Jet-streak forcing and deep moisture transport during the 7 March 2025 record rainfall in Bahía Blanca, Argentina

Bahía Blanca (38.7°S, 62.2°W) experienced an unprecedented rainfall event on 7 March 2025, officially documented by the Servicio Meteorológico Nacional (SMN) as a historical record with an estimated return period exceeding 100 years. This study provides an observationally based diagnosis of the event, testing the hypothesis that record precipitation resulted from the coupling between upper-level jet-streak-associated divergence, deep ascent and exceptional moisture transport. We combine integrated multi-satellite retrievals for global precipitation measurement (IMERG) satellite precipitation with ERA5 (fifth generation ECMWF (European Centre for Medium-Range Weather Forecasts) atmospheric reanalysis) reanalysis fields and adopt event-consistent daily metrics (24-h windows) to characterise the dynamical and thermodynamical environment. IMERG reveals a spatially organised precipitation footprint co-located with a persistent corridor of enhanced integrated vapour transport (IVT) toward south-eastern Buenos Aires Province. Over the upstream region of Bahía Blanca, upper-level diagnostics show an anomalous jet-streak configuration at 200 hPa (along-flow acceleration percentile 99.3%) concurrent with extremely rare divergence at 200 hPa (percentile 99.8%) and exceptionally strong deep ascent (minimum ω daily metric, percentile 99.9%). Vertical diagnostics indicate that moisture transport was not confined to the boundary layer: layer-integrated fluxes show substantial contributions from mid-to-upper tropospheric levels (700–300 hPa) consistent with a deep warm conveyor belt like moist airstream during the event window. Together, the results support a proximal mechanism in which an anomalous upper-level jet-streak induced extreme divergence and deep ascent that, when coupled with record-level moisture transport, produced the observed catastrophic rainfall.