Decoding the dynamics: Interaction of Western disturbances and Easterly troughs driving extreme weather over India

Abstract

Western Disturbances (WDs) are critical mid-latitude weather systems that influence winter precipitation across northern India. Their interaction with easterly troughs, however, remains less understood, particularly during extreme weather events. This study examines a rare and high-impact synoptic interaction between a WD and an easterly trough during 26-29 December 2024, which resulted in record-breaking rainfall over Delhi and widespread severe weather across northwest and central India. Using multi-source datasets including synoptic charts, satellite imagery, lightning data, and moisture diagnostics (MIMIC-TPW2 and ERA5-derived VIMDF), we decode the dynamic and thermodynamic processes underpinning this event. Our analysis highlights the sequential intensification and eastward progression of the WD and its induced cyclonic circulations, supported by active subtropical jet stream dynamics and strong upper-level divergence. The coupling with an easterly trough led to enhanced low-level convergence and deep convection. Lightning activity and moisture transport patterns confirmed the role of both Arabian Sea and Bay of Bengal sources in fueling the precipitation. The study underscores the significance of synoptic-scale interactions in driving extreme weather and advocates for improved monitoring of such coupled systems to enhance forecasting accuracy. These findings have implications for disaster preparedness and weather prediction over the Indian subcontinent.