What is a QLCS tornado?

 Laura asks, "Can you explain what a QLCS is and what conditions can cause it? Often hear QLCS tornado."

QLCS stands for 'Quasi-linear convective system' which is another way of describing a line of thunderstorms, such as a squall line. These storms form along and ahead of a surface boundary, usually a cold front, but can also form along a stalled or stationary boundary. Winds at the surface help transport a warm/moist air mass while strong winds aloft help to sustain the storms. Sometimes the linear storms can initially start out as individual thunderstorms, known as supercells, before merging into the line. This often occurs late in the day or at night as the low-level jet strengthens and helps sustain the storms.

Within the linear structure of storms there can be segments that 'bow out'. These are referred to as bow echoes. Strong inflow winds combined with the rain cooled air from the storm help to push the storm out along its leading edge, giving it its bow or backwards 'C' looking shape. It's typically along the apex of the bow where we get the strongest damaging wind gusts.

North of that bow structure, however, there can sometimes be enough spin to generate mini supercell structures resulting in quickly developing tornadoes. And this is what is referred to as a 'QLCS tornado'. These types of tornadoes often occur very quickly but can also dissipate quickly. Sometimes they occur without an actual tornado warning because they happen so quickly, but the storm itself will have a severe thunderstorm warning with it, with the mention that a tornado can form at any time. This is what makes QLCS tornadoes a little more dangerous and harder to warn for. QLCS tornadoes are usually on the weaker side and don't last too long, but there have been some stronger ones that have reached EF2 or EF3 strength. 

Locally, the tornadoes that came through on the evening of March 31, 2023, developed with a strong line of storms. The strongest tornado in the local viewing area was the Woodhaven Lakes/Amboy tornado that was rated an EF2 with peak winds of 115 mph and on the ground for 9.5 miles. Thankfully there were no reported injuries or fatalies. However, a little while later an EF1 tornado developed near Davis Junction and moved through Belvidere causing the collapse of the Apollo Theatre, resulting in numerous injuries and one death. That tornado was on the ground for almost 28 miles and had peak winds of 100 mph.