I found what may have been a minor glitch - the base map did not have Prescale editing enabled, so the steps that used it probably didn't happen. I'm re-running the script now just to see what it looks like. I think I'm also going to double the amount of continental drying. Rather than drop it 1" per 10 pixels, I'll drop it every 5 pixels.

I know that central valley around the lake has incorrect rainfall - it's entirely surrounded by mountains, and would most likely be in a permanent rainshadow. But I haven't figured out a way of automatically calculating rainshadows, so fixing that would be a manual process, and that's not what I'm aiming for with this project. I'm trying to build up a complete automatic script that I would run before doing any hand-editing. Now, if anybody knows of a way to automatically figure out rainshadows or wind/ocean currents, that would be completely different....