AccuWeather has a great video of the tornado that crossed the New York Thruway at Amsterdam, NY. Click here to view the video.
But, I want to direct your attention to the segment of the video (starting at :11) showing the "power flashes." Power flashes are a sign of high danger from a tornado or very high winds capable of producing damage. In this case, and in many others, the flashes precede the tornado. If you see them, get to shelter immediately regardless of whether you can see a tornado or not. If you are in your car, at least stop the car and pull to the sign of the road.
Hat tip: Jesse Ferrell