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.