Hard Freeze, But No Frost: What Gives?
March 27, 2012
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When I got up this morning, it was 19F, but I saw a sight similar to this one. No frost on the ground at all.
ery early this morning, the temperature bottomed out at 18F, so my max-min thermometer tells me. And yet, when I looked out my window, there was not a speck of frost on the grass. If I hadn’t consulted the thermometer, I would have thought it was a lovely spring day out there. (The grass has grown up and is even greener than depicted in the photo above, which was taken about two weeks ago.)
How can that be? Some of you may already know the answer, but I asked the National Weather Service office in Binghamton, NY just to be sure, and they confirmed my suspicions. The air was very dry and the dew point was even lower than last night’s low. To refresh your memory, the dew point is the temperature at which the moisture in the air condenses onto surfaces such as the grass. If the dew point is lower than the air temperature, then even if the air temperature is below freezing, you won’t see any frost.
Dry air and low dew points are typical for winter, but most of the time the ground is snow-covered (at least around here) and we don’t notice the lack of frost. This was just one of those times when it was cold and dry but not snow covered–and the lawn was lushly green, making the absence of frost even more noticeable.
The Dew What? What Is The Dew Point?
A Gardener’s Guide to Frost: Outwit the Weather and Extend the Spring and Fall Seasons
. . . the difference between great daffodils and common ones is not so vast as one thinks in the first flush of excitement when one starts being serious about daffodils.
in The Essential Earthman: Henry Mitchell on Gardening