Here in Big Sky Country, you can often see storms building up over several hours as they move in. When I lived in Ontario, storms were usually part of giant weather front that would be hundreds of kilometres long, stretching down into central United States, and sky would often just get darker and darker until the storm was there. But here, close to the mountains, we don’t see those kinds of systems develop. Instead, it can be lots of big, individual clouds, and with fewer trees and open land, you can see them a long way off!
This storm I was able to watch for over an hour until I was in the right place and at the right time, just before the sun dipped behind the mountains. It had the classic anvil shape until just before I took the pictures when the strong updraft punched over the top.