A stream of cold air that flows westwards approximately parallel to, and ahead of, a warm front in a depression, below the encroaching warm air. It generally rises away from the surface to the middle levels near the tip of the warm sector, where it encounters the air mass behind the cold front. It then tends to split with the poleward flow creating the distinctive cloud head of the depression. The other, equatorward flow causes a descent of cold, dry air from the upper troposphere and lower stratosphere, producing the dry intrusion behind the cold front. See also split front; warm conveyor belt.
Subjects: Meteorology and Climatology.