cloud banner.) A cloud
plume often observed to extend downwind
from isolated, sharp, often pyramid-shaped mountain peaks, even on otherwise cloud-free days.
The Matterhorn and Mount Everest are two notable peaks where banner clouds have been frequently observed.The physics of the formation of such clouds is not completely understood. The aerodynamics
of the flow around the peak produces flow separation and dynamically induced pressure
reductions to the lee of the mountain peaks. The magnitude of the leeside pressure deficits increases with height to a maximum near the top of the peak, producing an upslope pressure gradient
and upslope flow along the lee slope of the mountain. When the air near the base of the mountain is sufficiently moist, it ascends in the upslope flow, condenses, and forms a triangular- shaped cloud, the banner cloud, to the lee of the peak. Because of its unusual shape and location, this cloud strongly resembles snow
blowing off the peak (snow banner
), and it is often difficult to tell the difference.
Copyright 2022 American Meteorological Society (AMS). For permission to reuse any portion of this work, please contact email@example.com. Any use of material in this work that is determined to be “fair use” under Section 107 of the U.S. Copyright Act (17 U.S. Code § 107) or that satisfies the conditions specified in Section 108 of the U.S.Copyright Act (17 USC § 108) does not require AMS’s permission. Republication, systematic reproduction, posting in electronic form, such as on a website or in a searchable database, or other uses of this material, except as exempted by the above statement, require written permission or a license from AMS. Additional details are provided in the AMS Copyright Policy statement.