The National Weather Service RADAR network (NEXRAD) is constantly sampling the atmosphere and sensing objects that reflect its transmitted energy. The NEXRADs also measure the doppler shift of the reflected energy to provide an estimate of the reflected particles speed toward or away from the RADAR. Algorithms run on this information and organized storm motions are diagnosed. The featured map shows the location of tornado vortex signatures (TVS) diagnosed from the five RADAR sites covering the state. The TVS reported from the NEXRAD is a indication of a storm capable of producing or is already producing a tornado. Due to physical mechanics of doppler RADAR, these signatures can only be diagnosed at a range close to the RADAR. On the map, you'll notice many areas in Iowa without any reports. The reason is not that they don't have any tornados, but they are too far away from the closest RADAR for the algorithm to work.

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