Types of Precipitation

colder clouds, ice crystals can bump into one another, destabilizing them so they break into even smaller pieces. These smaller pieces act as seeds to make more ice crystals. Through the process of aggregation, ice crystals collide and clump together to form what we now know is a snowflake. You need at least 100,000 times to 1 million times more water droplets in a cloud than ice crystals in order to get snow.

TYPES OF PRECIPITATION

Let's look at the different types of precipitation you might see:

• Rain – as you know, being can be 0.02 inches or more in diameter. You can have smaller droplets of rain then this if they are widely separated; otherwise it would be called drizzle.

• Drizzle – these are very fine drops of rain that are fairly close together and seemed to float in the air as they fall gently to the ground. The drops are of uniform shape and size and, if any smaller, might be suspended in the air as you see in fog.

• Ice pellets or sleet – these are small transparent ice pellets which are fairly round and hard to the touch. You can think of them as small grains of ice or frozen raindrops. It is also possible for them to be snowflakes that melted and then refroze.

• Hail – you know these as balls or clumps of ice that are at least 5 millimeters or one fourth inch in diameter. Should hail become greater than one inch in diameter, this is relatively severe and can cause a lot of damage on the earth's surface. These large hail clumps are seen with severe thunderstorms. The largest documented hail stone was found in South Dakota to be 8 inches in diameter.

• Snow pellets – these are also called small hail. By definition, the diameter is less than 5 millimeters or less than one fourth inch. They tend to be much more opaque than hail and can be of varying shapes, although they are usually spherical.

• Snow – snow is of course snow crystals that have the typical hexagonal shape in the form of a 6 pointed star. This shape is because it is the shape of microscopic ice crystals that then grow to be a crystal of snow you see as a snowflake.

• Snow grains – this is essentially frozen drizzle. These are extremely small grains of ice that are white or opaque. They are smaller than ice pellets with a size that is approximately one millimeter in diameter or less.

• Ice crystals – these tend to be seen only in extremely cold regions around the earth. Another name for them is diamond dust. They can be shaped like columns, plates, or even needles. They are so fine that looks like fog, except that these will fall to the ground. There is an optical illusion they create called an ice pillar, which comes from artificial light on the ground as shown in figure 20:

Figure 20.