Stability Assessment » K Index (KI) Skew-T Procedure
From the sounding, read the temperature and dewpoint values at 850 and 700 hPa, and the temperature at 500 hPa, and use them to compute the K index as follows:
K index = (T850 - T500) + Td850 - (T700 - Td700)
If the surface pressure < 900 hPa, then use the temperature and dewpoint at 800 hPa instead of 850 hPa.