Nimbostratus is an extensive grey layer associated with persistent rain or snow, usually reaching the ground. Its thickness hides the Sun, and lower ragged clouds can hang beneath it. Those fragments are not necessarily the main precipitation-bearing layer.
This type earns a place because an overcast sky is not one uniform category. Compare the broad background with the torn foreground clouds in the photograph. Record precipitation and the overall layer, rather than naming every dark scrap nimbostratus. Darkness alone is not enough for identification.
Photo: GerritR · CC BY-SA 4.0. Resized and recompressed; image retains its source license.
