Stratus clouds are low-level layers with a fairly uniform grey or white colour. Often the scene of dull, overcast days in its 'nebulosus' form, they can persist for long periods of time. They are the lowest lying cloud type and sometimes appear at the surface in the form of mist or fog.
Stratus clouds form in calm, stable conditions when gentle breezes raise cool, moist air over colder land or ocean surfaces. These clouds can exist in a variety of thicknesses and are sometimes opaque enough to darken days allowing for little light to pass through.
Stratus are usually accompanied by little to no rainfall, however if they are thick enough they can produce light drizzle. This drizzle can also fall in the form of light snow if cold enough.
Due to the nature of stratus it only has two defined species:
· Stratus nebulosus - This is a featureless, dark layer which is capable of producing drizzle.
· Stratus fractus - This is a stratus layer which is starting to break up or 'dissipate', leading to breaks in the cloud.