Adapted from "Watch or Warning, What's the Difference?" James West, WeatherBug Meteorologist and "What is the difference between a watch and a warning?", National Weather Service)

The spring and summer months often bring the risk of tornadoes and severe thunderstorms that can generate damaging winds, dangerous lightning and large hail.

The National Weather Service, to help prepare and warn people of changing weather conditions, will often issue severe weather watches and warnings for areas that could be affected by severe thunderstorms and tornadoes.

Below are the definitions for severe thunderstorms and for each type of severe weather watch and warning.

• Severe Thunderstorms: Severe thunderstorms have winds of 58 mph or higher and/or Hail 3 /4 of an inch in diameter or larger
• Severe Thunderstorm Watch: Issued when conditions are favorable for severe thunderstorms to form in and near the watch area during a 3 to 6 hours period.
• Severe Thunderstorm Warning: Issued when severe thunderstorms are occurring or imminent in the warning area. Information in this warning includes: where the storm is, what towns/cities will be affected, and the primary threat associated with the storm.
• Tornado Watch: Issued when conditions are favorable for severe thunderstorms and multiple tornadoes to form in and near the watch area during a 3 to 6 hour period.
• Tornado Warning: A tornado has actually been sighted by spotters or indicated on radar and is occurring or imminent in the warning area. The warning will include where the tornado is and what towns/cities will be in its path.
• Flash Flood Watch:  Indicates that flash flooding is possible in and close to the watch area. Those in the affected area are urged to be ready to take quick action if a flash flood warning is issued or flooding is observed.
• Flash Flood Warning:  Signifies a dangerous situation where rapid flooding of small rivers, streams, creaks, or urban areas are imminent or already occurring. Very heavy rain that falls in a short time period can lead to flash flooding, depending on local terrain, ground cover, degree of urbanization, degree of man-made changes to river banks, and initial ground or river conditions.
• Severe Weather Statement:  Issued when the forecaster wants to follow up a warning with important information on the progress of severe weather elements.

For additional weather information for in the Washington, DC metro area, click on the following link to the Washington Post's Capital Weather Gang: http://blog.washingtonpost.com/capitalweathergang/2008/01/frequent_questions.html#watch_warning_advisory