The dewpoint depression is the difference between the temperature and the dewpoint while the wetbulb depression is the difference between the wet bulb and dry bulb temperature. The dry bulb temperature is the actual temperature while the wet bulb temperature is the temperature air will cool to when water is evaporated into unsaturated air. When the air is saturated, the dewpoint is equal to the wet bulb temperature and the actual temperature. In unsaturated air, the dewpoint is always a lower temperature than the wet bulb temperature because as air is saturated, the temperature decreases while at the same time the dewpoint increases. Wet-bulb cooling can occur at any level of the atmosphere. When it occurs in the middle and upper levels of a thunderstorm, the cooling of the air causes it to become negatively buoyant and that air will accelerate toward the earth's surface causing a derecho, macroburst or a microburst. Wet bulb cooling at the surface can bring refreshing cooler temperatures on a hot summer day and can turn liquid precipitation into frozen precipitation in the cool season. Wet bulb cooling can lower the freezing level in the atmosphere.