Extreme storms create significant hazards over Lake Victoria and the surrounding area, and a better understanding of their formation and development is still needed. Here, 50 of the most intense simulated rainfall events over the lake produced from convection-permitting WRF model simulations are analyzed to identify the environmental conditions and physical processes underlying storm development. Each storm examined is preconditioned by an anomalous accumulation of atmospheric moisture over the lake, beginning at least 18 h prior to the event. Larger storms are associated with greater precursory moisture accumulations. The synoptic-scale environment plays a pivotal role in enhancing moisture availability and atmospheric convergence over the lake. Changes in mid-level 700–500 hPa circulation yield an earlier nighttime transition from divergence to convergence in the meso-scale lake/land circulation, enhancing moisture accumulation within the highly convergent environment and extending the duration of favorable conditions for intense precipitation to develop. In addition, mesoscale outflow boundaries from surrounding land-based convection shapes nocturnal offshore flows, localizing convergence zones and influencing the spatial distribution of extreme rainfall over the lake. A subset of seven storms exhibits capping inversions that persist longer into the night compared to the other extreme storms, delaying convective initiation but allowing for greater build-up of CAPE and instability prior to storm genesis over the lake. These storms, while more spatially localized, exhibit rainfall intensities comparable to the other extreme storms. Our results underscore the important interactions between synoptic conditions, mesoscale dynamics, and thermodynamic instability in modulating extreme storm formation over Lake Victoria.
Vizy et al. (Thu,) studied this question.