shown that illustrates a vortex sheet roll-up prior to tornadogenesis. Notice how the vertical vorticity is concentrating in the area where the eventual tornado is generated; also notice the individual smaller vortices in the rear flank that appear to be “feeding” the larger vortex, consistent with the theory proposed in [@vortexgas17].

![Vortex sheet roll-up in CM1 simulation at $z=50$ meters and $t=158$, $159$, and $160$ minutes. Vertical vorticity is shaded, vertical velocity is contoured in $1$ m s$^{-1}$ intervals beginning at $1$ m s$^{-1}$, and horizontal wind vectors are plotted as arrows.[]{data-label="fig:vortex_image_time_series1.pdf"}](158min_v2.png "fig:"){width="77.00000%"} ![Vortex sheet roll-up in CM1 simulation at $z=50$ meters and $t=158$, $159$, and $160$ minutes. Vertical vorticity is shaded, vertical velocity is contoured in $1$ m s$^{-1}$ intervals beginning at $1$ m s$^{-1}$, and horizontal wind vectors are plotted as arrows.[]{data-label="fig:vortex_image_time_series1.pdf"}](159min_v2.png "fig:"){width="77.00000%"} ![Vortex sheet roll-up in CM1 simulation at $z=50$ meters and $t=158$, $159$, and $160$ minutes. Vertical vorticity is shaded, vertical velocity is contoured in $1$ m s$^{-1}$ intervals beginning at $1$ m s$^{-1}$, and horizontal wind vectors are plotted as arrows.[]{data-label="fig:vortex_image_time_series1.pdf"}](160min_v2.png "fig:"){width="77.00000%"}

In order to compute maximum vorticity at different length scales $\varepsilon$, the vorticity field valid on the $75$-m simulation grid was filtered using 