Convection- The process whereby warm air rises in columns upwards through cooler surrounding air. Convection is a big part of the 'engine' in thunderstorm development, pulling massive volumes of moisture (water vapor) in warm air into the cooler air above, allowing condensation of the water vapor into towering storm clouds (cumulonimbus). Convective activity is likely to occur when the atmosphere is unstable and/or when a strong 'forcing element' such as a cold front is present (a cold front acts like a horizontal 'wedge' as it moves, forcing air ahead of it to rise). Thunderstorm activity is also sometimes called 'convective' activity.