Abstract:Using CINRAD data, sounding data, data of automatic meteorological observing stations, disaster investigation reports and ERA5 data, the environmental physical quantities, storm evolution, low-level small-scale vortex and dual-polarization characteristics of the outbreak tornado events in Shandong on 5 July 2024 are analyzed. The results show that under the extratropical cyclone situation, outbreak tornadoes are generated east or northeast of the ground low-pressure center, and the low-level jet is strong. Strong vertical wind shear at low altitudes, storm relative helicity and large energy helicity index are the key environmental factors for tornado outbreak. Six tornadoes are generated near the strong 3-h negative pressure change zone with the easterly airflow on the ground. The supercells/bow echoes within quasi-linear convective systems or the newly developed supercell storms in the warm zone in front of linear convective systems are efficient in producing tornadoes. The rapid decrease of the strong vortex center or the rapid increase of the partial radial velocity in the low level is a precursor to the generation of small-scale tornadic vortices. Eight mesocyclone tornadoes are characterized by strong mesocyclones with the rotation speed exceeding 20 m·s-1 in the low level, and one non-mesocyclone tornado is induced by bow echo with rear inflow jet of 42-45 m·s-1. The tornado in Dongming County is the most damaging and lethal tornado, whose parent storm has the strongest updrafts. The width of the low-level tornadic debris signature (TDS) is about 2km, and the top of the TDS reaches about 9 km, showing a dispersed state with the maximum width of about 4 km.