A case of formation of convective clouds over the center-westernpart of Santa Catarina State during the morning-time was studied. Duringthe night-time of 06 Jun 2007, a large area of low top cloudiness (cumulusand stratocumulus) covering Paraná and Santa Catarina States propagatedeastward; embedded in this cloud system, over the center-western part ofSanta Catarina State, the onset of convective clouds took place during themorning-time of 07 Jun 2007. Later on, the convective cloud systemenhanced, propagated eastward, interacted with other diurnal convectiveclouds, weakened during night-time and dissipated up shortly before themorning-time of 08 Jun 2007. Simulations using the MM5 regional modelwith horizontal grid spacing of 12 km showed that Serra do Mar acted asbarrier to the low level northwesterly flow from Mato Grosso do Sul,bringing about atmospheric convergence at the western side of Serra doMar; associated with this convergence, the presence of low level jets (LLJ)or a maximum velocity core (MVC), like those observed over Porto AlegreCity during the case and simulated by MM5, would explain the formationof convective clouds. This mechanism would lead to convection formationand depended strongly on the generation of LLJ/MVC at the lowest levelsof the atmosphere, i.e., the influence of the vertical wind shear, the verticalstratification and the vertical decoupling that exists within the nocturnalboundary layer.
