Jet Superposition and a Cut-off Low Behind a Rare Heavy Hailfall Episode in the United Arab Emirates (10–12 February 2024)

Abstract. Coupling between the polar and subtropical jet streams resulted in jet superposition and attendant upper-tropospheric divergence over the Arabian Peninsula, coincident with a southeastward-advancing Cut-Off Low (COL). On 12 February 2024, the associated convective system generated widespread, surface-verified hailfall across parts of the United Arab Emirates (UAE). This study examines the synoptic- and mesoscale evolution of this event using ECMWF operational analyses, CAMS reanalysis data, radiosonde soundings, satellite remote-sensing products, and radar-derived hail diagnostics. In view of the extensive regional dust plume present in the pre-convective environment, CAMS aerosol fields were analysed to assess the degree to which elevated dust layers modulated thermodynamic stability and moisture transport throughout the event. A COL developed south of Iraq, propagated southeastward, and subsequently interacted with a low-level baroclinic zone. Moisture advection from the Red Sea and the Arabian Sea was mediated by the Red Sea Trough (RST), thereby enhancing atmospheric instability. After an initial weakening stage, associated with mid-tropospheric drying and reduced low-level inflow, the convective system underwent re-intensification over the Arabian Gulf. Radiosonde observations from Abu Dhabi at 0000 UTC on 12 February indicated near-saturated conditions from the surface up to approximately 500 hPa, overlain by a comparatively dry mid-tropospheric layer. Concurrent EUMETSAT RGB composite imagery—optimized to depict dry-air intrusions and jet-related structures—exhibited upper-tropospheric signatures consistent with renewed deep convective development. Radar-derived hail products demonstrated that the period of most prolific hail production coincided with the convective system’s mature stage, during which Hail Mass Aloft (HMA, > 100 kilotons) and Vertically Integrated Hail Mass (VIHM, > 2 kg m⁻²) exceeded operational thresholds typically associated with a high probability of hail reaching the surface. The prevailing thermodynamic and microphysical environment was favourable for substantial hail deposition at the ground, whereas aerosol–radiation interactions appeared to be of secondary importance and did not exert a material influence on storm evolution relative to jet dynamics and moisture transport.