Atmospheric soundings provide twice daily vertical profiles of the troposphere and lower stratosphere. The lapse rate is calculated from this profile as the rate of temperature change with height. The featured chart presents the monthly distribution of the lapse rate between 850 and 500 hPa (millibar) pressure levels for the Omaha sounding site. This is roughly from a typical cloud base to midway vertically through the cloud. When this lapse rate is below 6 °C per kilometer, the atmosphere is in a stable condition meaning vertical temperature gradients are not large enough to drive robust motions due to buoyancy. When values are between about 6 and 9.5, the atmosphere is conditionally unstable and vertical motions are likely to occur. Values above about 9.5 are said to be absolutely unstable and vertical mixing will happen quickly. The chart shows the strongest instabilities during the summer season, which is also the time of year for thunderstorms. Of course, there is a direct relationship between thunderstorms and lapse rates. Stability increases (lower lapse rate) in the winter time and so we see fewer thunderstorms. For comparison, recent lapse rates have been in the mid 5s, which is not high enough for robust storms.

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