It's because he's dying. His happiest memory/memories were when he created storms with Lanho and the rest of his children, so now he's obsessed with recreating that, and thats also why he was so obsessed with our babe, Beom, and why he desperately tried to turn Beom's father before that.
I’m kinda confused with Roberts obsession with snow like was it because of the other guy his “son” or those he just like quite things