All cloud types
“Heavy gray data cloud blocking all light”
Formation
Widespread gentle lifting of moist air
Weather signal
Steady rain or snow
Technical specs
Altitude2,000-18,000 ft
AppearanceDark, thick, uniform gray layer
Fun factThe quintessential 'rain cloud'. Dark enough to require streetlights.
common
Etymology
Latin: 'nimbus' (rain storm) + 'stratus' (layer)