Stratus clouds are essentially ground-level fog that blankets the sky in uniform grey.

Nature · Published 3 October 2026 Swipe more like this →

In short: Often dismissed as the culprit behind dull, overcast days, stratus clouds are the lowest-lying clouds in our atmosphere. These featureless, layered sheets form in calm conditions when moist air rises gently. While they rarely produce heavy weather, they can persist for days, sometimes appearing as mist at the surface.

Stratus clouds occupy the lowest tier of the atmosphere, with bases typically found between the surface and 1,200 feet, though they can extend up to 6,500 feet. Derived from the Latin word for 'flattened' or 'spread out,' these clouds are defined by their uniform, horizontal layering. Unlike convective clouds that grow vertically through rising thermals, stratus clouds form in stable environments where gentle breezes lift cool, moist air over colder land or ocean surfaces.

Because they lack the dramatic structure of cumulonimbus or the cauliflower-like appearance of cumulus, stratus clouds are often described as featureless. They are categorized into two primary species: 'nebulosus,' which presents as a dark, uniform veil, and 'fractus,' which appears as ragged, dissipating fragments. While they are generally associated with dry, stable weather, they can occasionally produce light drizzle or, if temperatures are sufficiently low, light snow. In some cases, they are opaque enough to significantly dim the daylight.

The persistence of these clouds is notable; they can linger for extended periods, particularly in anticyclonic conditions. Their presence is not merely a local phenomenon. Research by Sednev, Menon, and McFarquhar highlights that stratus and other low-level clouds constitute approximately 50% of the annual cloud cover in Arctic regions. This prevalence makes them a critical factor in regulating energy emissions and absorption through radiation, demonstrating that these seemingly mundane, grey blankets play a vital role in the global climate system.

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