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How far in advance can forecasters identify conditions favorable for tornadoes?

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Weather forecasting Doppler radars, such as this one operated by the U.S. National Weather Service at New Underwood, South Dakota, extract the Doppler frequency shift of the echo produced by a moving target by noting how much the frequency of the received signal differs from the frequency of the signal that was transmitted.

Meteorologists identify conditions favorable for tornadoes through a two-step process that prioritizes public safety and the protection of human life.1

Tornado Watch: By monitoring atmospheric instability, wind profiles, and the movement of the jet stream, forecasters can typically identify regions where conditions are favorable for tornado development one to seven hours in advance. This information is issued as a watch, which alerts the public that severe weather is possible but does not pinpoint specific locations.21
Tornado Warning: Once a storm develops, local offices of the National Weather Service use Doppler radar to monitor for rotation within a mesocyclone or the presence of a tornado vortex signature. A warning is issued when a tornado is spotted visually or detected via radar, indicating that danger is imminent and immediate action is required.21

These modern surveillance systems allow scientists to detect the rotation of supercell thunderstorms long before a funnel cloud is visible, significantly increasing warning times while reducing false alarms.23