Mesoscale Convective Systems: the culprit behind the 4th of July severe weather

If your 4th of July plans involved scrambling indoors as a wall of dark clouds rolled over the Lake of the Ozarks, you aren't alone. This past holiday weekend, Central Missouri got hit by a massive cluster of storms that knocked out power for thousands across the area, downed large trees on homes, and blew over smaller structures.

This wasn't just your typical, run-of-the-mill summer afternoon thunderstorm. It was an MCS, and we are closely monitoring the weather setup for tomorrow to see if the environment will be favorable for it once again.

MCS stands for Mesoscale Convective System. In plain English, it's a massive, self-sustaining storm machine.

While a normal summer thunderstorm relies on local afternoon heat and behaves like a "one-and-done" burst of energy, an MCS is a highly organized team of thunderstorms. They pack together into a giant linear complex that can stretch across entire states and travel for hundreds of miles. These are storm systems that last for 12 hours or more, and they feed themselves through physics. As heavy rain falls, it cools the air around it. This rain-cooled air is incredibly dense, so it drops rapidly to the ground and pools up into what is called a "cold pool."

Think of this cold pool as an atmospheric snowplow. It pushes across the landscape, forcing the warm, humid air ahead of it up into the sky. That forced lift triggers new storms continuously along the leading edge, keeping the entire machine alive for hours.

When you look at an MCS on a radar loop, you will often see the leading edge bulge outward like an archer's bow. This signature radar characteristic is called a bow echo. That bow tells us that a strong stream of fast-moving air aloft, also known as the rear inflow jet, is slamming down into the back of the storm line. When that wind hits the ground, it rushes forward violently, producing the intense, straight-line winds that rip down trees and power lines.

Fast forward to tomorrow, Thursday, and the ingredients are coming together to, at the very least, observe damaging winds from storms, which could be caused by an overnight MCS that moves into the area by the afternoon hours.

Although the setups from the 4th of July compared to Thursday are similar, there is still uncertainty on if it will evolve into the type of complex that was observed this weekend. Because an MCS creates its own areas of lift due to the cold air exiting the storm, it leaves behind what is known as outflow boundaries. Think of these as miniature fronts that can be used to initiate storms at any point in the day. These leave behind a messy atmospheric footprint, and this messiness is something that computer models struggle to predict, especially when it comes to figuring out where these invisible boundaries will settle overnight.

If morning sunshine heats one side of a leftover boundary tomorrow, this would be exactly where the MCS could ignite, potentially shifting the strongest portions of the storm dozens of miles away from where the original models suggested.

We will be tracking the radar closely through the morning, as the threat of strong to severe storms potentially causing 60 mph winds Thursday afternoon and evening was enough for an ABC 17 Stormtrack Weather Alert Day to be issued.