Ororo Munroe, AKA Storm, is easily one of the most powerful X-Men out there. There's a good reason that she was, at one point, worshiped as a goddess. Being able to control the weather itself is no small feat. Luckily, Storm has a strong moral compass,
and incredible leadership capabilities. But what if she switched sides?
The only thing that "limits" Storm's ability to control the weather is that she doesn't want to endanger innocent lives. If that ceased to be a concern, she could easily create tornadoes, blizzards, hurricanes, or any manner of potentially catastrophic weather patterns, at any time, and wipe out entire towns in mere minutes. There'd be no way to take her on, as anyone that opposed her could be easily swept away. Seriously, as a villain, Storm would be almost unstoppable.