This is exactly what I was looking for!! perfect for 3 and 4 year olds too!
Weather Activities for Kids: Thunderstorm Art Project (perfect for toddlers, preschoolers, and kindergarteners)~ BuggyandBuddy.com
Rain Painting (Shannon's Tot School) (I'm thinking you could do this with liquid tempera too, for a different look.)
Great letter of the week activities for preschool play groups.
Umbrella Craft with Glue Raindrops. Preschool weather activity for the Letter U. | best stuff