Storm chasing is broadly defined as the deliberate pursuit of any severe weather phenomenon, regardless of motive, but most commonly for curiosity, adventure, scientific investigation, or for news or media coverage. A person who chases storms is known as a storm chaser or simply a chaser.

While witnessing a tornado is the single biggest objective for most chasers, many chase thunderstorms and delight in viewing cumulonimbus and related cloud structures, watching a barrage of hail and lightning, and seeing what skyscapes unfold. A smaller number of storm chasers attempt to intercept tropical cyclones and waterspouts.

 

Note:   The above text is excerpted from the Wikipedia article Storm chasing, which has been released under the GNU Free Documentation License.