altostratus
noun [ U ] environment specialized uk/ˌæl.təʊˈstrɑː.təs/ us/ˌæl.toʊˈstreɪ.t̬əs/
层云（灰白成层的云雾，见于中等高度）
a type of stratus (= a flat, grey cloud) formed in thin layers and found at medium height, above the level of stratus
Compare: cirrostratusnimbostratus