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Forms of Precipitation

What is Precipitation?

The definition of precipitation is any form of water – liquid or solid – falling from the sky. It includes rain, sleet, snow, hail and drizzle plus a few less common occurrences such as ice pellets, diamond dust and freezing rain.


What is rain?

In order for the raindrops to become heavy enough to fall, droplets of water in the cloud collide together with other droplets and other particles in the air – like soot and dust – to become larger. Once the drops become too heavy to stay in the cloud, they start falling, resulting in rain. There are three main types of rainfall – frontal rain, orographic rain and convective rain.
Raindrops can be up to 6 mm in diameter, but anything less than 0.5 mm in diameter is classed as drizzle.

What is drizzle?

Drizzle consists of very small droplets of water falling from low-level stratus clouds.
Drizzle droplets are less than 0.5 mm in diameter.

What is freezing rain?

Freezing rain is rain droplets which fall in supercooled liquid form, but freeze on impact with the ground or another object to form clear ice – also known as glaze. Supercooling occurs in clouds where droplets remain in a liquid from in temperatures below the normal freezing point. In order for the supercooled droplets to freeze on impact, the ground temperature is normally close to or below 0 °C.

What is hail?

Hail is solid precipitation in the form of balls or pieces of ice known as hailstones. Hail only
forms in Cumulnimbus more commonly known as thunder clouds.
Hailstones can vary in size from 5 mm to 150 mm in diameter, however most hailstones are smaller than 25mm.

What are ice pellets?

Ice pellets are snowflakes which have started to melt, and then re-frozen as they fall through colder air. The result is a grainy snow pellet encased in ice. Ice pellets are generally smaller than hailstones and bounce when they hit the ground.

What is snow?

Snow is tiny ice crystals stuck together to become snowflakes. If enough ice crystals stick together,
they’ll become heavy enough to fall to the ground.

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