From the Rockies across the Great Plains to the Great Lakes, a dangerous storm system is building up. A cold front is triggering turbulent weather with many severe thunderstorms.

Conditions will be particularly severe from Kansas to south-eastern Nebraska. Supercells may form there, producing giant hailstones and powerful tornadoes. These are long-lived, rotating thunderstorm cells with strong updrafts.

At the same time, warm, moist air is flowing far northwards from the Gulf of Mexico. Meanwhile, cooler air is moving in from the north-west, providing the thunderstorms with additional energy.

As well as tornadoes, there is also a risk of heavy downpours, strong gusts of wind and localised flooding. Conditions may remain unsettled in some regions until Wednesday.