One of our neighborhood mail boxes - I think it featured here around eighteen months ago, in sunny summer weather ... today, it was covered in hoar frost. This led to a debate ... is frost a form of precipitation, or isn't it? I argued that it wasn't - and it turns out that I'm right, although I couldn't have told you exactly why - basically it's caused by above-freezing air coming into contact with something below freezing, which causes the water vapor in the air to form fractal crystals on a cold surface. That makes a lot of sense - only I can't imagine that the air was above freezing for long, last night - it was pretty frigid when we woke up, and did our morning stomp around the usual long-ish loop, before I settled back into MLA - with, alas, no cats visible, today.
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