How does snow
The white fluffy snow we see in the winter does not
begin in this shape. The process of forming snow begins high in the
atmosphere in clouds. The amount of moisture and temperature help
determine how snow forms.
Snow begins as a tiny ice crystal, or a speck of
dust. When there is enough moisture in the air, condensation starts to
occur. The tiny drops of condensation start to stick together. If the
temperature in the cloud is cold enough, the tiny drops will freeze and
form ice crystals.
As more crystals stick together, the drops get
heavier and start falling toward the ground. During the fall, the
snowflakes may pass through air pockets that are warmer or cooler. This
melting and refreezing is what gives snowflakes their final shape, like
big soft snowflakes or small fast snowflakes.
Even after the snow reaches the ground, it still
changes shape as it melts or refreezes. If it is very cold, the snow
forms a hard crust on top, or if it is warmer, the snow melts some and
Fog is a type of cloud that can be found at ground
level. It is caused by the super saturation of the air, which means that
the air cannot hold any more water. The water is forced out of the air
and forms condensation. Think of a water bottle sitting on your table.
The water droplets that form on the outside of the bottle are
condensation. This happens in air, except that the droplets float above
the ground. This is what makes the fog.
Four main types of fog exist, and each is formed in
a slightly different way:
Radiation fog is formed as the ground becomes
cooled by the night sky, the air above the ground also cools. If the air
is below its dew point, the point where condensation occurs, fog is
formed. Advection fog comes from warm air moving left to right across a
cool surface, such as when air from a lake blows over the land. The land
cools the air below the dew point causing fog.
Upslope fog occurs when warm air flows up over the
slope of a cool mountain. Again the air cools below the dew point and
forms fog. Evaporation fog is caused by water vapor entering air that is
very close to being supersaturated. The additional water causes the air
to reach the dew point and fog forms.