Pulse storms get their name from the quick way they form and dissipate. They are generally defined as being thunderstorms in which there is a brief, but stong updraft followed by a short period of severe weather. Before and during the time severe weather stage, the storm dissipates as quickly as it formed. Pulse storms usually do not produce tornadoes, but can and do produce powerful and widespread straight-line winds.
On a typical summer day, sunlight heats the ground, and thermals form due to the localized heating of air. Thermals are a form of instability, a term used to describe what happens when when some regions of air are heated more than others. Warmer regions, or "packets" of air accelerate upwards (because they weigh less) and displace the air that was previously there. These packets of air (colored red in the picture) continue to rise, slowly releasing their heat to the atmosphere. This cooling effect is heightened (no pun intended) as more and more altitude is gained, and at some point, the temperature of the air packet becomes like that of the surrounding air, in which case all upwards motion stops because there is no difference in buoyancy.
While the air packet is ascending, (and dropping in temperature), water droplets within the packet begin to condense upon one another and get heavier. This happens until the droplets are large enough that the air currents that lifted them can no longer support their weight, and the droplets fall to the ground as precipitation. As millions of these droplets fall, they pull and tug at the air around them, and therefore form what is called a downdraft. These downdrafts are shown as green arrows in the picture.
At this point in time, we have two things going on simultaneously. We have an updraft, and also a downdraft. What happens next is relatively simple, but very important in the life cycle of a pulse storm. As the downdraft falls through the cloud base and approaches the ground, it has nowhere to go so it spreads out. As it spreads, it begins to cut into the updraft that fueled the storm in the first place. As more and more rain falls from the upper levels of the storm, a stronger and stronger downdraft is formed, causing the downdraft to spread out across the ground even more, which then chokes out a little more of the updraft.
Eventually the downdraft completely cuts off the updraft, and since there is no more updraft to lift moisture, the entire storm becomes downdraft-dominated and rains itself out.
Nothing but the anvil is left, in the form of a wispy, high-altitude cirrus formation. Based on years of radar observation, this altitude is approximately 15,000 to 60,000 feet in extreme South Texas near the Gulf of Mexico.
