Definition
A thick, dark, low-to-middle level cloud layer that produces continuous, steady precipitation in the form of rain, snow, or ice pellets. Nimbostratus clouds form a featureless gray sheet that blocks the sun, often extending across a wide horizontal area and through several thousand feet of vertical depth. They are associated with stable air and warm fronts.
Plain English
A wide, gray, rain-producing cloud layer that brings steady (not stormy) precipitation and blocks out the sun for hours at a time.
Context Anchor
Seen in cloud identification, weather reports, and preflight weather planning when a pilot is checking for widespread rain, snow, low cloud bases, or reduced visibility.
Derivation
From Latin nimbus meaning "rain cloud" and stratus meaning "spread out" or "layered." The combination literally describes a layered rain cloud, which matches what pilots see: a flat, spread-out sheet that produces steady rain.
Why Pilots Care
Signals continuous precipitation that can lead to reduced visibility, icing risks, and the need to alter flight plans.
Grounding Statement
Picture a wide, dark-gray blanket of cloud covering the sky and producing steady rain or snow rather than brief showers.
Intuition Check
Do not think of nimbostratus as a tall thunderstorm cloud. It is mainly a broad layered cloud that brings steady precipitation over a wide area.
Example Sentence 1
The briefer warned of a nimbostratus layer along the route, with steady rain and ceilings around 1,500 feet for most of the morning.
Example Sentence 2
Nimbostratus layers often extend over hundreds of miles, creating widespread instrument conditions.