Physical mechanisms distinguishing severe-weather-producing and non–severe-weather-producing precipitation in Northern Thailand's pre-monsoon environment

Abstract

Severe pre-monsoon convection in northern Thailand frequently produces damaging winds and hail, yet the physical mechanisms that distinguish severe-weather-producing environments from ordinary rainfall remain poorly understood. This study analyzes 222 pre-monsoon days (2015–2024) across nine provinces using 00 UTC radiosonde soundings and ERA5 synoptic composites to identify the atmospheric controls that separate Severe-Weather-Producing Events (SWPE) from non-severe counterparts (NSWPE). Among 34 thermodynamic and kinematic parameters evaluated, convective inhibition (CIN) emerges as the strongest discriminator: SWPE environments exhibit substantially stronger mixed-layer inhibition, consistent with a tropical “loaded-gun” profile in which delayed initiation allows instability to accumulate before explosive deep convection occurs. In contrast, CAPE shows limited separability between the two regimes. Storm-producing environments also feature enhanced downdraft potential (higher DCAPE) and a distinctive vertical wind-speed structure characterized by weaker low-level flow but markedly stronger upper-tropospheric winds, highlighting the importance of divergent outflow and jet coupling. ERA5 composites reveal coherent synoptic-scale differences, including strengthened circulation along the Thailand–Myanmar corridor and enhanced lower-tropospheric warming coupled with mid-tropospheric cooling during SWPE days. Together, these results demonstrate that capping strength, downdraft potential, and upper-level dynamical support—not buoyancy magnitude alone—are the key physical mechanisms distinguishing severe from non-severe pre-monsoon convection. The findings underscore the operational value of CIN- and DCAPE-based diagnostics for severe-weather forecasting in tropical Southeast Asia.