K Index - -12 hr
This is a contour plot of K index with a contour interval of 4. The KI field shows instability in the atmosphere as it relates to the development of air mass thunderstorms. It is based on the 850 to 500 mb lapse rate plus 850 mb dewpoint minus the 700 mb dewpoint depression. Strong Springtime thunderstorms often require dry air at mid levels to cap the convection. On the other hand, summer air mass thunderstorms need a very moist atmosphere at mid levels to prevent evaporation through entrainment. Where KIs are greater than 35, air mass thunderstorms are likely. the higher the number, the higher the probability. Values <10 indicate areas of stable weather where skies are generally clear.