Q: Why was there thunder and lightning in the lab?
A: The scientists were brainstorming!
When people brainstorm they make a list of many ideas. Scientists brainstorm ideas for experiments and possible answers or explanations to questions they have. (A lab is a place where some scientists work.)
This joke is funny because it plays with the words storm/ brainstorm.
Here is what a thunderstorm looks like. Remember: do not go out in a thunderstorm!