英语翻译A front occurs when cool,dry air from the north meets wa

英语翻译
A front occurs when cool,dry air from the north meets warm,humid air coming from the south,from the Gulf of Mexico,for tornadoes in the United States .
文章讲的是tornado的形成,请问,其中,for tornadoes in the United States怎么理解?是不是指美国地区形成的tornado,是由于北部的干冷风遇到的南部墨西哥海湾的湿热风所形成的的峰而形成的.