Thunderstorm Terms Explained!

What makes a thunderstorm severe? And what's the difference between "scattered" and "isolated" thunderstorms? Find out!

How often has this happened to you? You’re trying to plan some outdoor recreation — perhaps a picnic, or a hike, or a day at the beach — and the forecast calls for “isolated thunderstorms.” You scratch your head, wondering whether or not to cancel your plans.

Weather reports can be tricky to understand if you don’t know the terminology. We’ll break it down for you, so that the next time you see one of these terms, you’ll be weather wise and know what they mean!

Isolated thunderstorms: The National Weather Service uses the term “isolated” to describe a less than 30% chance of measurable precipitation (0.01 inch) for a given location.

Likely thunderstorms: The National Weather Service uses the term “likely” to describe 60% or greater probability of measurable precipitation (0.01 inch) for a given location.

Scattered thunderstorms:
The National Weather Service uses the term “scattered” to describe a 30% to 50% chance of measurable precipitation (0.01 inch) for a given location.

Severe thunderstorm: To be classified as severe by National Weather Service standards, a thunderstorm must meet ONE of the following three criteria: wind speeds reach 58 mph or faster; hail is three quarters of an inch in diameter or larger; or if the thunderstorm produces a tornado or tornadoes. Even if a thunderstorm is not classified as severe, lightning and heavy rain can still pose a danger.

Severe thunderstorm warning: Severe thunderstorms are occurring or will definitely occur in the warning area. A severe thunderstorm has been detected Doppler weather radar or seen by official Skywarn spotters or other designated persons, such as local law enforcement.

Severe thunderstorm watch:
Severe thunderstorms are possible in and around the watch area. A watch does not mean that thunderstorms will definitely occur, just that conditions are favorable for the development of severe thunderstorms.

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Jaime McLeod

Jaime McLeod is a longtime journalist who has written for a wide variety of newspapers, magazines, and websites, including She enjoys the outdoors, growing and eating organic food, and is interested in all aspects of natural wellness.


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Pratap Chandra charan(Ex-Army)

Newsletter thunderstorm will be gone

B. Mooney

Jim W., I think you may have mistakenly heard “Squaw Line” for “SQUALL” Line I’ve never heard of a “Squaw” line up here in Michigan – but I have been found to be wrong once or twice in my life… LOL. Seriously though, it’s a good story but not a very tactical move to sacrifice the women and children out front in a battle. Perhaps someone from the weather business will post a note here to let us know for sure. I’ve looked and can’t find it in a web search either, so who knows?
PS: Keep on learning. I love it too and can’t imagine a day going by without finding something new and interesting… even if it’s only learning that what I knew yesterday was not exactly right. So what…it taught me something!

Jaime McLeod

Yes, B. Mooney, the term is “squall line.”

Margie Artuso

Hi Jaime
Thanks for the article – for some reason I have been drawn to keeping track of the daily weather in my area – I have the weather Icon on my desktop at work and check the weather daily to plan my outdoor activities. Not sure when or why I became so interested in the weather but I have been known to hold off washing my car with the knowlwedge that we have a 50% chance of rain! LOL


The hail criteria for a severe thunderstorm is now 1 inch in diameter or larger, not three quarters of an inch in diameter or larger

Jim Whittington

I enjoy learning,like these weather terms!! I believe,I know some of the other terms,and where they came,but would love to know more.Like,”Squaw line”,from the actions of the indians,when the Calvary,went in to war,the Squaws and children,would come out with sticks and knives,etc This was up front and bad!!

Gardner Berry

I was hoping to hear an explanation of “heat lightning.” To settle an ongoing discussion. I say lightning is lightning, she says heat lightning is a real thing and not a threat.

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