Tornadoes have a unique radar signature. It is called hook echo and has been known about since April 1953 when the ISWS (Illinois State Water Survey) found the distinctive difference between a regular storm and a tornado. Using radar to detect tornado activity allows the National weather service to give advance warning of an approaching tornado. The best type of radar to observe the hook echo is a Doppler radar. A tornado becomes visible to the eye when a funnel cloud develops. A funnel cloud is a condensation funnel made of water vapor, which forms in places of extremely low pressures. Another way of spotting a tornado is when it sucks in dust, dirt and debris upward from the ground.