Lightning is formed by an imbalance of electrical charges in a cumulonimbus cloud. These large clouds have strong vertical and downdraft winds. As the water particles and ice crystals are violently bounced around within the cloud the positive and negative charges begin to congregate at the bottom and top of the cloud. Positive charges build up on the ground and negative charges build up at the base of the cloud. The negative charges begin to move downward in a zigzag stroke called a stepped leader (they cannot be seen at this point). Positive charges build up on the ground, congregate around the highest point (a tree, lightning rod, or even a person). Since positive and negative charges attract, the positively charged upward streamer begins to reach up toward the negatively charged, downward stepped leader. When the two strokes meet a bright bolt of lightning, called the return stroke, is visible. At 54,000 degrees Fahrenheit, a lightning bolt is 5 times hotter than the surface of the sun! The sudden, rapid expansion of air is heard as a clap of thunder. There can be no thunder without lightning. The sound of thunder travels at 5 miles per second, so it is possible to calculate the distance of lightning by counting how many seconds it takes to hear the thunder after seeing a bolt of lightning.
Lightning rods are used to channel the electricity down to the ground if a building is hit. People can often feel the hair stand up on their arms, their head or the back of their neck before a lightning strike (note the little stick man!). Never stand under a tree during a thunderstorm, if it is struck by lightning it could be fatal. A car or a building is the safest place to be.