Legend. KO Index = blue lines with values. (S = >+6 = stable, L = < -6 = unstable). Vertical motion forced by dynamical forcing at 500 hPa = zones in color (hPa/hour).   Critical values KO. > 6: no potential risk thunderstorms. 2-6: small potential risk for thunderstorms. < 2: potential risk for thunderstorms. Vertical motion: large negative values = strong ascent   Combination of both: Stable KO region + negative motion = frontal zone. If the negative motion is positioned on a strong gradient in the KO indices between a stable and unstable zone: front is potentially unstable with risk for severe embedded thunderstorms Unstable KO region + negative motion = active upper trough with risk severe thunderstorms Unstable KO region without negative motion = air mass instability which may produce thunderstorms due to diurnal heating (mainly in the afternoon)

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