Smart Exchange has a TON of great activities already created (for you lucky SmartBoard teachers!) to talk about tornadoes, hurricanes, and blizzards. The kids LOVE them and it actually is a great class management technique because I only call on those that have been sitting quietly and not raising their hands like monkeys (ooh ooh ooh!)
I also found these awesome videos on the National Geographic website. They are very informative and who doesn't like a quick video?