Meteorologist Warns This Is the No. 1 Sign a Tornado Is Brewing

The unfortunate truth is that severe weather events tend to catch most people off guard. In the case of tornadoes, what starts as a string of thunderstorms or a passing front can quickly escalate into a serious emergency. The best weather forecasts typically include some kind of warning if there’s even a remote possibility that one will touch down in your area. But if you’re looking to stay safe, meteorologists say there’s one important sign that a tornado may be brewing near you.

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Rotating rain curtains are a typical element of tornado-producing supercells.

We all have our own red flags about approaching bad weather. For some, it’s noticing that wildlife has gone eerily quiet. For others, it’s rolling thunder in the distance as the daylight takes on an odd hue. But there’s one specific element that might alert you to a serious tornado touching down, according to meteorologist Matthew Cappucci.

In a recent piece in The Washington Post, Cappucci explains that he was stormchasing through the Oklahoma Panhandle earlier this month when he saw something not far ahead that made him realize conditions were about to get much worse.

“The rain was pouring down in torrents—it was visible as dark curtains descending from the clouds,” he explains. But while the raindrops hitting the windshield of his vehicle were blowing left to right in the wind, he could see about 100 yards ahead that the droplets were moving in the opposite direction.

“The National Weather Service (NWS) had issued a tornado warning, but I’d lost cell service roughly 30 minutes earlier. I was flying blind,” he wrote. “With a start, I realized what was going on: The tornado was about to form over me.”

According to the NWS, the most common indicators of severe weather include a flanking base of clouds ahead of a precipitation-free zone closer to the ground, high-reaching cumulonimbus and mammatus clouds, and what’s known as a wall cloud that pokes below taller clouds just behind the rain-free area.

The agency explains that even though a wall cloud can linger for 10 to 20 minutes without a tornado forming, it can also begin to show rotation. This can sometimes be spotted by noticing smaller clouds along the line being sucked upwards as the wall cloud moves.

As the cyclonic nature of a tornado suggests, this sudden updraft is accompanied by a rear flank downdraft (RFD), which can either look like a clear or bright spot to the southwest of the wall cloud or as curtains of rain, according to NWS.

In Cappucci’s case, his location meant that the torrents of rain could be covering up the visible condensation funnel that officially signifies a tornado when it touches the ground. Thankfully, picking up on the droplets’ movements helped him realize where he was heading.

“I was navigating into the rotating part of the storm from the north and was in a region meteorologists call ‘the Bear’s Cage,'” he explains. “If I wasn’t careful, I’d drive straight into a developing tornado.”

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Cappucci caught his harrowing encounter on video.

Like any storm-chasing meteorologist, Cappucci took out his camera and filmed the developing tornado. After noticing the “disorienting” dancing sheets of rain in front of him, he saw the funnel cloud begin to drop towards the ground.

“A few moments later, I was driving east on Highway 64 in rural Cimarron County,” Cappucci wrote in The Post. “To my right, or south, the funnel descended, suddenly becoming more readily visible as moisture in the vortex condensed.” He explains that when a tornado touches down, the vortex becomes more intense and causes a sudden drop in air pressure that in turn causes atmospheric moisture to condense.

Cappucci says the tornado was only visible for a couple of minutes before he lost it again in the thick rain. He estimates that it was likely producing solid 120 mph winds, but without data from contact with a building or object, the NWS ranked it as an “EF-U” (or “unknown”) on the Enhanced Fujita Scale that’s used to determine a tornado’s strength.

“Seeing the rotating rain curtains up close was spectacular as a meteorologist—albeit ominous. It compelled me to slow down and pause as the developing circulation crossed the roadway,” he explains.

There are a few other signs a tornado is about to form.

Since not all tornadoes are accompanied by rain, it can be helpful to keep an eye out for other clues. According to the NWS, this includes inflow bands, which are “ragged bands of low cumulus clouds extending from the main storm tower usually to the southeast or south.” Because these formations suggest a gathering of low-level air, it could signal intensification, especially if they appear to be spiraling.

Another hint could be what’s known as the “beaver’s tail,” which the NWS says is “a smooth, flat cloud band extending from the eastern edge of the rain-free base to the east or northeast,” typically skirting near the southern edge of where it’s raining or hailing. The agency says its presence indicates that rotation is likely.

But even with so much to look for, not everything is perceptible to the naked eye. The NWS emphasizes that tornadoes can still be in contact with the ground even if there isn’t a visible cloud funnel. Because of this, you should seek shelter if you receive a tornado warning for your area.