Rising air expands and cools (adiabatic cooling: that is, it cools due to change in volume as opposed to adding or taking away of heat). The result is condensation/precipitation. Cold air sinks. Sinking air compresses and heats.

Rising air always cools, and, conversely, sinking air always warms. This type of temperature change, which is caused simply by ascent or descent in the atmosphere, is called adiabatic cooling or warming. When air moves vertically, its pressure changes.

All fronts slope in the vertical so that the warmer (less dense) air mass sits on top of the colder (more dense) air mass. In other words, the warmer air mass is forced to rise over the colder air mass. As air from the warm air mass rises, it cools, leading to the development of clouds and maybe precipitation.

A rising parcel of air expands because the air pressure falls with elevation. This expansion causes the air to cool.

Well, high pressure is associated with sinking air, and low pressure is associated with rising air. The opposite occurs with high pressure. Air is moving away from the high pressure center at the surface (or “diverging”) so as a result, air from above must sink to take its place.

As a parcel of air in the earth’s atmosphere rises through the atmosphere, it experiences decreasing pressure and thus expands. This expansion lowers the temperature of the air parcel, and therefore the air cools as it rises.

Why does a rising air parcel cool off? It expands. You just studied 45 terms!

Evaporation and transpiration change liquid water into vapor, which ascends into the atmosphere due to rising air currents. About 90 percent of water in the atmosphere is produced by evaporation from water bodies, while the other 10 percent comes from transpiration from plants. There is always water in the atmosphere.

This allows the parcel of air to rise until all of the ‘surplus’ water vapor has condensed and all the latent heat has been released. Therefore, the main reason which stops clouds growing upwards is the end of the release of latent heat through the condensation process.

Precipitation forms in the clouds when water vapor condenses into bigger and bigger droplets of water. When the drops are heavy enough, they fall to the Earth. If a cloud is colder, like it would be at higher altitudes, the water droplets may freeze to form ice. Most rain actually begins as snow high in the clouds.

Light rain — when the precipitation rate is < 2.5 mm (0.098 in) per hour. Moderate rain — when the precipitation rate is between 2.5 mm (0.098 in) – 7.6 mm (0.30 in) or 10 mm (0.39 in) per hour. Heavy rain — when the precipitation rate is > 7.6 mm (0.30 in) per hour, or between 10 mm (0.39 in) and 50 mm (2.0 in) per …

Solution: 1) The air must contain water vapor that can precipitate, 2) the moist air must cool down in order to release water in liquid form, and 3) there must be condensation nuclei for water vapor to condensate on.

Clouds that produce rain and snow fall into this category. (“Nimbus” comes from the Latin word for “rain.”) Two examples are the nimbostratus or cumulonimbus clouds. These low-level clouds are full of moisture. Cumulonimbus clouds are also called thunderheads.

Hailstones are usually the size of small rocks, but they can get as large as 15 centimeters (6 inches) across and weigh more than a pound. Snow is precipitation that falls in the form of ice crystals. Hail is also ice, but hailstones are just collections of frozen water droplets. Snow has a complex structure.