Thunderstorms Thunderstorms associated with approaching frontal systems are characteristically more severe than air mass type thunderstorms.
Cold air is more dense than warm air.
As a cold front approaches a warm air mass, it rapidly lifts the warm air, creating an unstable situation in the troposphere. Frontal thunderstorms that precede a strong cold front often make a dramatic entrance into an area of warm air. You can face the storm and watch as the front approaches. It often appears as a line of dark, rumbling cumulonimbus clouds . Clouds that vertically climb to such heights can be readily identified by their anvil tops, sheared flat by jet stream winds.