K and Modified K index

[jrleeman]

Parameter used to indicate the potential of air mass thunderstorms.

From COD (http://weather.cod.edu/sirvatka/si.html)

K-Index

K = (T850 - T500) + Td850 - (T700 - Td700)
The K index is a poor indicator of severe thunderstorms since dry air at 700 mb may indicate convective instability. Dry air at 700 mb will give a low value to the K-Index.

K values +20 indicate some potential for air mass thunderstorms.
K values +40 indicate almost 100% chance for air mass thunderstorms,
with values over +30 to indicate potential MCC's.

Modified K-Index

Similar to that of the K-Index except that instead of the T and Td at 850 mb, the average temperature and dew point between 850 mb and the surface are used.

[dopplershift]

Still need modified k-index.