The fluffy cumulus clouds form first as the moisture in the warm air updraft hits the cooler dry winds and condenses. The condensation releases latent heat, which creates energy, which creates more vertical speed, which sucks in more warm, moist air, which forces the cooler air to sink ever faster, and the cycle begins. The cumuli begin to fatten and darken. The warm air updraft builds on a column of condensing particles, and the tower of clouds bubbles 30,000 to 40,000 feet in a matter of minutes. The cumulus has become the cumulonimbus, the thunderstorm cloud—Cb in meteorology shorthand.
