low pressure system that is completely encircled by an isobar. They often move slowly, as they displaced south of the main westerlies. Although, strictly speaking, all lows are closed, this term distinguishes a low from a trough on a surface chart, and on upper level charts, it accentuates that the circulation is "closed." A form of cut-off low.
A low pressure system that may be completely encircled by an isobar or contour line. Strictly, all lows are "closed". But in weather analysis terminology, this is used to distinguish a low from a trough and on upper level charts to accentuate that fact that the circulation is closed and at latitudes and levels where such an occurrence is unusual.
A region of low pressure distinguished by a center of counterclockwise circulation (in the Northern Hemisphere), and is surrounded by one or more isobars or height contours. Closed lows aloft (i.e., above the surface) may become disconnected from the primary westerly flow and thus progress eastward more slowly. It is important to note that a cutoff low is a closed low, but not all closed lows are cutoff lows.