What word or phrase does your mother always say?
Plural nimbostrati (nĭm'bō-strāt'ī')
A dark, gray, mid-altitude cloud that often covers the entire sky and precipitates rain, snow, or sleet. Nimbostratus clouds generally form around 2,000 m (6,560 ft) but often extend to much higher and lower altitudes. See illustration at cloud.