Unique observations of a back-building MCS in the arid Kalahari region of South Africa

During a first-of-its kind observational field campaign in the Kalahari region of South Africa, the Kalahari Atmospheric Processes Experiment (KAPEX), aimed to collect data of the Kalahari heat low which develops there during the early and peak austral summer months (www.kapex24.com) . Due to the high frequency of drylines during December months, KAPEX provided a unique opportunity to monitor the environment in which drylines and dryline-related convection occur in the region. On 28 December 2023, a dryline was positioned approximately 200km west of the observation site. A thunderstorm which developed in close proximity to the dryline merged with other storms nearby, forming a mesoscale convective system (MCS) that resulted in localised flooding and power outages in the region. New cells continued to develop along the dryline, where low-level convergence was enhanced by the storm’s outflow, before being transported downstream by strong mid-level northwesterlies. Satellite and lightning data are utilised to analyse the storm’s development and motion, while surface observations of weather stations erected for the duration of the campaign, together with 4-hourly upper air ascents, allow a detailed analysis of the storm’s formation environment and impact in a region with no radar coverage and sparse surface observations. These observations are complimented by a 4km Unified Model simulation which assists in identifying mesoscale features such as the cold pool and outflow boundaries.