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A nimbostratus cloud is a multilevel, amorphous, nearly uniform, and often dark-grey cloud that usually produces continuous rain, snow, or sleet, but lightning or thunder. Although it is usually a low-based cloud, it actually forms most commonly in the middle level of the troposphere and then spreads vertically into the low and high levels. Nimbostratus usually produces precipitation over a wide area. The prefix nimbo- comes from the Latin word nimbus, which denotes "cloud" or "halo". Downward-growing nimbostratus can have the same vertical extent as most large upward-growing cumulus, but its horizontal expanse tends to be even greater.