Frost Formation

Believe it or not, frost can form when reported temperatures are above 32 degrees F. There are two reasons for this. Number 1: Official air temperatures are taken 5 to 6 feet above the ground. Because cold air is more dense than warm air, the coldest air within the lowest layers of the atmosphere will settle to the ground at night in absence of significant wind. So it can be 35 degrees, for example, where the official temperature is taken and 32 degrees at the earth's surface. The second reason frost can form in situations when the reported temperature is above 32 degrees F has to do with evaporational cooling. When dew forms on vegetation at, say, 35 degrees, it will stay liquid... But only until it begins to evaporate once the sun or wind hits it. Evaporation is a cooling process. So when some of the moisture on vegetation evaporates, it can cool the surface to 32F or below, causing frost to form.