This 640 x 480 pixel image shows how a supercell thunderstorm erupts when warm, moist air breaks through an overlying stable layer and moves upward through cool, dry air. In the Northern Hemisphere, the updraft is tilted to the northeast and rotates anticlockwise when viewed from above. The warm air parcels decelerate in the stratosphere, fall back down and spread sideways in the "anvil." In the northeast part of the storm, rain falls out of the tilted updraft into mid-level dry air, cooling it and causing it to sink. The supercell's rotation pulls some of the rain and the cool air around to the southwest side of the storm. Near the ground, warm air and rain-cooled air meet in a turbulent boundary called the gust front. Lowered wall clouds and tornadoes tend to form along this line, near a cusp marking the storm's center of rotation.
