Listener Question: Strange Car Frost |
 Dave Thurlow, Host |
Hi I'm Dave Thurlow for the Mount Washington Observatory. Today on the Weather Notebook a question from a listener:
"Hi, this is Rob Norton from Boscawen, NH and I think I have a real poser for your guys. Some mornings when the weather's changing, when fall is turning to winter, before it gets really, really cold at night, I'll go out in the morning, just like I did this morning, and have to scrape off the front window of my car and the back window, but the sides are not frozen.
There's condensation on them, they're wet, but it's not frozen, even on the side away from the house. And I wonder if you guys can figure this one out and give me an answer as to why this is happening. It really does happen, no one believes me, I hope you guys do (laugh)."
Believe you? Of course I believe you because I've seen it myself. See, the front and back windows of a car are closer to being horizontal. That means they can lose heat straight up to space, there's nothing above them reflecting heat back down. So the heat radiates to space, that's called radiational cooling, so the front and back windows are able to cool down just a little bit more, so frost forms quicker. Quicker than the side windows which are up and down and they radiate sideways.
Frost occurring on the front windshield. Notice the side windows are clear.
This means that there's not a lot of the window pointing towards space and so it doesn't cool as quickly because there are things in the environment like trees, the ground, and far away buildings that are actually radiating heat towards the sides and keep the condensation from freezing. So, I'll bet if the night was just a teeny bit longer, frost would actually form on the side windows too.
If you want to ask a question, please feel free to call us here at 1-888-RAIN-001. Support for The Weather Notebook comes from Subaru and the National Science Foundation.