What is a TROWAL?
The trowal is part of the warm conveyor belt (WCB) that turns cyclonically (counterclockwise) into the low pressure system, unlike the original observation noted by Carlson (1980) in which the WCB turned anticyclonically (clockwise) in mid-to upper-levels.
In essence, the trowal is a wedge of warm air aloft displaced poleward of the surface warm occluded front.
The trowal marks the three-dimensional sloping intersection of the upper cold frontal portion of the warm occlusion with the warm frontal zone (Martin 1998; 1999).
Martin (1999) showed a conceptual model of the trowal associated with a surface warm occlusion where the precipitation falls with respect to the position of the trowal.