Airflow through a developing midlatitude disturbance is analyzed in a relative-wind isentropic system in order to provide insight into how the cloud pattern evolves into the familiar comma shape. The model presented makes use of various concepts such as that of the conveyor belt and explores the relationship between the configuration of the major airstreams and such features as the jet streams and the dry tongue. The model also relates vertical motion and precipitation to the origin and vertical displacement of the airstreams and attaches special significance to airstream boundaries, which manifest themselves as sharp discontinuities in cloud and weather patterns.

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