Normally, when we think of clouds we picture fluffs that look like cottonballs or well-feed sheep. Stratus clouds are not in that category at all. Stratus clouds (St) are typically classified as Family C, aka Low-level clouds with little vertical development. They are flat and featureless, with a color ranging from pale shroud white to nicotine gray. They are smooth and formless, like ghosts.
They are usually the culprits behind a weatherman's forecast of "cloudy" -- sometimes with a chance of drizzle. Stratus clouds are skilled at blocking the sun and can dampen anyone's enthusiam for sunbathing. Stratus clouds are basically layers of fog that has climbed in altitude either by the virtue of a morning pick-me up or clamboring above a wash of cold air.
The base of stratus clouds is generally below 6,000 feet (2,000 m). They are quite uniform in appearance and lack any type of ambition to develop into a proper storm. The worst they have ever done to rain on someone's parade is dust a sprinkling of snow. But they are hazardous to Visual Flight Rule (VFR) pilots because of widespread decreased visibility, and have been behind several notable cases of vestibular disorientation. Pilots can easily become confused when the normal cues for up and down are difficult to see, and may develop vertigo. Or they may miss another plane flying at the same altitude altogether. Anything that results in reduced visibility can be dangerous, so stratus makes the list for in-flight hazards.
Here is their family photo album: