Precipitation is any form of water particle, whether liquid or solid, that falls from the atmosphere and reaches the ground.

The process of continuous condensation in free air helps the condensed particles to grow in size. When the resistance of the air fails to hold them against the force of gravity, they fall on to the earth’s surface.

So after the condensation of water vapour, the release of moisture is known as precipitation. This may take place in liquid or solid form.

Rainfall

The precipitation in the form of water is called rainfall. Most commonly observed; water drops larger than drizzle (0.02 inch / 0.5 mm or more) are considered rain.

However, smaller drops are also considered raindrops if, in contrast to drizzle, they are widely separated.

Drizzle

Fairly uniform precipitation composed exclusively of fine drops very close together.

Drizzle appears to float while following air currents, but unlike fog droplets, it falls to the ground.

Quite often, fog and drizzle occur together.

Snow Grains

Precipitation of very small, white, and opaque grains of ice. Basically, this is frozen drizzle.

Snowfall

Precipitation of snow crystals that are mostly branched and in the form of six-pointed stars.

When the temperature is lower than the 0⁰ C, precipitation takes place in the form of fine flakes of snow
and is called snowfall. Moisture is released in the form of hexagonal crystals. These crystals form flakes of snow.

Ice Pellets (Sleet)

Precipitation of transparent or translucent pellets of ice, which are round or irregular hard grains of ice consisting of frozen raindrops or largely melted then refrozen snowflakes.

Sleet is frozen raindrops and refrozen melted snow-water.

When a layer of air with the temperature above freezing point overlies a subfreezing layer near the ground, precipitation takes place in the form of sleet.

Raindrops, which leave the warmer air, encounter the colder air below. As a result, they solidify and reach the ground as small pellets of ice not bigger than the raindrops from which they are formed.

Ice Crystals

Generally occurring in very cold regions, they are falling crystals of ice in the form of needles, columns, or plates.

Also called “diamond dust”, ice crystals appear like fog but with individual water particles forming directly as ice.

The shape of the individual ice crystals causes the “light pillar” optical effect above a light source.

Hailstones

Precipitation in the form of small balls or other pieces of ice falling separately or frozen together in irregular lumps.

Sometimes, drops of rain after being released by the clouds become solidified into small rounded solid pieces of ice and which reach the surface of the earth are called hailstones.

These are formed by the rainwater passing through the colder layers. Hailstones have several concentric layers of ice one over the other.

Associated with thunderstorms, individual hail stones are ¼ inch (5 mm) or greater in diameter. Hail sizes of 1 inch (2.5 cm) or more are indicative of severe thunderstorms.

Graupel (Small Hail or Snow Pellets)

Precipitation of white, opaque grains of ice that are round or sometimes conical. Diameters are less than ¼ inch (5 mm).