In the plains, the winds near the ground blow warm, moist air from the south. Farther, off the surface, the wind turns southwest and then west as you encounter the dry, warm air from the Rockies. This combination with the cold front helping to trigger the thunderstorms makes tornadoes more common in the plain states. To receive warnings in the quickest time, schools can get a NOAA weather radio that provides warnings directly by the National Weather Service. You can ask your teacher if the principal has a NOAA weather radio in the office.
Tornadoes can indeed strike large cities and have in the past.
Fortunately, the chance of a tornado hitting any one specific place is slim. Therefore, it is not often that cities are hit. There is much more open space and rural area for them to affect. About 80 percent of tornadoes are small with winds up to 115 m.p.h. Only about 2 percent of all tornadoes are considered violent, with winds over 200 m.p.h.