How Wednesday’s Picayune tornado developed

Published 8:30 pm Saturday, October 30, 2021

By Skip Rigney

The tornado that touched down in Picayune on Wednesday evening was embedded in a line of strong thunderstorms that had begun earlier that day in east Texas and then rolled across south Louisiana. The storms were caused by a potent cyclone, an alternative term for low pressure system, centered near Memphis. The cyclone’s circulation covered an immense area of over one-half million square miles from Wisconsin to the northern Gulf and from Oklahoma to North Carolina.

Because of the cyclone’s intensity, the abundance of warm, humid air from the Gulf, and changing wind directions with height, the National Weather Service (NWS) issued several tornado watches on Wednesday across the Gulf South, sounding the alarm that conditions were favorable for tornadoes and severe thunderstorms.

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They issued a tornado watch for south Mississippi and southeast Louisiana, including Pearl River County, at 1:55 Wednesday afternoon, effective until 10:00 p.m. that evening.

As the squall line moved across Pearl River County, the NWS’s radar in Slidell detected a particularly strong storm embedded in the line near Picayune moving northeast at 45 mph. At 6:49 p.m., meteorologists at the Slidell office issued a severe thunderstorm warning for southeastern Pearl River County.

Moments later, radar evidence hinted that the thunderstorm might be generating a tornado. Embedded in the large area of raindrops blowing away from the radar, raindrops over a small area near Picayune were blowing back toward Slidell, indicating the thunderstorm was rotating.

In addition to the radar’s pulse of energy being reflected from raindrops, some energy was being reflected back to Slidell from a mixture of larger objects. That is often because debris is being lifted up into the air.

So, at 6:52 p.m., three minutes after issuing the severe thunderstorm warning, the NWS in Slidell issued a tornado warning stating that “a severe thunderstorm capable of producing a tornado was located near Picayune, moving northeast at 40 mph.”

The next day NWS meteorologists from Slidell came to Picayune to conduct a damage survey. They concluded that it took less than five minutes for the tornado to touch down south of East Canal Street, cross I-59 just north of Boley Creek, and then dissipate just south of Sycamore Road, a path just over two miles long. At its widest, the twister was a little wider than a football field. They estimated peak winds were 110 mph.

Wednesday’s storms also produced heavy rain. Two to five inch totals were common across the county. Some locations in the Wolf River drainage area in eastern Pearl River County received nearly six inches.

After the storms passed, a cool front swinging around the cyclone swept through the area late Wednesday night. The cyclone has been moving slowly northeast and today covers much of the eastern seaboard of the United States.

That puts us in a northwest flow for the weekend, and the cool, dry air mass that has blown into our area should hang around until Tuesday or Wednesday. By Thursday another cool front is forecast to approach our area.

However, the weather models are predicting that the cyclone associated with that front will be much smaller and weaker than this week’s.

So, any showers that do form with the front are expected to be light, and the risk of severe weather low.