The temperature difference between 850 mb and 500 mb is used to parameterize the vertical temperature lapse rate. The 850 dew point provides information on the moisture content of the lower atmosphere. The vertical extent of the moist layer is represented by the difference of the 700 mb temperature and 700 mb dew point. This is called the 700 mb temperature-dew point depression . The index is derived arithmetically and does not require a plotted sounding.
Threshold values vary with season, location, and synoptic situation.
The following table shows what various K-indices mean. K-indices are also used to determine the potential of flooding. If these thunderstorms track across the same area, you may have a various serious flooding situation on your hands. Factors in the index are maximum daily temperature, daily precipitation, antecedent precipitation, and annual precipitation. Typical of spring dormant season following winter precipitation.