On the WeatherRadar there was a narrow, darker line of rain within the wider band. This is known as a squall line, but do you know what it indicates?

A squall line is a narrow, linear band of thunderstorms, as seen on the WeatherRadar, that produce particularly heavy and intense downpours. Though narrow, they can extend over hundreds of kilometres long.

It can often be associated with hail, frequent lightning strikes and gusty winds as it passes through, which is often at quite a rapid speed, although they can still last several hours.

Squall lines most commonly form along or ahead of cold fronts, in highly unstable environments. As the cold air advances, it forces warmer, moist air in its path to rise, condense and form clouds, with continuous updrafts along its leading edge encouraging growth.

They tend to begin as a narrow band of convective cumulonimbus clouds, evolving into a broader system over time, thriving in conditions of strong updrafts, strong vertical wind shear, and strong low-level winds.

If a squall line forms in arid regions, this can result in a haboob, as explained here.