Based on the information provided about average monthly rainfall during the summer in Boulder, Colorado, and Madison, Wisconsin, the correct conclusion would likely be: "Madison's summer climate is wetter than Boulder’s."
To elaborate, if the graph shows higher average monthly rainfall for Madison compared to Boulder, it indicates that Madison experiences more rainfall during the summer months, making it generally wetter.
The other statements regarding temperature or winter climate cannot be validated without specific data about those conditions. Therefore, only the statement about Madison's summer being wetter than Boulder's can be conclusively supported from the information given.