MCS is a term you may here meteorologists throw around from time to time on a newscast. That's because they are a very common phenomena in the central United States. MCS is an acronym for Mesoscale Convective System. Yes, it's 3 big scary words, but let's break it down. The first word mesoscale refers to the size of the event. Mesoscale refers to a medium sized storm… so not as small as a single thunderstorm… something considered minuscule in the grand scheme of things, and what we call microscale. A medium size event is in between the very small (microscale) and very large (synoptic scale), like a hurricane, tropical system, or a midlatitude cyclone (your basic storm with warm fronts and cold fronts). The second word is convective. Most of you know this word quite well… think of a convection oven. What happens in one? You get air circulating inside that promotes heating. Same thing goes for the atmosphere; convection is another term used for storms… that mixing of air in the atmosphere. Then you have system… I don't think that one needs any further explanation. So a Mesoscale Convective System (MCS) is a regionally small set of storms that combine to make a system that travels across the country. The term is more understandable now isn't it?
Now, that's about as precise as we can get with this type of storm. They come in all different shapes, sizes, and intensities. They can produce some of the strongest wind gusts on the planet (called a bow echo) or just produce some quick downpours and a little bit of lightning. Regardless of their strength, they provide more than half of all the summer rainfall for the Upper Midwest on average. Here are some examples of what they look like and their evolution…
Static radar image of one of these systems pushing through Minnesota
Evolution of another system pushing through Nebraska… this shows the radar image at 3 different times as it moves southeast
2 separate radar images taken 3 hours apart in Oklahoma… notice this storm system is bigger and more linear than the others indicating a stronger and possibly severe MCS