Watches tend to cover large areas that can encompass several states. Locally issued warnings are much smaller and tend to cover specific counties or cities.
Risk categories for storms range from marginal to high risk.(Credit: National Weather Service)
What defines watches and warnings?
A severe thunderstorm watch simply means that conditions are favorable for the development of severe thunderstorms during the next few hours.
A severe thunderstorm warning indicates that severe weather has been either seen on radar or reported by weather spotters or is expected within the hour, according to the Storm Prediction Center. A thunderstorm is considered to be severe if it produces hail that's at least one inch in diameter, has winds 58 miles an hour or stronger or has a tornado. About 10 percent of thunderstorms are classified as severe, but even those that don't meet these criteria can be dangerous.
Most thunderstorms, including those that are severe, develop in the spring and summer, but they can occur any time of year.
In some cases, severe thunderstorms develop when no watch has been issued. Watches primarily cover areas where the threat is expected to last for several hours, but severe thunderstorms can sometimes pop up without a watch being issued first.
What action should you take?
During a thunderstorm watch, stay informed so that you'll be aware if a warning is issued. You can do this listening to a weather radio, checking AJC.com or listening to local weather forecasts on TV.
If a severe thunderstorm warning is issued, continue to listen for more information and be prepared to take action if necessary. Hail, lightning and strong straight-line winds can sometimes develop during a severe thunderstorm. These winds are common, with 16,254 reports from 2002-11, according to The Weather Channel. They can knock down limbs or entire trees and damage homes and other buildings in addition to causing power outages.
Tornadoes can sometimes also develop along with severe thunderstorms, so it may be necessary to take shelter away from windows and get in the center of your home or in your basement if you have one.