U.S. tornado season is upon us. Tornadoes can occur all year round, but the most likely period in the U.S. is from early spring through summer.
The Where and How of Tornadoes
Tornado Alley is the area that is most often conducive to tornado formation. This area has the highest risk of tornadic activity and stretches from Texas northwards through the Great Plains, and across to the Midwest into South Dakota and southern Minnesota.
Tornadoes are spawned from severe convective storms (often associated with thunderstorms), and therefore can appear all over earth. The capricious mix of very warm and humid air at the surface compared to cold and dry air aloft, and large shifts of wind direction and speed with height is a tornado’s natural habitat, and they will be tempted into existence wherever these conditions occur.
Observing and recording tornadoes is difficult. They are transient and rarely last longer than a couple of hours, but the convective storm systems that generate them can last much longer as they traverse the landscape.
The force of the winds within a tornado will often destroy measuring equipment, so some of the most reliable immediate estimates of wind speeds will come from radar information, looking at movement of raindrops around a rotating core. The radar information and wind measurements used in issuing forecasts and warnings of tornadoes, but it is the damage that occurs within the reach of a tornado that defines the Enhanced Fujita scale value and therefore describes the severity of a tornado.
The best source of tornado information in the U.S. is the Storm Prediction Center, part of the National Oceanic and Atmospheric Administration’s National Weather Service. Their information is based on a variety of sources and is visualised in the hyperlinked map below.
The interactive map shows a year-by-year graph of tornado counts, and includes all reports and tracks with information on individual events such as the human cost, tornado intensity and property loss, as well as track information if available.
Maps such as this can be powerful for quickly understanding the frequency and severity of phenomena such as tornadoes over a large spatial area or intuitively finding data on individual events.
Geospatial tools can help decision-makers understand where their exposures are most at risk, understand correlations between impacts (on life or property) and the spatio-temporal characteristics of severe events.
Ultimately, this can help companies and communities to redistribute their resources and incorporate more intelligent risk management strategies.