Hail forms
when the winds in a storm called updrafts are strong enough
to push through the freezing level of a storm. If an updraft
extends far above the freezing level, then raindrops and water
vapor can freeze. Frozen water droplets can blow around to different
parts of a storm, and accumulate more water and re-freeze many
times before it is heavy enough to fall to the ground.
Sleet: Rain that
turns to ice pellets before reaching the ground. Sleet also
causes roads to freeze and become slippery.
Sleet is precipitation
of small, partially melted grains of ice. As raindrops fall
from clouds, they pass through layers of air at different
temperatures. If they pass through a layer with a temperature
below the freezing point, they turn into sleet. Snowflakes
that have melted by passing through a warm layer will turn
into sleet if they then pass through a freezing layer. Sleet
often falls together with snow and rain, and may deposit an
icy coating on exposed surfaces. Sleet occurs only during
the winter, while hail, a different form of icy precipitation,
may fall at any time of the year.
