The dew point depression (T-Td) is the difference between the temperature and dew point temperature at a certain height in the

atmosphere An atmosphere () is a layer of gas or layers of gases that envelop a planet, and is held in place by the gravity of the planetary body. A planet retains an atmosphere when the gravity is great and the temperature of the atmosphere is low. A s ...

. For a constant temperature, the smaller the difference, the more moisture there is, and the higher the relative humidity. In the lower troposphere, more moisture (small dew point depression) results in lower cloud bases and lifted condensation levels (LCL). LCL height is an important factor modulating severe thunderstorms. One example concerns tornadogenesis, with tornadoes most likely if the dew point depression is 20 °F (11 °C) or less, and the likelihood of large, intense tornadoes increasing as dew point depression decreases. LCL height also factors in downburst and microburst activity. Conversely, instability is increased when there is a mid-level dry layer (large dew point depression) known as a "

dry punch A dry punch is meteorological slang for a synoptic scale or mesoscale process. A dry punch at the surface results in a dry line bulge. A dry punch aloft above an area of warm, moist (buoyant) air at low levels often increases the potential for sev ...

", which is favorable for convection if the lower layer is buoyant. As it measures moisture content in the atmosphere, the dew point depression is also an important indicator in agricultural and forest meteorology, particularly in predicting wildfires.

See also