[9급 국가직 영어 2015년 10번]

Thunderstorms are extremely common in many parts of the world, for example, throughout most of North America. Updrafts of warm air set off these storms.

(A) This more buoyant air then rises and carries water vapor to higher altitudes. The air cools as it rises, and the water vapor condenses and starts to drop as rain. As the rain falls, it pulls air along with it and turns part of the draft downward.

(B) An updraft may start over ground that is more intensely heated by the sun than the land surrounding the area. Bare, rocky, or paved areas, for example, usually have updrafts above them. The air in contact with the ground heats up and thus becomes lighter, more buoyant, than the air surrounding it.

(C) The draft may turn upward again and send the rain churning around in the cloud. Some of it may freeze to hail. Sooner or later, the water droplets grow heavy enough to resist the updrafts and fall to the ground, pulling air in the form of downdrafts with them.