K Value or K Index is a measure of thunderstorm potential based on the temperature lapse rate, the moisture content of the lower atmosphere, and the vertical extent of the moist layer. It should be used to analyze the potential for air mass thunderstorm occurrencenot potential occurrences of frontal thunderstorms and not for the potential severity of a thunderstorm. The temperature difference between the 850- and 500-millibar levels is the parameter used to find the vertical lapse rate, and the 850-millibar dew point and the 700-millibar dew point depression are used to evaluate the moisture content of the air, as well as the vertical extent of the moist layer. The K value is found as follows:

Using the K Value as a predictor, you can determine the probability of thunderstorms with the following guidline:

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