Rain cooled air that has rushed down & out of a thunderstorm is called a downdraft. A Gust Front is the leading edge of this cooler air as it clashes with the warmer surface air surrounding it. As the front surges forward, the warmer air it encounters is forced upward...leading to the development of what's known as a Shelf Cloud. The Shelf Cloud looks a little spooky or ominous as it hangs low and stretches forward from the base of the storm it's attached to.
Gust fronts are impressive because temperatures can drop dramatically in a short amount of time in its wake. Therefore, in a sense, it's like a small-scale cold front. Not only do temperatures drop, but as soon as the Gust Front passes an area...the winds usually shift directions & turn gusty (sometimes reaching severe limits with gusts at or above 58mph). Typically, Gust Fronts & Shelf Clouds are affiliated with severe storms.
Locally, we've recently experienced the effects of a Gust Front. On Sunday, May 6th, a complex of storms rolled into our area from north/central Alabama. The temperature was 88 degrees in Mobile at 4pm...the Gust Front and associate storm complex rolled into the city...then by 6pm, the temperature had dropped to 68 degrees. That's a 20 degree difference in 2 hours.
Meteorologist Deitra Tate