intended response.”

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Chris Wirz, who studies weather risk communication at the University Corporation for Atmospheric Research, notes that the warnings include descriptions of expected impacts and recommended safety precautions.

“So even if people are confused about which hazards are covered, the warning will tell them what to expect and what they can do to stay safe,” Wirz said in an email. “There is also a lot of other communication that is happening before these warnings are ever issued. So by the time warnings are even needed, many people will have an idea of what to expect and how they can respond.”

Misunderstandings aside, about 80 percent of survey respondents said the Weather Service issues “the right amount” of severe thunderstorm warnings, and most said they plan to take actions to protect themselves if they receive a warning.

As for why lightning is not part of the criteria for a severe thunderstorm warning, meteorologist Jim Duncan explained in a story he wrote for The Washington Post last year that it only takes one lightning bolt to kill or injure and that lightning can strike whether or not a storm is deemed severe. That’s why the Weather Service and public safety experts advise “when thunder roars, go indoors,” and stay there until 30 minutes after the last sound of thunder. Over the past 10 years, an average of 23 Americans were killed by lightning annually and hundreds were injured.

Tiers of warning

Since not all severe thunderstorms are created equal, the Weather Service introduced “damage threat” categories for severe thunderstorm warnings starting in 2021, with the goal of better communicating the severity and potential impacts of thunderstorm winds and hail. The three categories are defined as:

  • Base — Thunderstorms expected to only meet the minimum criteria of at least 58 mph winds or hail one inch in diameter (about the same as a quarter). Expected impacts include damage to vehicles, trees, roofs and siding.
  • Considerable — Thunderstorms expected to produce winds of at least 70 mph or hail at least 1.75 inch in diameter (about the same as a golf ball), causing injury to people and animals outdoors. Other expected impacts include damage to roofs, siding, windows, vehicles, trees, mobile homes and outbuildings.
  • Destructive — Thunderstorms expected to produce winds of at least 80 mph or hail at least 2.75 inches in diameter (about the same as a baseball), resulting in life-threatening situations and severely injuring people and animals outdoors. Other expected impacts include power outages, shattered windows, and extensive damage to trees, roofs, siding, vehicles and mobile homes.

Only those severe thunderstorm warnings labeled as “destructive” now trigger emergency weather alerts that are delivered through mobile carriers.

The introduction of the damage threat categories for severe thunderstorms is part of a larger effort by the Weather Service to simplify and clarify its watches, warnings and advisories by reducing the number of alert types and refining the alert language.

For example, the Weather Service is preparing to replace advisories, such as “wind advisory” or “coastal flood advisory,” with what it calls “plain language” headlines that more clearly and quickly convey the threat. The change, scheduled for no earlier than 2025, is based on social science research that indicated public misunderstanding of advisories, which are issued when hazardous weather is happening or imminent, but the expected impacts are less serious than a warning.

What should you do if there’s a severe thunderstorm warning?

Social science research has discovered not only do people not understand the criteria for a severe thunderstorm warning, but they also frequently confuse a storm warning with a storm watch, two very different things.

A severe thunderstorm watch is issued when severe storms are possible but not yet certain. If your area is placed under a watch, experts advise that you stay tuned to trusted sources of weather information and be ready to act if a warning is issued. This is usually a good time to secure outdoor objects that could blow away or cause damage or injury, move light objects inside, and consider postponing outdoor activities.

A severe thunderstorm warning is issued when severe storms are imminent or already happening. If you receive a warning for your area, you should stay inside a sturdy building or shelter and away from windows and doors, bring pets inside, draw blinds and shades over windows, and avoid electrical equipment and plumbing. It’s also a good idea to turn off the air conditioner and unplug appliances, computers and other electronics to avoid damage from a power surge.

The Gulf of Mexico is very warm. That could mean a bad tornado season.

If you can’t make it safely to a sturdy building or shelter, a hard top vehicle (not a convertible) can offer you some protection with the windows closed. (However, automobiles are not safe at all in the case of a tornado.) Avoid open spaces, high ground, water, picnic shelters, dugouts and bleachers, and tall, pointy objects like trees and flagpoles.