Fine-scale Phased-array Radar Observations of an EF2 Tornadic Supercell near Mountain Lee

This study presents finely resolved radar signatures of multiple cyclonic vortices associated with an EF2 tornadic supercell that occurred in Guangzhou on 16 June 2022 and discusses how the mesocyclone formed on the lee side of mountain. A nearby X-band phased-array radar provides evidence that the mesocyclone was shallow, with a depth generally confined to less than 3 km. The mesocyclonic feature was observed to initiate from near-ground level, driven by the interaction between intensifying cold pool surges and shallow lee-side ambient flows. It was first recognized shortly after the presence of near-ground cyclonic convergence signatures over the leading edges of cold pool outflows. Over the subsequent 17 min, the mesocyclone developed upward, reaching a maximum height of 3 km, and produced a tornado 8 min later. Nearly coinciding with the time of tornadogenesis, a noticeable separation of the low-level tornado cyclone from the midlevel mesocyclone was observed. This shift in the vertically oriented vortex tube was likely caused by modifications to the low-level flow due to the complex hilly terrain or by occlusions associated with rear-flank downdrafts. After tornadogenesis, high-resolution X-PAR observations revealed that the lowest-level mesocyclonic signature contracted into a gate-to-gate tornadic vortex signature (TVS) at the tip of hook echoes. Compared to conventional S-band operational weather radars, rapid-scan X-PAR observations indicate that a core diameter threshold of 1.5–2 km could be employed to identify a cyclonically sheared radial velocity couplet as a TVS, potentially extending the lead time for Doppler-based tornado warnings.