Tornado Detection Depends on Both Trained Spotters and Modern Technology

While tornadoes are possible within any type of thunderstorm, strong or violent tornadoes which cause the most death and destruction almost always develop within mesocyclones or supercell thunderstorms. Supercells are rotating long-lived thunderstorms with intense updrafts which may attain vertical velocities in excess of 70 mph. Visually they can be identified by such features as a rotating wall cloud, which is associated with the strong updraft, and a clear slot which is the result of a rain-cooled outflow or downdraft. When the sinking air within the downdraft begins to wrap around the warmer updraft, strong or violent tornadoes sometimes form.

The National Weather Service Doppler radars can measure air moving both toward and away from the radar. This allows early detection of thunderstorm rotation which usually precedes tornadogenesis. In the figure above left, winds moving away from the radar are green while those moving toward it are red. The close proximity of strong winds moving both toward and away from the radar indicates strong storm rotation and the presence of a violent tornado ( above right ).

As a supercell thunderstorm rotates, it wraps heavy rain and hail around the updraft in a counterclockwise or cyclonic direction. This aspect of the storm produces a HOOK ECHO ( right) on the radar reflectivity image. Often, the presence of a hook echo indicates a thunderstorm may produce a tornado within 10 minutes.  Although strong and violent tornadoes are rare across southwestern New Mexico and far western Texas, meteorological conditions occasionally come together over the region which create the potential for stronger tornadoes. Persons traveling should also remember the risk of strong and violent tornadoes increases significantly as one ventures east of the Rockies. 5                                                                next page