Investigating the Climate System-Clouds, Weather, Wind, and Precipitation (you can see the links for the others from the Clouds link.)
The Clouds guide is 31 pages, though only pages 3 through 11 are student-related while the rest are for teachers. The premise is that the students have been hired as interns in the State Climatology Office and they need to investigate a letter written to them by a 3rd grader through a series of 5 activities. Each activity is supposed to take around 45 minutes, so this guide alone should be enough to take our co-op to the summer.
I ordered some books about clouds and the water cycle to start us out, and I was excited to find one available by Jeanne Bendick, How to Make A Cloud. I got a couple of generic children's science books, but I found what look to be a couple of nice gems, too.