The panorama above showing an attention-getting mackerel sky was taken from Hertfordshire , England on August 3, 2014. This high dynamic range (HDR) image is composed of 15 separate photos. Said to resemble the scales of a mackerel , this type of sky has long been used by sailors as an indicator of the coming weather: Mackerel sky, mackerel sky - never long wet, never long dry. Both altocumulus and cirrocumulus clouds can give a scaly or buttermilk appearance to the sky.