Definition: A tornado is a violently rotating column of air extending from a cloud and in contact with the ground.
Funnel Cloud: If the rotation doesn't touch the ground, it is known as a funnel cloud.
Verification: Tornadoes must be visually verified either by trained spotters or post-event damage surveys.
Detection and Visibility
Doppler Radar: Useful for detecting atmospheric rotation but cannot confirm ground contact.
Visibility: Tornadoes may not always be visible due to condensation variability.
Formation
Tornadoes primarily form from severe thunderstorms and hurricanes.
Other rotating columns include dust devils, fire tornadoes, gustnadoes, and waterspouts.
Characteristics of Tornadoes
Size and Speed: Most are less than half a mile wide, track 2-4 miles long, and move at ~35 mph.
Measuring Tornado Strength
Fujita Scale: Introduced in 1971 to estimate wind speed via damage assessment.
Enhanced Fujita Scale (EF Scale): Includes additional damage indicators, like building structures. Direct wind speed measurement during a tornado is rare.
Notable Measurement: 318 mph wind speed measured in 1999 Oklahoma City F5 tornado.
Global Occurrence
Tornadoes happen worldwide, including all U.S. states and countries like Canada, Argentina, Bangladesh.
The U.S. averages 1,200 tornadoes annually, with many in the Great Plains, and more violent ones in Dixie Alley.
Seasonal Patterns
Tornadoes generally occur during the warm season but can occur any month.
Peak in U.S.: May, often in early evening.
Migration: From the Gulf of Mexico to Canada as solar energy shifts north.
Tornado Outbreaks
Defined as 10+ tornadoes from the same storm system (families).
Notable Outbreak: April 27, 2011, known as the Super Dixie outbreak, ranks second in severity.
Tornado Formation Process
Supercells: Primary producers of tornadoes; only 10% generate tornadoes.
Wind Shear: Change in speed or direction of wind, facilitates rotation.
Updrafts: Uplift tumbling winds to initiate vertical rotation.
Supercell Structure
Mesocyclone: Rotating system within supercells, usually 2-6 miles wide.
Inflow Bands: Low-level cumulus clouds showing air intake.
Wall Cloud: May indicate tornado formation.
Tornado Life Cycle
Stages: Includes formation, mature, and dissipation stages.
Track: Typically follows the storm system path, SW to NE in the U.S.
Safety and Damage
Major Dangers: Flying debris and falling structures.
Safety Locations: Below ground structures and safe rooms.
Vehicle Risk: Cars are not safe due to wind lifting potential.
Radar and Forecasting
Radar has been crucial in tornado detection since the 1973 Union City tornado.
Forecast Improvement: 30-minute warning times are typical, but understanding of outbreak conditions is still developing.
Conclusion
Tornadoes are complex meteorological phenomena with specific formation processes and widespread impacts.
Continued research aims to improve forecasting and safety measures.