TVS

The abbreviation TVS stands for Tornado Vortex Signature. One of three terms will be used to describe the tornadic potential of a certain cell in this column.

• NONE - The potential for a tornado is not existent according to the radar when NONE is shown. That does not necessarily mean that a tornado is not present, given tornadoes can sometimes form starting at the ground, and make their way up. Always heed National Weather Service warnings first.
• ETVS - "Elevated Tornado Vortex Signature" – Circulation does not extend all the way to the lowest tilt on radar with an ETVS, but is strong among the other tilts. An ETVS should be monitored closely for development into a TVS.
• TVS - If a TVS is identified by radar, a tornado is a good possibility, because circulation has been detected through the lowest possible tilt. However, since the radar beam does not pan all the way down to the surface, there is no way to guarantee this. Listen to local media to find out more information or see if storm spotters have confirmed the feature.

Remember that a radar cannot scan the ground to look for a tornadic rotation, which can lead to detection errors. The radar only obtains data from the storm tower, and relies heavily on this to detect a tornado vortex signature.

Since the algorithm which detects the tornadic, or tornado, vortex signature is sensitive, false signatures can at times be detected along frontal boundaries and squall lines, or where a definite wind shift is present, especially when the front edge of a squall line is parallel to the radar beam. A TVS or ETVS does not guarantee a tornado.

When a TVS or ETVS is detected, the radar has found an area of intense and concentrated rotation, more so than a mesocyclone. Watch this for persistence. Other algorithm criteria, such as the strength and vertical depth, must also be met for a radar to indicate a tornado vortex signature.

A TVS or ETVS itself is not a visually observable feature. The possible tornado that could accompany such a signature obviously is visible however.

A radar cannot detect a tornado vortex signature well, or possibly at all, if a thunderstorm is close to the radar site. Beams are unable to extend into the updraft at such a degree from the radar's transmitter. A lesser, or possibly absent, tornado vortex signature is displayed as a result.

Do not question warnings issued by the expert National Weather Service meteorologists. If you feel your life is threatened by a thunderstorm, do not postpone seeking shelter, even if a warning is not in effect for your area.