Kelvin-Helmholtz (K-H) instability is shear instability that occurs in a stably stratified fluid with strong vertical shear of the horizontal winds. It is well known that a necessary condition for K-H instability is that the Richardson number ( 𝐴𝐴 Ri ) must be <0. 25 (e.g., Miles & Howard, 1964;Scorer, 1969). The Richardson number can be estimated as follows: 𝐴𝐴 Ri = 𝑁𝑁 2 ∕|d𝑼𝑼 ∕d𝑧𝑧| 2 , where 𝐴𝐴 𝐴𝐴 2 is the square of the buoyancy (Brunt-Vӓisӓlӓ) frequency and 𝐴𝐴 |d𝑼𝑼 ∕d𝑧𝑧| is the magnitude of the vertical shear vector of the horizontal winds. The square of the buoyancy frequency is calculated as 𝐴𝐴 𝐴𝐴 2 = 𝑔𝑔𝑔𝑔 −1 d𝑔𝑔∕d𝑧𝑧 , where 𝐴𝐴 𝐴𝐴 is the gravitational acceleration and 𝐴𝐴 𝐴𝐴 is potential temperature. As seen in the 𝐴𝐴 Ri formula, a sufficiently large vertical shear 𝐴𝐴 |d𝑼𝑼 ∕d𝑧𝑧| can initiate instability even if the atmosphere is stably stratified. K-H instability is considered one of the main sources of clear air turbulence that affects the safety and comfort of air travel (e.g., Ralph et al., 1997).