Extreme heat pushing temperatures across the southern United States to 90F threatens an unusually fierce tornado season. Hot air clashing with cold Arctic air dipping into northern States are providing the perfect ingredients for storm formation. Southern and south-eastern regions are prime target areas for tornadoes during spring, but unusual weather this year could drive them further north. March marks the start of twister season which lasts into summer, as cold winter air from the north meets hotter air from the south. This year could spawn more of the destructive storms than usual, thanks …