Terrain Induced (Orographic) Feeder Clouds


As defined in the AMS Glossary of Meteorology, a feeder cloud is part of the "seeder–feeder orographic precipitation-enhancement mechanism, in which precipitation from an upper-level precipitating cloud (seeder) falls through a lower-level orographic stratus cloud (feeder) capping a hill or small mountain." Feeder clouds form when air cools and saturates as it rises up higher terrain. The clouds provide an added source of water droplets from which ice crystals falling from higher clouds can feed off of to grow larger.

In Duluth a scaled down or "poor man's version" of this process may occur, along with some help from Lake Superior. Even when conditions are not favorable for lake-effect snow, low clouds still frequently form over the lake. The clouds develop further as onshore winds push them up the steep hill in Duluth. Depending upon factors, including the stability of the air and the amount of cloud formation upstream over the lake, light drizzly precipitation can form. This author has seen days where light precipitation was occurring along and inland of the ridge crest but not at the bottom of the hill. Ice crystals falling into the clouds have a little more moisture to grow from than if the hill was not there.


More information on feeder clouds:

Seeder-Feeder Mechanism in AMS Glossary of Meteorology.