Ken Snodgrass of Baltimore asks: "Why, sometimes, does dew/frost form on my front and back car windows but not on any of the side windows?" You stumped this chump. Frost forms when skies are clear, winds calm. Glass radiates heat into space and cools, condensing water vapor into dew, or frost crystals. Bill Syrett of Penn State Weather Communications tells me heat radiates upward. So glass more parallel to the ground gets colder, faster than vertical glass, which retains heat rising from below.