Pacific Daylight Time (PDT) is a time zone that is 7 hours behind Coordinated Universal Time (UTC-7). It is observed in parts of the western United States and Canada during the summer months when clocks are set forward by one hour to make better use of daylight. PDT typically begins on the second Sunday in March and ends on the first Sunday in November. During this period, regions that observe PDT include major cities like Los Angeles, San Francisco, and Vancouver. When PDT ends, these areas revert to Pacific Standard Time (PST), which is UTC-8.