An outbreak of 69 confirmed tornadoes during the last four days of April, 2014, took 35 lives and caused over $1 billion in property damage. Two Arkansas towns north of Little Rock – Vilonia and Mayflower — were the hardest hit. The rash of tornadoes also devastated communities in Oklahoma, Kansas, and Texas.
Tornadoes kill an average of 60 people a year in the US, according to NOAA. This varies greatly by year. 2011 was one of the most destructive and deadly on record. An F4 tornado with wind speeds of 200 mph (322kp/h) wiped out Joplin, Missouri, killing 162. Earlier that year, an F-4 struck Tuscaloosa, Alabama, killing 65 and leveling a wide path through part of the city. Total fatalities for all tornadoes that year were 551, with damages estimated at $28 billion.
Tornadoes are a product of high-energy cloud formations called supercells. In the spring, when warm, moist air flows into the Midwest and Southeast from the Gulf of Mexico, it rises and mingles with layers of cooler, drier air coming in from Canada and the mountain west. The warm air condenses when it meets the cool air, forming cumulus clouds. Rising convection currents create energy and instability inside the cumulus formation. When the energy level peaks high enough, a rotating updraft or mesocyclone develops and the storm formation becomes a supercell. In some cases, the energy moves vertically down from the base of the supercell to the ground in the form of a spinning vortex.
There are several mysteries about tornadoes. Scientists know generally how they form and what happens once they do, but do not know why some storm clouds morph into supercells and most do not. Also, once a cumulus buildup turns into a supercell, why do 30% produce tornadoes, and 70% only rain or hail? Even though the National Weather Service has gotten quite good at forecasting tornadoes in a specific area, the behavior of a tornado once it touches down is not always predictable. Tornado paths range in width from 100 yards (91m) to 2.6 mi (4.3km), and the length from 10 miles (16km) to hundreds of miles. They can last from a few seconds to more than an hour. They move across the land in a northeasterly direction at between 30 mph and 70mph (48 to 112kp/h).
Not all states in “Tornado Alley” have building codes that require storm shelters in schools and hospitals, where many of the casualties have occurred in past tornadoes. If more states included that in their building codes, it would undoubtedly save lives in the future.