The passage of a cold front is a common occurrence in the UK, often bringing a spell of wind and rain, with colder air following behind. Along the frontal boundary, warm air residing ahead of the front is forced to rise above the colder, denser incoming air. This is a form of convection, a process generating lively rainfall at the surface.
Along stronger cold fronts, where temperature differences either side are larger, convection is stronger, generating heavier rainfall. This rain can organise into narrow bands stretching along the frontal boundary, appearing on weather radar as lines of intense rainfall – this is “line convection”. These features can bring a brief spell of torrential rainfall and squally winds that are often no more than 3 miles (5km) wide.
Line convection is often broken up into strong line segments, which are discrete lines of intense precipitation and strong winds separated by calmer gaps. As a line segment passes overhead, temperatures can quickly drop, pressure can jump up and the wind can veer abruptly.
In rare cases, tornadoes can form from complex wind patterns between line segments. One such case occurred in the village of Humberston in north-east Lincolnshire on 27 September 2021, causing damage to homes and vehicles.
