What does altostratus mean?
Altostratus is a noun used chiefly in meteorology to describe a mid-level cloud that appears as a smooth, grey or bluish-grey sheet covering large areas of the sky. Formed of water droplets and ice crystals at heights of roughly two to seven kilometres, it is typically dense enough to hide the sun's outline yet thin enough in places for the sun to appear as a watery, blurred disc — a phenomenon sometimes called a 'watery sun'. Altostratus frequently signals the approach of a warm front and often precedes steady, prolonged rain or snow. The word derives from the Latin stratus, meaning 'spread out' or 'layered', combined with the prefix alto-, denoting height, and belongs to the family of cloud names codified in the nineteenth century by Luke Howard. While most familiar from forecasts and aviation reports, altostratus also enriches descriptive writing about weather and landscape.
nounA layer of grey or bluish cloud composed of water droplets and ice crystals, occurring at mid-level altitudes (roughly 2,000–7,000 metres) and often thin enough for the sun to be faintly visible through it.
- A mid-level, sheet-like cloud of grey or bluish appearance that often covers the whole sky and may precede a warm front and precipitation.
"A sheet of altostratus dimmed the afternoon sun, promising rain by evening."
"By mid-morning the altostratus had thickened into a uniform grey veil across the sky."
"Pilots reported a solid altostratus deck between six and ten thousand feet along their route."
Rarely used; altostratus is almost always treated as a singular mass noun even when referring to extensive cloud cover.
"Several distinct altostrati were visible at different levels during the frontal passage."
Altostratus was named in the early 1800s by an amateur meteorologist whose Latin cloud names are still used by every weather forecaster on Earth.
Reviewed by Deb Chak, Editor. AI-assisted content curated by RJS Tech Solutions LLP.
Etymology of altostratus
The word altostratus combines the prefix alto- (from Latin altus, 'high') with stratus, Luke Howard's 1803 coinage from the Latin for 'spread out' or 'layered'. Howard, an amateur meteorologist, devised the Latin cloud classification system on which all modern cloud nomenclature rests. The compound form arose in the nineteenth century as meteorologists subdivided Howard's original genera by altitude, giving rise to parallel terms such as altocumulus and cirrostratus.
How altostratus is actually used
Altostratus is primarily a technical term used in meteorology, aviation, and weather reporting, though it appears in general contexts such as weather forecasts and nature writing. It is always treated as a mass noun describing cloud type rather than countable individual clouds. The plural form is rare outside specialist literature.
Easily confused with altostratus
Altocumulus forms puffy, patchy clumps at similar mid-level altitudes, whereas altostratus is a smooth, featureless sheet.
Stratus is a low, fog-like cloud near the ground, while altostratus occurs much higher in the middle of the troposphere.