A relentless spring unleashes deadly tornado outbreaks

A relentless series of powerful storm systems swept across the central and southern United States this spring, spawning hundreds of tornadoes over several weeks in one of the busiest and most destructive stretches of severe weather on record.

Outbreak after outbreak tore through the Plains, the Midwest and the South, with some days producing dozens of tornadoes, including violent, long-track twisters that flattened neighbourhoods and small towns. The storms killed dozens of people and left widespread destruction across multiple states.

The season's ferocity was driven by a persistent clash of warm, moist air flowing north from the Gulf of Mexico with cooler air aloft and strong winds, a recipe for the rotating supercell thunderstorms that produce the most dangerous tornadoes.

Forecasters at the national storm prediction centre issued repeated high-level warnings, and advances in forecasting gave communities more lead time than in past generations, likely saving lives even as the sheer number of storms overwhelmed some areas.

The relationship between climate change and tornadoes remains an area of active research, more complex than for heat or heavy rainfall. But scientists have noted shifts in where and when tornado outbreaks occur. Whatever the long-term trends, the spring was a punishing reminder of the destructive power of severe thunderstorms and the importance of heeding warnings when the sky turns threatening.