Doppler radar, able to sense the winds in the vicinity of a tornado, is another valuable tool. The outward appearance of tornadoes can vary tremendously, even for the same storm viewed at different times or from different angles. A complete funnel need not be visible from cloud to ground for a tornado to be capable of damage. Large tornadoes may resemble a cloud on the ground rather than a narrow funnel. Especially in the eastern United States, rain may wrap around a tornado's circulation and cut off visibility.
Researchers collect many kinds of information on tornadoes by going into the field.
Wall clouds and other visual precursors of tornadoes discovered by chasers are now used by law enforcement and civil defense agencies to issue warnings. The most damaging twisters are often spotted well before they strike populated areas, enabling residents to take cover. The homes of some 20,000 people lay in the path of the 1979 Wichita Falls, Texas tornado, but extensive warnings kept the death toll to a relatively low 42. Although understanding the formation of tornadoes will not lead to their prevention, better information will save lives and property. Research data can be applied to building codes and zoning for areas prone to tornadic storms.