K-index (meteorology)
K-Index in meteorology is a measure of the thunderstorm potential based on vertical temperature lapse rate, moisture content of the lower atmosphere, and the vertical extent of the moist layer.
The index is derived arithmetically: K-index = (850 hPa temperature - 500 hPa temperature) + 850 hPa dew point - 700 hPa dew point depression
- The temperature difference between 850 hPa and 500 hPa is used to parameterize the vertical temperature lapse rate.
- The 850 hPa 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 hPa temperature and 700 hPa dew point.
| K-index values vs. Thunderstorm Probability | ||
|---|---|---|
| K-index value | Thunderstorm Probability | |
| Less than 20 | None | |
| 20 to 25 | Isolated thunderstorms | |
| 26 to 30 | Widely scattered thunderstorms | |
| 31 to 35 | Scattered thunderstorms | |
| Above 35 | Numerous thunderstorms | |