Wow, that was close. I'm glad that your home and family were spared. Actually tornadoes can occur anywhere in any season but they are most common in the plains states (known as tornado alley) in the springtime. They are caused by instablility in the upper atmosphere (the clashing of warm, moist south air with cold north air), which sometimes results in cloud rotation. They don't always reach the ground but when they do the results can be devastaing, as you've recently witnessed, and they can do some very freaky things. To answer your other question, I live in Texas and we have all kinds of weather. Lately, it's been very cold and windy at my location. There was a mild earthquake nearby recently which is rather unusual for this area.