banner cloud

(meteorology) A cloud plume often observed to extend downwind from isolated mountain peaks, even on otherwise cloud-free days. Also known as cloud banner.

A cloud developing to one side of a peak, elongated by the prevailing wind; the Matterhorn is often adorned with a banner cloud. As air rises over mountain barriers, condensation may occur, and where the mountain is high enough for air not to rise entirely above it, banner clouds may form.