Placing Global Biomes/Terrain/Vegetation - Rules of Thumb?

[delguidance]

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

[Mapsburgh]

Cllimate is the biggest determinant of biomes, so if you want to get your biomes right, it pays to figure out your climate first.

Grasslands are largely driven by moisture. The Great Plains are grassland because they lie in the rain shadow of the rocky mountains. Farther east, moisture comes up from the Gulf of Mexico to allow for forests.

The Arabian Desert is created by the subtropical high -- a band of high pressure that sits at about 30 degrees N and S latitude. That's the same as the Sahara, Sonoran, Kalahari, and Australian deserts. You would expect to have deserts at about that latitude all around your world.

[delguidance]

Hey thanks!

Pittsburgh? I'm over in Westmoreland County in Irwin! Small digital world. Since posting I saw some great climate tutorials in this forum.