33 Development of a mesoscale convective system over the foothills of the Himalaya into a severe storm

Abstract

Abstract The occurrence of weather-related extremes has been increased considerably over low elevation plains as well as over the high altitudes in recent years. One such extreme precipitation event was recorded in Pakistan that produced 620 mm rainfall in the capital during only 10 h. Diagnostic analysis and numerical simulations have been carried out using surface and NCEP reanalysis data along with radar and satellite images for the development of a mesoscale convective system (MCS) resulting in a severe storm. It has been revealed that the sudden evolution of the MCS was the direct result of strong surface convection in moist and unstable lower layers of the atmosphere. The subsequent rapid development was the combined effect of the presence of a mid-latitude trough in the westerlies in the north and a moisture supply through monsoonal flow along the Himalaya. The westward shifting of the sub-tropical high from the north of India, and the strong divergence zone on its east edge played a significant role in developing the upward motion. Movement of the system was controlled by the steering current in the middle troposphere. The model captured the location of heavy precipitation well at 15 and 30 km resolution but failed to predict the amount of rainfall. The scale analysis shows that the MCS was the combination of α, β, and γ mesoscale systems.