Stratus clouds are clouds that form in flat layers. Recall that strato means "spread out." Stratus clouds usually cover all or most of the sky and are a uniform dull, gray color.
As stratus clouds thicken, they may produce drizzle, rain, or snow. They are then called nimbostratus clouds.
Clouds names are based off of their height. Clouds that form between 2 and 6 kilometers have the prefix alto-, which means "high." Altostratus is a "middle-level" cloud that is higher than a regular stratus cloud but lower than cirrus and other "high" clouds.
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