I'm building a world from scratch and I was looking for some Earth Science advice.

If I'm trying to be accurate, how much of my world's weather patterns should I figure out before I can drop in biomes?

Any other advice on rules of thumb for climate placement would be helpful to.

Here's what I have mapped out nicely:

  • Mountains
  • Rivers
  • Warm and cold ocean currents
  • Areas where tropical storms tend to form
  • The approximate bands that will be tropical, sub-tropical, temperate, sub-arctic, and arctic


Here's where I'm stuck:

  • Where should grasslands go? When I look at Earth how could I predict that temperate deciduous forests of the eastern United States would give way to the grasslands of the Midwest?
  • Where should deserts go? How can the Arabian Peninsula have bodies of water on three sides and be a giant desert?
  • Why does the African Rain Forest Peter out into savanna around Lake Victoria and then dessert in Kenya and Somalia?



Thanks for any help