Cirrostratus nebulosus (Cs neb), the uniform cirrostratus veil, is completely smooth, featureless and milky in appearance, partially or completely covering the sky. The most striking feature is that almost every Cs nebulosus exhibits a whole range of halo phenomena. The haloes and other optical phenomena are most marked when the uniform single cloud layer is thin and gradually disappear as it thickens indicating an approaching active disturbance.
