Thunderstorms come in many shapes and sizes, ranging in severity and associated dangers. To generate a thunderstorm, the surrounding area needs moisture, unstable air and lift (such as a cold front). Thunderstorms have the capability to produce straight-line winds, large hail, flash floods and even tornadoes. The National Weather Service classifies a thunderstorm as severe if its winds reach or exceed 58 mph, it produces a tornado or if it drops surface hail at least one inch in diameter.
A dry thunderstorm can occur when the rain that is produced does not reach the ground, but evaporates in the air. This is important because lightning will still strike and reach the ground, which can then start structural and wildfires.
Lightning is present in all thunderstorms and results from the buildup and discharge of electrical energy between positively and negatively charged areas. A cloud-to-ground lightning strike begins as an invisible channel of electrically charged air moving from the cloud toward the ground. When one channel nears an object on the ground, a powerful surge of electricity from the ground moves upward to the cloud and produces the visible lightning strike.
Watch Versus Warning
Severe Thunderstorm Watch: Issued when the conditions are favorable for a thunderstorm to develop. A watch will tell you when and where severe thunderstorms are likely to occur.
Severe Thunderstorm Warning: Issued when severe weather has been reported by spotters and indicated by radar. Warnings indicate imminent danger to life and property to those in the path of the storm.