What atmospheric condition often precedes severe weather such as thunderstorms?

Low-level instability is a key atmospheric condition that often precedes severe weather, including thunderstorms. When the lower layers of the atmosphere are unstable, it typically means that warm, moist air is present at the surface and is capable of rising rapidly. This upward movement of air can lead to the development of cumulonimbus clouds, which are associated with thunderstorms. As the warm air rises, it cools and condenses, releasing latent heat, which further propels the storm's development.

In contrast, high pressure systems create stable conditions in the atmosphere with limited vertical motion, making severe weather less likely. Stable atmospheric layers inhibit the upward movement of air, thus preventing the formation of thunderstorms. Clear skies indicate a lack of significant weather activity, often associated with stable atmospheric conditions, and do not suggest an environment conducive to severe weather. Therefore, low-level instability is crucial as it fosters the conditions necessary for the rapid development of thunderstorms.