<p>This study investigates severe nighttime thunderstorms (NT) over the southwestern Amazon Basin from 1998-2013. NT events were identified using the Tropical Rainfall Measuring Mission Precipitation Features database, based on vertical depth, horizontal extent, rainfall volume, and lightning criteria. A total of 97 NT events were selected, typically starting between 18:00 and 00:00 local time and lasting 7.5 to 22.5 hours. Most occurred near the Andes foothills, highlighting orographic influence, with a seasonal peak in October–December. Events were classified by lightning rate: 40% were intense (&gt;32 flashes/min) and 25% extreme (&gt;47 flashes/min). Two low-level synoptic patterns were identified: one linked to the South American Low-Level Jet (55 cases), and another showing a northwest–southeast low-level confluence, typically organized by frontal systems to the south (42 cases). Large-scale composites show both patterns form at least 12 hours before NT onset. Environmental composites centered on NT cores (6°×6° boxes) were analyzed for intense and non-intense cases. Intense NTs featured low-level confluence, warmer environments, increasing convective available potential energy, decreasing convective inhibition before convection, and a strong horizontal and vertical moisture contrast, especially a dry layer at 500 hPa over a moist lower troposphere. These results suggest the vertical moisture structure, notably the dry air layer at 500 hPa, plays a key role in NT severity, serving as a preconditioning factor for forecasting. The vertical humidity gradient, variables at 850 hPa, and conditions near 18:00 UTC are critical indicators for next-day NT forecasting in the southwestern Amazon.</p>