This is a contour plot of lifted index with a contour interval of 2 degrees Celsius. The LI field shows instability in the atmosphere by lifting a parcel of air from the surface to 500 mb and comparing its temperature to that of the environment. Where LIs are less than 0, thunderstorms are possible. The lower the number, the more unstable the atmosphere is and as a result, the stronger the thunderstorms could become. Values of -4 or lower indicate areas where severe thunderstorms are possible. Values > 10 indicate areas of stable weather where skies are generally clear.
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.
This is a contour plot of CAPE or Convective Available Potential Energy. CAPE represents the amount of energy a parcel might have if it were lifted. Often this reflects the strength of updrafts within a thunderstorm. CAPE values of greater than 2000 represent enough energy to produce thunderstorms. A value greater than 3000 represents enough energy to produce strong thunderstorms. Values < 1000 denote a reletively stable atmosphere.
Text and plots from UNISYS