Snow wasn’t simply freezing rain, the cloud itself had to freeze such that tiny crystals clumped together, and the area around had to be cold enough that they didn’t melt when they fell. Adding moisture and rain to the cloud would have to be Thor’s job in addition to corralling the thing in the first place.

But the freezing, that Loki could do. Once again he yanked at the resistance to the freezing power through the staff (was it actually easier, or just in his head?) and pointed the staff at the cloud. Again the runes flared as soon as the resistance broke, and the water in the cloud turned to tiny ice crystals while Loki radiated freezing cold.