1.   Cities have often been cited as shields against tornado formation.

2.   The change in wind speed with height, called wind shear, creates the twisting motions that can lead to tornado formation.

3.   Urban environments have often been called shields against tornado formation.

4.   Urban environments and mountainous terrain have often been cited as shields against tornado formation.

5.   Urban environments have often been cited as shields against tornado formation.

6.   While hurricanes and tornadoes are very different, the strong winds of a hurricane promote the conditions necessary for tornado formation.

7.   While hurricanes and tornadoes are very different storms, hurricanes at landfall promote the conditions necessary for tornado formation.

8.   While hurricanes and tornadoes are very different kinds of storms, hurricanes at landfall often promote the conditions necessary for tornado formation.