Both autumn and spring are transition seasons between the warmth of summer and the chill of winter. And there are some similarities in temperature between those two seasons - roughly speaking, November's temperatures around here are comparable to March's, October's to April's, and September's to May's.

But our weather in spring tends to be more volatile than in fall: spring is windier, with more thunderstorms, and spring tends to be a little wetter as well. We can explain this difference using the fundamental principle known as "stability."

When you're loading a moving van, a cardinal rule is to put the heavy things on the bottom, and the lighter things on top. If you put the heavy stuff on top, the whole pile is in greater danger of crashing down. You could say that the pile has greater "stability" if the heavy stuff is on the bottom. In the atmosphere, the "heavy stuff" is colder air, while warmer air tends to be lighter. How does this help explain the differences between spring and fall? I'll answer that tomorrow night.

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