Thunderstorm Activity over Delhi during Summer 2025: Part I–Observational and Thermodynamic Characteristics

It is challenging to predict thunderstorms (TS), gusty winds, and related phenomena during the pre-monsoon season (March–May) and even in June over Delhi and its vicinity. Predicting the intensity in terms of wind speed, location, and timings of occurrence in short- to medium-range forecasts is difficult. The best tool to monitor and forecast thunder-related hazards is the nowcast. In the nowcast scale, we can predict a few hours before severe TS occur over the region. This paper studies the nine severe TS cases that occurred during the pre-monsoon/summer months of 2025 (11th April, 01–02nd May, 11th May, 13th May, 17th May, 21st May, 24th May, 31st May, and 1st June) and their observational and thermodynamic aspects. The observational aspects showed that the average duration of severe thunderstorms was 79 minutes, with the fastest ending TS event being 15 minutes on 21st & 31st May, and the longest TS event occurring on 11th May (215 minutes). The strongest winds of 50.8 knots were reported over Palam on 1st June, followed by 45 knots on 11th April over UJWA. The frequency of TS occurrences was highest in May (12 cases), followed by April (3 cases), and least in March (2 cases), with above normal TS days in May 2025. Out of nine severe TS events, Delhi had the highest frequency (66.7%) of medium time duration (30–90 minutes), followed by short duration (<30 minutes) (22.2%), about 67% TS events occurred in the afternoon/evening. The mean/threshold values of the thermodynamic parameters, Convective Available Potential Energy (CAPE), Convective Inhibition (CIN), Lifted Index (LI), Showalter Index (SHOW), Severe Weather Threat (SWEAT) Index, K Index (KI), Total Totals Index (TTI), Equilibrium Level (EQL), Level of Free Convection (LFC), Bulk Richardson Number (BRN), and Total Precipitable Water (TPW) were 1025.25 J/kg, –243.294 J/kg, –3.395 °C, –2.466 °C, 259.413, 32.812 °C, 51.317 °C, 334.688 hPa, 636.063 hPa, 35.719, and 37.969 mm, respectively.The frequency analysis of normalized thermodynamic indices showed that the best predictors for TS activity over Delhi region would be LFC, KI and CIN. These results will update the existing literature in the field, being the most recent study based on recent season of 2025, this may be applied in operational weather forecasting and nowcasting.