A tornado is a violently rotating column of air that is in contact with both the surface of the Earth and a cumulonimbus cloud or, in rare cases, the base of a cumulus cloud. It is often referred to as a twister, whirlwind or cyclone, although the word cyclone is used in meteorology to name a weather system with a low-pressure area in the center around which, from an observer looking down toward the surface of the Earth, winds blow counterclockwise in the Northern Hemisphere and clockwise in the Southern. Tornadoes come in many shapes and sizes, and they are often visible in the form of a condensation funnel originating from the base of a cumulonimbus cloud, with a cloud of rotating debris and dust beneath it. Most tornadoes have wind speeds less than 180 kilometers per hour, are about 80 meters across, and travel several kilometers before dissipating. The most extreme tornadoes can attain wind speeds of more than 480 kilometers per hour (300 mph), are more than 3 kilometers (2 mi) in diameter, and stay on the ground for more than 100 km (62 mi).

जमिनीवर कमी दाबाच्या जागेभोवती गोलगोल फिरणाऱ्या हवेमुळे चक्रीवादळसदृश संरचनेस घूर्णवात किंवा टोरनॅडो म्हणतात. घूर्णवातात एका नरसाळ्याच्या आकाराच्या आकाशातून सुरुवात झालेल्या ढगाचे(Funnel cloud) टोक जमिनीला लागलेले असते. हे टोक वेगाने एका ठिकाणापासून दुसरीकडे पळत असते. त्याच्या तडाख्यात आलेल्या घरांचा, झाडांचा आणि इतर वस्तूंचा नाश होतो.