The point on a thermodynamic diagram where a sounding curve (representing the vertical distribution of temperature in an atmospheric column) intersects the saturation mixing ratio line corresponding to the average mixing ratio in the surface layer (approximately the lowest 500 m). The dry adiabat through this point determines, approximately, the lowest temperature to which the surface air must be heated before a parcel can rise dry-adiabatically to its lifting condensation level without ever being colder than the environment. This temperature, the convective temperature, is a useful parameter in forecasting the onset of convection (AMS online).