Mesoscale convective systems (MCS) are large regions of thunderstorms that often grow to sizes greater than 60 miles in diameter. They often form in environments where there is warm air advection taking place, coupled with a low-level southerly jet flow. These environmental conditions are often seen ahead of a trough that extends in from the west.
They often start out as scattered afternoon thunderstorms that are then able to organise due to changes in wind speed and direction with height. As the sun sets, the cooling of the cloud tops and the strengthening of the low-level jet allows these systems to become more intense and coalesce.
Other similar types of storm such as mesoscale convective complex and mesoscale convective vortex. The latter is where a small surface low pressure within the MCS pulls the winds into a circulating pattern (a vortex).
Mesoscale convective systems can last for as long as 12 hours, bringing copious amounts of rain and very frequent cloud to ground lightning but also within the clouds themselves. While they generally form in northern parts of continental Europe, they sometimes drift into Britain, typically affecting south-east England on average about once or twice a year.
