A tornado watch is an alert issued by weather forecasting agencies, such as the Storm Prediction Center (SPC) of the National Weather Service (NWS) in the United States, indicating that atmospheric conditions are favorable for tornadoes to develop within a specific region over the next several hours. Unlike a tornado warning, a watch does not mean a tornado has been observed, but rather that the environment is primed for severe thunderstorms capable of producing them. These storms can also bring large hail, damaging straight-line winds, intense lightning, and flash flooding, meaning a tornado watch effectively also serves as a severe thunderstorm watch. When a watch is issued, residents are urged to review safety plans, monitor local media or weather radios, and be prepared to seek shelter in a basement or interior room if a warning is later issued. The SPC issues these watches for the lower 48 states, typically well in advance of the severe weather's arrival to give people time to prepare.