Abstract
Cumulonimbi are often reported in cold air during winter months in northern Europe but thunderstorms are observed much less frequently. This suggests that some cold air cumulonimbi cannot develop into thunderstorms. The possibility of identifying cumulonimbi lacking thunderstorm potential is investigated. Threshold height and temperature values are found for cold air thunderstorms. Approximately 10% of soundings associated with cold air cumulonimbi have values below this threshold. Also, chi-square tests of a Revised Stability Index based on threshold values indicate that some cumulonimbi are not unstable through sufficient depth to develop into thunderstorms. A stability cutoff value is established which separates “stable” cumulonimbi from others which have the potential to become thunderstorms.
