Thunderstorm forecasting is very similar to the forecasting used to predict tornadoes. Four times daily, a severe weather outlook is issued on a nationwide basis indicating whether conditions are either favorable or unfavorable for thunderstorms to develop in specific regions of the United States.
To forecast thunderstorms, meteorologists use a variety of data. Surface and upper air observations are studied to find areas of low level moisture and instability, and to determine how winds aloft might influence storm development.
Satellite imagery is used to help track the movement of weather systems that might generate thunderstorms. Forecasters scan computer model data to help determine where favorable areas for thunderstorm formation might be located further out in time. Radar and satellites are used to track the storms once they do form.
Most thunderstorms pose the threat of heavy downpours. gusty winds, and cloud-to-ground lightning. Sometimes, however, atmospheric conditions become favorable for particularly dangerous thunderstorms to form. These severe thunderstorms are defined as producing one or more of the following: hail 3/4 of an inch in diameter or greater, wind gusts to 58 mph or more, or a tornado.
Meteorologists at the Storm Prediction Center in Norman, Oklahoma, are tasked with monitoring the atmosphere for signs of severe thunderstorms and tornado development. They will issue a Severe Thunderstorm Watch for areas where conditions are favorable for the formation of severe storms.
Once a severe thunderstorm has actually been sighted or observed on radar, a Severe Thunderstorm Warning will be issued by the local office of the National Weather Service.