Why 2021’s ‘Severe Weather Season’ switched from spring to summer

Weather

ST. LOUIS, Mo. – This has been a strange year for severe weather across the country. Most of our severe weather came during the summer and not during the spring.

In most years, the Woods Basement Systems Storm Runner gets its heaviest workouts in the spring months of April, May, and June. We call that “Severe Weather Season” because it’s typically the time of year when the right elements in the atmosphere come together to produce damaging winds, large hail, and tornadoes.

So, what are those ingredients for springtime thunderstorms? Well, it all starts with the warm southerly winds that come racing up from the Gulf of Mexico Winds bring up the unstable air to support the thunderstorms down here at the ground. Up at about 25,000 to 35,000 feet, the winds come from the west and southwest in the jet stream and they are a lot stronger.

That change in wind speed and direction creates what we call wind shear. Wind shear creates a tumbling or rotating tube, a horizontal tube of air that is invisible to the naked eye. It is there waiting for something to come along.

That something is a thunderstorm updraft. That will take this horizontal tube of air and tilt it verticle. The stronger the storm gets, the stronger that tube gets. Sometimes, under the right conditions, it will come down to the ground as a tornado.

Take out any of those ingredients and the chance for severe weather goes way down. That’s what happened this spring. The ingredients rarely aligned so we ended up with a cool wet spring with very little in the way of severe weather. But then came summer with multiple severe weather events driven by a different kind of set-up, one that favors microbursts and strong winds.

So, here’s how those summertime thunderstorms work. It all starts with a hot and humid day. That hot and humid air builds up on the thermals into a towering cumulus cloud… which occasionally turns into a summer downpour. This is typical of some summer afternoons.

However, there are some days like we had this summer where dry air will come in over the top of those clouds as they build up in the atmosphere. That dry air evaporates some of the moisture and the rain inside the cloud creating a pocket of colder air surrounded by the warmer cloud around. That heavier and denser air will come crashing down to the ground and explode in all directions, sometimes violently, with winds of 80 to 100+ mph. That can create damage every bit as impressive as a tornado. That’s exactly what happened here a couple of times this summer.

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