Sunset Color Prediction

I have a project for a client that requires me to photograph a spectacular sunset at a specific location - I have been watching the clouds all summer trying to determine when a good time to photograph will be. I have found the best sunsets often occur in the autumn and winter months, but I wanted to share this useful link from photo.net about predicting sunsets. Any other people with insights on this topic are welcome to comment to this post. I have found the iphone software focalware is great for predicting the time and location of a sunset, now if someone would write an app that predicts how colorful it would be based on cloud cover, etc that would be great.