Final answer:
Sleet forms when raindrops freeze into ice pellets near the ground, whereas hail forms in thunderstorms when water droplets freeze and grow in the updrafts before falling to the ground.
Step-by-step explanation:
Formation of Sleet and Hail
Sleet forms when raindrops fall through a layer of cold air near the ground and freeze into ice pellets before they reach the surface. This usually happens during winter storms when a layer of warm air is sandwiched between two cold layers.
Hail occurs in strong thunderstorms with intense updrafts. When drops of water are carried upwards by the updrafts, they freeze in the cold upper regions of the storm clouds. Successive lifting by the updrafts can cause the hailstones to grow large as they accumulate more and more layers of ice before finally falling to the ground when they become too heavy.
Both precipitation processes involve the cooling and condensation of water vapor, which then forms different types of precipitation depending on the atmospheric conditions they encounter as they fall to Earth's surface.