Temperature Lapse Rate Calculator

The environmental lapse rate (ELR) is the actual rate at which temperature decreases with altitude in the atmosphere at a given time and place. It is measured from radiosonde soundings and can vary widely from super-adiabatic (highly unstable) to inverted (temperature increasing with altitude). It differs from the dry and moist adiabatic lapse rates, which describe how an air parcel cools when lifted.

The International Standard Atmosphere (ISA) defines a lapse rate of 6.5 C per 1,000 meters (approximately 3.6 F per 1,000 feet) in the troposphere, up to the tropopause at approximately 11 km. This is an average; actual lapse rates vary with season, latitude, and weather conditions.

When the environmental lapse rate exceeds the dry adiabatic lapse rate (9.8 C/km), the atmosphere is absolutely unstable and will spontaneously overturn. When the ELR is between the moist adiabatic (approximately 6 C/km) and dry adiabatic (9.8 C/km) rates, it is conditionally unstable, meaning lifted saturated parcels will rise freely. When ELR is less than the moist adiabatic rate, the atmosphere is absolutely stable.

A temperature inversion occurs when temperature increases with altitude rather than decreasing, giving a negative lapse rate. Inversions trap pollutants and moisture near the surface, suppress convection, and are common at night (radiation inversions) and below subsiding air in high-pressure systems. Inversions above the surface are called elevated inversions or subsidence inversions.

A steep mid-level lapse rate (above 7-8 C/km between 700 and 500 mb) is a key ingredient for severe thunderstorm development. It allows convective updrafts to accelerate rapidly once they become positively buoyant. The Storm Prediction Center monitors mid-level lapse rates as part of their severe weather parameters.