"it is snowing in London" (if it is snowing now). if you speak in general, that sometimes it snows, then "it snows in London" is OK

1. London Snows! This is OK if you are using this as a new headline. Otherwise, "London is snowing" 3.the weather snows in London Snowy weather in London. 最好有份中文版, 可以正确帮你表示你的意思

It snows in London. (fact that happens normally or usually). It is snowing in London. OR It's snowing in London. (means right now!)

The second one

"It snows in London" is the only right way to say it from the ones you posted. But there are other ways to say it DEPENDING on context: Snow falls in London after 100 years of only heavy rains. 1.london snows = incorrect, but you can say "London welcomes winter time with car-stranding heavy snow". 2.it snows in London = correct. 3.the weather snows in London = incorrect, but you can say "The weather in London is so cold during the winter that it snows every day" Hope this helps.