A temperature below freezing refers to a temperature at which water freezes, which is 0°C, 32°F, or 273 K. This temperature is usually measured at a height of 1.2 meters above the ground surface. However, it is important to note that frost can form even when the official temperature is above freezing, since the ground temperature can be colder than the air temperature. Additionally, frost will only form if the ground temperature matches the dew point. In terms of precipitation, if the temperature of the atmosphere from cloud-bearing altitude to the ground is below freezing, precipitation will be snow. If it is above freezing from the surface to roughly 1,000 feet or more above, it will rain. If rain from an above-freezing layer aloft falls onto a sub-freezing surface, then the result will be freezing rain.