What does a lapse rate less than 5.4 degrees F suggest?

A lapse rate of less than 5.4 degrees Fahrenheit per 1,000 feet suggests that the atmosphere is stable. This stability indicates that the temperature decreases at a rate slower than the typical lapse rate, which is approximately 3.5 degrees Fahrenheit per 1,000 feet in the lower atmosphere.

In a stable atmosphere, rising air parcels tend to remain colder and denser than the surrounding air, which inhibits their upward movement. This means that if an air parcel does rise, it will cool down more quickly than the surrounding air due to the lower lapse rate, leading to a condition where the air does not continue to rise on its own.

A lapse rate greater than the standard lapse rate (typically around 5.4 degrees F) would generally indicate instability in the atmosphere, which is conducive to vertical movements of air, such as the development of thunderstorms or other weather phenomena. Conversely, a lapse rate less than this threshold suggests a lack of vertical mixing and promotes stable air conditions, leading to a more uniform and calm atmosphere.