trowal A Canadian meteorological term for the line of the upper front of an occlusion and the region about it where the warm air, having been lifted off the surface, is still relatively low. It is a trough or valley of warm air that is still undergoing lifting, and is normally marked by clouds and precipitation.

What is a purple front?

After the front passes, the sky is usually clearer, and the air is drier. On a weather map, shown to the left, an occluded front looks like a purple line with alternating triangles and semicircles pointing in the direction that the front is moving.

What is the difference between a trough and a front?

A trough is an elongated area of lower air pressure. Since pressure is closely linked to wind, there are often changes in wind direction across a trough. … However such a weather front is usually less convective than a trough in the tropics or subtropics (such as a tropical wave).