A lapse rate is the rate of temperature change with height. The faster the temperature decreases with height, the "steeper" the lapse rate and the more unstable the atmosphere becomes. Values less than 5.5-6.0 degrees C/km represent stable conditions, while values near 9.5 degrees C/km are considered unstable. Between these values, lapse rates are considered conditionally unstable, meaning that it may become unstable if enough moisture is present. For more information on lapse rates, please click here.