Yours, Etc.: Origins and Uses of 8 Sign-Offs
An upward current of warm, moist air. With enough moisture, the current may visibly condense into a cumulus or cumulonimbus cloud. Compare downdraft.
in meteorology, upward-moving and downward-moving air currents, respectively, that are due to several causes. Local daytime heating of the ground causes surface air to become much warmer than the air above, and, because warmer air is less dense, it rises and is replaced by descending cooler air. The vertical ascending current, called a thermal, may reach an altitude of 3 km (2 miles) or more. The greater the radius of the thermal, the higher it is likely to ascend. Updrafts and downdrafts also occur as part of the turbulence that is created when air passes over topographic barriers such as mountains.