"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.