K-Index is a measure of thunderstorm potential based on the vertical temperature lapse rate, and the amount and vertical extent of low-level moisture in the atmosphere.

K= 0 to 18 |
Stable. No Thunderstorms |

K= 19 TO 20 |
Marginally unstable. Thunderstorms Unlikely. |

K= 21 TO 25 |
Moderately unstable. Isolated Thunderstorms. |

K= 26 to 30 |
Widely Scattered Thunderstorms |

K= 31 to 35 |
Numerous Thunderstorms |

K= 36 to 40 |
Very Unstable. Thunderstorms Very Likely |

K=> 40 |
Extremely Unstable. 100% Chance of Thunderstorms |

Other UKAWC Stability Indices:

Lifted Index (LI) | CAPE | CIN | Showalter Index | SWEAT | Total Totals |