Here is the complete sentence: In the great plains of the U.S., tornadoes are common in the summer. This is because, WINDS PICK UP SPEED MORE GRADUALLY IN THE SUMMER.
The Great plain of US refers to the broad expanse of land that lies to the west of Mississippi River and east of the mountains of US and Canada. The region transverses more that nine states in the US and cover portions of two countries.The major part of the land can be described as grassland. The region has a continental climate and is always hot in the summer; during this period tornadoes is common in the area as a result of storms that are characteristic of the period.