Merry Xmas, it’s frosting tonight!!

FRIDAY MORNING UPDATE: a touch of frost occurred on Thursday morning, just a little hint. It’s now Friday morning, and there is no frost. In fact, it’s simply not as cold outside as it was yesterday. The first night of frost ought to be followed by a string of frosty nights, in the still night valley air, and the temperature has clearly recovered.

I was talking about frost the morning after Halloween when I was a kid, then the first night of frost retreating to mid-November ever since. Well, tonight, leaving work, at a mere 1 am, with hours of cold, still, dry night left to go, the car roof was covered with a strange substance: frost! Now, this is as opposed to freezing air temperature. Frost is when surfaces like metal and grass blades dip below the freezing point, collecting ice from the night air. The air is still a little active with a light northwesterly breeze, and that will keep the frost from covering much more than car roofs exposed to open sky and will keep the air temperature above freezing by mixing in naturally warmer air from higher off the ground with the colder air near the ground in contact with the surfaces that are radiating their energy into outer space, a process called “radiative cooling”.

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