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Gfs Soaring Index (K-Index)                                                   source:http://www.wetter3.de


Convective clouds = grey lines with values in %.

Soaring(K)-Index = values in color

K Index calculator



Enter the 500 hPa temperature (°C)
Enter the 700 hPa temperature (°C)
Enter the 700 hPa dewpoint (°C)
Enter the 850 hPa temperature (°C)
Enter the 850 hPa dewpoint (°C)
The K Index is


KI <20:         thunderstorms unlikely.
KI 20 to 25: isolated thunderstorms.
KI 26 to 30: scattered thunderstorms.
KI 31 to 35: few thunderstorms.
KI 36 to 40: few to numerous thunderstorms .
KI > 40:        almost 100% risk for thunderstorms.

The K Index is primarily used to forecast heavy rain and thunderstorm potential. It ain't a good predictor for severe vs non severe weather. The K Index was developed for pulse (air mass) thunderstorm forecasting. It works best used in summer period for air mass thunderstorms (no dynamical triggering mechanism).

Tests on the field showed there is a good correlation between no occurrence of thunderstorms and KI values <26.

Formula: K = (T850 -T500) + Td850 - (T700-Td700).



a. May not pick up a capping inversion that prevents storms from developing.
b. Index should not be used to determine severity of storms.
c. VT may be very high and contributes to causing a high KI even when moisture is lacking. Index will be unrealistically too unstable in these situations.
d. Works best for flat areas in low to moderate elevations. Does not work for high elevations.
e. Index value interpretation varies with season and location.
f. 700 mb dewpoint depression may be very large and thus will lead to a stable KI. Very dry air at 700 mb will not degrade the convective potential as long as there is moisture below this layer. KI is better to use when forecasting within a deep layer of mT (maritime tropical) air as opposed to adifferential advection situation in which an elevated mixed layer advects over mT air.