The usual development of CAD is when a cool high-pressure area wedges in east of the Appalachians, a persistent cloud deck with associated precipitation linger across the region for prolonged periods of time.
The usual development of CAD is when a cool high-pressure area wedges in east of a north-south oriented mountain chain. As a system approaches from the west, a persistent cloud deck with associated precipitation forms and lingers across the region for prolonged periods of time.