Stratus cloud

These clouds look like flat, gray sheets.

They stay low in the sky. They can be white or dark gray. They might bring light rain or snow.

Sometimes they look like fog. These clouds form when air moves up. This makes the air cool down.

Some are thin. You can see the sun through them. Other kinds are thick. They can hide the sun.

They can stay for many days. It is a very cloudy day.

Stratus clouds are low clouds that look like flat sheets.

They can be white or dark gray. These clouds may bring light rain or small amounts of snow.

They form in a special way. Weak air currents lift a layer of air up. As the air rises, it cools down. This makes the air hold more moisture. The moisture then turns into a cloud. Some people call these clouds "high fog."

There are different types of stratus clouds. Stratus nebulosus clouds look like a smooth veil. Some are thick and block the sun. We call these opacus. Others are thin. You can see the sun or moon through them. We call these translucidus.

Another type is stratus fractus. These clouds look ragged or torn. They often form under big rain clouds. Stratus can even form from waterfalls. We call those cataractagenitus clouds. They can also form from forests. We call those silvagenitus clouds.

Stratus clouds are low-level clouds that look like flat sheets.

They often look like hazy, featureless layers in the sky. These clouds can be dark gray or nearly white. They are different from puffy clouds that grow from rising heat. Instead, they create a uniform base across the sky. These clouds may bring a light drizzle or small amounts of snow. Some people even call them "high fog" because they look so much like it.

There is a specific way these clouds form. First, weak currents of air lift a layer of air off the ground. As the air rises, it loses pressure. This causes the air to undergo adiabatic cooling, which means it gets colder as it rises. This cooling makes the relative humidity increase. This process happens when the atmosphere is very stable. The cloud can be made of water droplets or ice crystals. The type of tiny part depends on the temperature around it.

Scientists have studied many different kinds of these clouds. The name stratus comes from a prefix that means "layer." One type is called stratus nebulosus, which looks like a smooth veil. Within this group, there are two special varieties. The stratus opacus is thick enough to block the sun. However, the stratus translucidus is thinner. You can still see the sun or moon through it.

There are many other names for special stratus clouds. Stratus fractus clouds look ragged or torn. They often appear under large rain clouds like nimbostratus. Some stratus clouds come from human activity, called stratus homogenitus. Others form from the spray of waterfalls, known as stratus cataractagenitus. Even forests can help make them. These are called stratus silvagenitus because they come from evaporation in the woods.

Stratus clouds are very important for our planet. In the Arctic, they make up about 50% of the annual cloud cover. This affects how energy moves through radiation. Other clouds like stratocumulus are also very common. They cover about 23% of the Earth's oceans. These clouds reflect sunlight and help keep the Earth cool. Understanding these layers helps us predict the weather.

Stratus clouds are low-level clouds characterized by horizontal layering. They feature a uniform base that stretches across the sky. This is very different from convective or cumuliform clouds. Those other clouds form from rising thermals, or columns of warm air. In contrast, stratus clouds appear as flat, hazy, and featureless sheets. Their color can vary from dark gray to nearly white. The name comes from the prefix "strato-", which means "layer."

These clouds form through a specific atmospheric process. It begins when weak vertical currents lift a layer of air off the ground. As this air rises, it undergoes depressurization. This leads to adiabatic cooling, where the air temperature drops as it moves upward. This cooling causes the relative humidity to increase. This process typically occurs in environments where atmospheric stability is abundant. Depending on the ambient temperature, the clouds may consist of water droplets, supercooled water droplets, or ice crystals.

Scientists categorize stratus clouds into several distinct species. One species is stratus nebulosus, which looks like a featureless or nebulous veil. This species is a sign of atmospheric stability and continuous stable weather. It can produce light rain, drizzle, or snow flakes. Another species is stratus fractus, which has an irregular and ragged appearance. These are classified as pannus clouds when they appear under major rain-bearing clouds. They can also form near mountain slopes without the presence of nimbus clouds.

Within the stratus nebulosus species, there are two opacity-based varieties. The stratus opacus variety appears as a milky sheet. It is thick enough to block the sun from view. The stratus translucidus variety is much thinner. Because it is translucent, you can still observe the position of the Sun or Moon from Earth. There is also one pattern-based variety called stratus undulatus. This variety shows mild undulations and is caused by disturbances in gentle wind shear.

Stratus clouds can also be defined by their "mother clouds," or how they are born. Stratus cumulogenitus clouds occur when the base of cumulus clouds spreads out. This can also happen with nimbostratus or cumulonimbus clouds. There are even special categories for unusual origins. Stratus homogenitus are formed by human activity. Stratus cataractagenitus form from the spray of waterfalls. Finally, stratus silvagenitus are created by evaporation or evapotranspiration occurring in a forest.

These clouds play a significant role in our global environment. In Arctic regions, Arctic stratus and other low-level clouds form roughly 50% of the annual cloud cover. This has a large effect on energy emissions and absorptions through radiation. Other similar clouds, like stratocumulus, are also extremely widespread. Stratocumulus clouds cover an average of 23% of the Earth's oceans and 12% of the continents. These clouds reflect a large amount of incoming sunlight, which produces a net cooling effect on the planet.

Understanding stratus clouds helps us connect different weather systems. For example, a stratus cloud might form from stratocumulus spreading out under an inversion. This can indicate cloudy weather with drizzle for several hours. Cirrostratus clouds are another related type, but they exist at very high altitudes. They are made of ice crystals and can create halos around the Sun or Moon.

When a warm front approaches, these high cirrostratus clouds can thicken and descend to become altostratus clouds.