By definition every thunderstorm contains lightning. So although every thunderstorm may not be severe (58 mph winds or 1” diameter hail) every thunderstorm is dangerous.
Light travels faster than sound. So you will see the flash of lightning first, then hear the rumble of thunder. I should say you may hear thunder. More on that in a bit. On average, the sound of thunder travels one mile every 5 seconds. If you or someone you know is afraid of storms, there is a simple way to figure out if the storm is moving closer to you or farther away. Count the seconds from the flash of lightning until you hear thunder. Divide that number by 5 and you will have the number of miles you are from the lightning strike. For example if you counted to 10, divide that by 5 and you get 2 miles.
Now back to the statement you may hear thunder. Have you heard of heat lightning? That’s a lightning flash from a thunderstorm so far away you don’t hear the thunder. Typically, the sound of thunder can’t be heard beyond ten miles. On a warm summer night, you may see a flash of lightning from a thunderstorm that is 50 miles away or more.