Used to record the pressure drop inside a tornado, this "turtle probe” was one of many created by American storm chaser Tim Samaras. In addition to conducting field research on tornados and starring on the Discovery Channel show Storm Chasers, Samaras designed this type of probe in 1999. The probe’s low, flat, design helped it stay on the ground in the midst of high-speed winds. On June 24, 2003 Samaras used this particular probe to record the pressure drop of the Manchester Tornado, a tornado that struck the unincorporated community of Manchester, South Dakota. The tornado was rated F4, the second most intense rating on the Fujita scale. Although several other probes were placed in the path of the tornado, this probe was the only one to record a direct strike, managing to survive wind speeds of up to 260 miles per hour. When the tornado passed over the probe, because of the extreme pressure gradient between the tornado’s high-pressure exterior and the low-pressure interior, the probe logged a pressure drop of 100 millibars over five seconds, the deepest and fastest pressure drop ever directly recorded in a weather event.

Tornados form in a special kind of rotating thunderstorm known as a supercell, which occurs when wind speed and direction varies at different altitudes. This condition is known as wind shear, and when sufficient, it can cause horizontally rotating tubes of air to form. Because warm air in a thunderstorm rises, it can rotate the horizontal tube of air vertically, turning the whole storm into a supercell. Some supercells form a funnel cloud, which can extend to the ground, becoming a tornado. As the tornado continues rotating, typically counterclockwise, a huge pressure gradient builds up between the tornado’s surrounding air pressure and its center, which is typically 10-20 percent lower. This gradient force generates high wind speeds as air rushes into the lower-pressure center, where it cools and expands, creating the condensation that characterizes a tornado funnel. Meteorologists monitor ground and satellite readings of wind, temperature, and moisture to track and predict the United States’ average 1,000 yearly tornadoes.