I saw this tornado cell coming at us at about 45-50 miles per hour

A large TVS (tornado vortex signature) thunderstorm super cell passes over storm chaser Brad Mack in Graham, Texas on April 23, 2014.

"I was covering the Tornado and Dixie Alleys, areas of the central and southern United States which are vulnerable to strong tornadoes, due to the severe weather forecast for that week.

We had been chasing the storm for almost 18 hours when I saw this tornado cell coming at us at about 45-50 miles per hour. With very little time, I had to quickly switch to a wider lens to capture the storm coming over us. The image shows just how big these cells are and how close we had to get to create the image. I had one chance to get the shot and I'm just happy I was able to switch lenses in time."