Analysis of low-precipitation supercell-induced tornado event under ambient dry conditions in a mountainous region

An analysis of two EF1 weak tornadoes that occurred in Weichang and Longhua including the pre-storm environmental conditions and fine structures is conducted based on observations of radars on different bands and wind profile radars. The results show that the tornado occurred under the background of northwesterly flows behind a 500 hPa cold vortex, and the tornadic supercells were triggered by the dryline and its associated surface convergence. The supercell tornadoes occurred in the pre-storm environment with strong convective available potential energy (CAPE) and 0—6 km vertical wind shear, while water vapor at the low level and 0—1 km vertical wind shear significantly increased. The thunderstorm activity in the afternoon improved low-level moisture. The reflectivity of these two tornadic supercells was overall less intense with that of the Weichang tornado less than 40 dBz. The area was small and the precipitation near the tornado was less than 2 mm. The rotating updraft corresponding to the mesocyclone and the hook echo head were separated from the precipitation echo. Both of these two tornadic storms exhibited low-precipitation (LP) supercell characteristics. In this paper, the pre-storm environment and structural evolution of the two LP supercell storms are recorded. Moderate mesocyclone at low levels and tornadic vortex signatures (TVS) were identified, indicating the X-band radar can capture the LP supercell tornado. The occurrence of the TVS corresponded well with the occurrence of the Weichang tornado, and the Longhua TVS was detected 8 min in advance, indicating that the leading time for the LP supercell tornado warning was limit.