Lower level clouds lie at an altitudes of 2,000 m or lower. They are mostly composed of water droplets. However, when temperatures are cold enough, these clouds may also contain ice particles and snow. Stratus, cumulus, Cumulonimbus and stratocumulus clouds are lower level clouds.
Stratus clouds are composed of thin layers or patches of clouds with fuzzy edges, covering a large area of the sky. Sometimes they appear at the ground level in the form of mist or fog.
They can be easily distinguished in the sky by their long horizontal layers with foggy appearance. Stratus clouds are a fairly uniform grey or white in colour, however they can exist in a variety of thicknesses and are sometimes opaque enough to darken the days. Stratus clouds form in calm, stable conditions when gentle breezes raise cool, moist air over colder land or ocean surfaces. They are usually associated with little to no rainfall. However, if they are thick enough, they can produce light drizzle or even light snow, if the temperature is cold enough. Stratus clouds are very common all over the world most especially in the coastal and mountainous regions.
Cumulus clouds, shaped like detached cauliflowers, are one of the most common and distinctive types of cloud. They can range in size from resembling balls of cotton to big heaps of mashed potatoes in the sky, which explains the name ‘cumulus’ which is Latin for ‘heap’.
The top of these fluffy clouds is mostly brilliant white when lit by the sun, although their base is usually relatively dark. Cumulus clouds are often referred to as “Fair weather clouds,” because they are usually a sign of fair weather and are not associated with precipitation. But, if they get bigger, they can sometimes discharge light showers. Cumulus clouds develop due to convection. As the air at the surface becomes hot, it is lifted, it cools and water vapour condenses to produce the cloud. Throughout the course of the day, if conditions allow, these clouds can grow in height and size and can eventually form into cumulonimbus clouds.
Cumulonimbus clouds, otherwise known as the ‘King of Clouds', exist through the entire height of the troposphere. They are fluffy and white like cumulus but their formations are far larger. It is a vertical developing type of cloud, whose base grows from one to up to eight km, and hence it is also called a ‘tower cloud’.
Cumulonimbus clouds are, in fact, characterised by their icy, anvil-shaped top. They are heavy and dense, menacing looking, and low-level clouds. Commonly known as’ thunderclouds’, they are associated with extreme weather, such as heavy torrential downpours, hailstorms, lightning and even tornados. Only cumulonimbus clouds can produce thunder, hail and lightning. Cumulonimbus clouds are formed due to convection, often growing from small cumulus clouds over a hot surface. They can also form along cold fronts as a result of forced convection, where milder air is forced to rise over the incoming cold air.
Stratocumulus clouds are large, dark, rounded masses of stratus, that usually form groups, lines or waves. They are low level patches of cloud, varying in colour, from bright white to dark grey. They have well defined bases and some parts are much darker than others. From dry settled weather to light rain and snow, stratocumulus clouds can be present in all types of weather conditions. Stratocumulus clouds usually form from breaking up a layer of stratus cloud. They are indicators of a change in the weather and are usually present near a warm, cold or occluded front. Often they are mistaken for rain clouds, when in reality it is quite rare to get anything more than the lightest drizzle from them.
Cumulus and Cumulonimbus clouds are clouds of great vertical development. Rather than spreading across the sky, these clouds grow high up into the atmosphere and often spread out on top in the form of an anvil. Clouds with vertical growth are evidence of strong vertical convection currents and apart from torrential rain, accompanied with vivid lightning and thunder, cumulonimbus clouds also occasionally bring hails and more rarely, a tornado.