62-degree Marvin
What you call someone who experiences a noticeable improvement in energy and mood following a change in temperature, from more extreme (hot or cold) to more moderate (a pleasant 62 degrees F).
"Your dad seems like he's in a much better mood since the heat wave broke."
"Yah, he's a 62-degree Marvin."
"Yah, he's a 62-degree Marvin."