The dynamics of dry and wet monsoon MCS formation over West Africa: Case assessment of February 13, 2018 and June 18, 2018

Abstract

AbstractThe increasing complexity of West African mesoscale convective systems (MCSs) has signified the need for consistent studies of their evolution. Currently, most studies have focused on wet‐season MCS dynamics, but studies of dry‐season storms are equally important to enhance their predictability. Here, two severe thunderstorm case studies in the dry (February 13, 2018) and wet (June 18, 2018) seasons were probed to understand their synoptics, cloud properties, thermodynamic anomalies, and kinematic environments. Storm cloud properties were analysed using the cloud‐top temperature (CTT), cloud‐top height (CTH), cloud water path (CWP), and cloud optical thickness (COT) from the Advanced Very High Resolution Radiometer. Storm kinematics was analysed through the low‐ and mid‐level wind shear and corresponding microburst activities. Finally, the Weather Research and Forecasting model was used to simulate the vertical motion during the storms. The results showed that both storms initiated in anomalous conditions of convective available potential energy and convection inhibition, mean sea‐level pressure, and sea‐surface temperature. The development and merging of the Malian and Niger lows were pivotal in attracting moisture to feed and sustain the June storm. In addition, the formation of a surface–mid‐level moist cyclonic vortex stagnated the June storm, allowing for continual moisture uplift for storm intensification and longevity. Enhanced microburst activities on June 17 were a possible trigger of night‐time convective storm initiation, whereas strong surface to mid‐level wind shear increased storm longevity. Both storms showed high CWP, COT, CTH, and colder CTT during evolution. The synoptic mechanism for the February 13 storm differed from the midlatitudinal trough interactions with the Inter‐Tropical Discontinuity, due to an anomalous extension of the Azores High over North Africa. The dynamics of these storms enhance understanding of MCS evolution over West Africa and have implications for the region's weather forecasting.