Thunderstorm season is beginning in the US. On Thursday and Friday, the risk of severe weather will increase significantly in the south and Midwest.

This can lead to the formation of individual supercells with large hailstones and severe squalls. Tornadoes cannot be ruled out in organised thunderstorm lines.

The regions from North Texas to Oklahoma and Kansas are particularly at risk. But parts of Nebraska, Illinois and Indiana could also be hit hard.

This is caused by warm, humid air from the Gulf meeting colder air from the north. A low-pressure system is adding extra dynamism to the weather. Its distinctive cold front, which is moving from the north-west to the south-east, is causing a drop in temperature.