1. A thin, uniform layer of gray or blue-gray cloud that often covers the entire sky, typically occurring at middle altitudes (6,500–20,000 feet).
Usage: meteorology; usually uncountable

Examples

• The altostratus clouds dimmed the sunlight but did not block it completely.
• Meteorologists identified the altostratus layer as a sign of approaching warm, moist air.
• On overcast days, altostratus often forms a featureless gray blanket across the sky.
• The sun was visible as a pale disk through the thin altostratus clouds.
• Altostratus clouds typically indicate that rain or snow may fall within the next 12 hours.