Multiscale characteristics of an extreme precipitation event over Nepal

Isolated convective cells organized upscale into a wide intense convective system, fuelled with moist low-level inflow. The result was torrential rain with over 250 mm within 24 hr. Several synoptic-scale conditions contributed to the intense development: (a) supply of moist air with the help of a typical monsoon break condition flow pattern, (b) anomalously significant moisture sources along this path due to prior precipitation events, (c) an upper-tropospheric trough orienting the atmospheric flow against the Himalayas with associated quasi-geostrophic forcing creating a favourable environment for convection, and (d) destabilized stratification due to an upslope flow.

This analysis encompasses multiple scales and shows how a wide intense convective system, not unusual for this region, can be intensified by distinct synoptic constituents.