Rain: Most commonly observed, 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.
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.
Hail: Precipitation in the form of small balls or other pieces of ice falling separately or frozen together in irregular lumps. 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.
Small Hail (Snow Pellets): Precipitation of white, opaque grains of ice that are round or sometimes conical. Diameters are less than ¼ inch (5 mm).
Snow: Precipitation of snow crystals that are mostly branched and in the form of six-pointed stars.
Snow Grains: Precipitation of very small, white, and opaque grains of ice. Basically, this is frozen drizzle.
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 with individual water particles forming directly as ice. The shape of the individual ice crystals causes the 'light pillar' optical effect above the light source.
Rain: Rain is the most familiar form of precipitation. It occurs when liquid water droplets in the atmosphere combine and fall to the ground. Raindrops have a diameter of at least 0.5 millimeters.
Snow: Snow occurs when water vapor in the atmosphere freezes into ice crystals without melting into liquid first. These ice crystals then combine to form snowflakes. Snowflakes can vary in size and shape, and they fall to the ground as individual flakes.
Sleet: Sleet consists of small ice pellets or frozen raindrops. It forms when raindrops fall through a layer of freezing air near the Earth's surface, causing them to freeze before reaching the ground. Sleet can bounce when it hits a surface.
Freezing rain: Freezing rain is similar to sleet but differs in that raindrops do not freeze completely. Instead, they become supercooled upon contact with a cold surface, forming a layer of ice. Freezing rain can create hazardous conditions, as it can coat surfaces such as roads and power lines with ice.