Use this calculator to explore the effect of temperature on the buoyancy of a parcel of air (think about a large balloon to visualize a parcel of air). The buoyancy depends on two variables:
The buoyancy of the parcel of air and the Lifted Index (L.I.) are calculated by this calculator. A negative buoyancy means that a parcel of air lifted will tend to sink back down to where it started, while a positive buoyancy is just the opposite.
The Lifted Index is calculated by lifting a parcel of air dry adiabatically while conserving moisture until it reaches saturation. At that point the parcel is lifted moist adiabtically up to 500mb. The Lifted Index is the ambient air temperature minus the lifted parcel temperature at 500mb. If the parcel is warmer than the environment (negative L.I.), it has positive buoyancy, and will tend to continue to rise, favoring convection. L.I. values less than -5C indicate very unstable conditions. A positive L.I. value indicates negative parcel buoyancy, and the parcel will tend to sink. This is representative of stable conditions where convection is unlikely. Increasingly negative numbers correspond to increasing instability and likelihood of severe weather. At times, very high (stable) lifted index values in cold air are indicative of frozen or freezing precipitation versus rain during warm advection events. The extreme stability does not allow air to lift out, resulting in cold air "damming", which restricts the advance of warm air at the surface.
Buoyancy