LAUSR

Abstract An EF4 supercell tornado that occurred on 23 June 2016 in Funing, China is simulated using the WRF model. Five nested forecast experiments are run, with the horizontal grid spacing of the inner-most nest being 4000, 1333, 444, 148, and 49 m, respectively. All experiments reproduce the general characteristics of the observed supercell storm, but tornado-like vortex does not develop until the grid spacing is 444 m or less. The tornadoes on the 444, 148 and 49 m grids reach EF1, EF2 and EF3 intensities, respectively. The tornado vortex simulated on the 444 m grid tends to maintain a one-cell structure, while a ring of high-vorticity develops during the mature stage of the tornado vortex on the 148 m grid leading to a two-cell structure. On the 49 m grid, microscale vortices along the outflow boundary merge into and help organize the main tornado vortex while multiple ‘suction vortices’ develop later along the high-vorticity ring leading to a multi-vortex tornado. These sub-vortices create localized regions of intense winds due to the super-positioning of the sub-vortex and main vortex circulations and the system translation speed. Sub-vortices also create irregular strong surface wind patterns with localized ‘damage cores’, broadening the tornadic wind swath; these are consistent with the Funing tornado damage survey. Based on the results, we recommend a horizontal grid spacing of at least 500 m for real-time warn-on-forecast applications in order to capture tornado-like vortices while for tornado dynamics, prediction and predictability studies 50 m or less is recommended.