Dynamical and thermodynamic mechanisms driving the April 2025 severe thunderstorm over eastern India

On 10 April 2025, a severe thunderstorm impacted eastern India, causing disastrous impacts across 19 of Bihar's 38 districts. Survey-estimated peak surface winds of 120 km/h (based on structural damage assessment) contributed to 63 deaths—40 from wind-related hazards and 23 from lightning strikes—with the district of Nalanda experiencing the most extensive devastation. This study presents an observational and diagnostic examination of the storm using ERA5 reanalysis, INSAT-3DR satellite data, Radiosonde/Radio Wind (RS/RW) Patna profiles, Automatic Weather Station (AWS) surface observations, Indian Lightning Location Network (ILLN) data, and district-level rainfall and impact statistics. The pre-storm environment showed marked convective instability across the Gangetic Plain, with surface-based CAPE (SBCAPE) reaching values favourable for organized deep convection, corroborated by mixed-layer CAPE (MLCAPE) and most-unstable CAPE (MUCAPE). A pronounced south–north moisture gradient was associated with differential surface heating, boundary-layer destabilization, and elevated thermodynamic instability. Mid-tropospheric cold-air advection steepened environmental lapse rates, while deep-layer wind shear appeared to influence storm motion and organization. Two convective cells, initiated independently over north-central Uttar Pradesh (~ 0300 UTC) and northern Chhattisgarh–Jharkhand (~ 0700 UTC), merged over central Bihar around 0915 UTC into a mesoscale convective system exhibiting organizational features similar to the bow-echo morphology. This merged system was associated with the most intense surface winds and lightning activity, peaking between 1000 and 1100 UTC, before dissipating from around 1100 UTC as thermodynamic support declined and the system moved eastward. These findings suggest the importance of several dynamical and thermodynamic precursors to severe convective events over the eastern Gangetic Plain and emphasize the necessity of improved impact-based early-warning systems for localized thunderstorm hazards in eastern India.