warning

A tornado warning (SAME code: TOR) is a public warning that is issued by weather forecasting agencies to an area in the direct path of a tornado or a thunderstorm that is capable of producing a tornado. Modern weather surveillance technology such as Doppler weather radar allow for early detection of rotation in a thunderstorm, and for subsequent warnings to be issued before a tornado actually develops. It is nevertheless still not uncommon that warnings are issued based on reported visual sighting of a tornado, funnel cloud, or wall cloud, typically from weather spotters or the public, but also law enforcement or local emergency management. In particular, a tornado can develop in a gap of radar coverage, of which there are several known in the United States.
A warning should not be confused with a tornado watch, issued in the United States by the Storm Prediction Center (SPC) and in other countries by applicable regional forecasting agencies or national severe weather guidance centers, which only indicates that conditions are favorable for the formation of tornadoes. Although a tornado warning is generally a higher alert level than a tornado watch, in the U.S., it can be surpassed by a higher-level alert—structured as wording that can be added to the official warning product—to warn the public of intense tornadoes affecting a densely populated area.
A tornado watch is not required for a warning to be issued; tornado warnings are occasionally issued when a tornado watch is not active (i.e. when a severe thunderstorm watch is active, or when no watches are in effect), if a severe thunderstorm develops and has a confirmed tornado or strong rotation.

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