A very slow-moving supercell thunderstorm dazzled storm chasers in South Dakota when it blossomed in the Black Hills near Rapid City on Monday evening.
The supercell began to develop north of Rapid City around 5 p.m. local time, but even two hours later the storm hadn’t moved more than five or six miles. Mid-level winds over western South Dakota were weak, and there wasn’t enough oomph in the atmosphere to push the storm downwind.
The parked storm caused huge rainfall totals of 2 to 5 inches (flood warnings are still in effect for creeks in the area) and very large hail up to 4.5 inches in diameter. It also allowed storms chasers were able to sit back and watch a beautiful supercell spin — something that often doesn’t happen while scouring the great wide Plains for severe weather.
“It was a photographer’s dream,” said weather.com’s Jonathan Erdman.
Our own Ian Livingston has been storm chasing for over a week now and was in South Dakota on Monday.
“We knew storms were likely in western South Dakota, but there was some uncertainty as to where they would form,” Ian said. “We positioned in Sturgis to keep northwest South Dakota and the Rapid City area both in play. The HRRR [a high-resolution, short term forecast model] really liked the northwest part of the state, but the Black Hills acts as a convergence zone and a source of lift. It’s very typical for supercells to fire off them and move east.”
It turns out his team was in great position since this storm was the only game in town Monday night.
“The supercell storm eventually popped late day once enough instability gathered to fully break the cap,” Ian said. “A number of others formed in the same location and didn’t mature. The core [of the storm] actually ended up drifting west-southwest into the hills which is fairly unusual. An outflow boundary from the south eventually hit it and helped kill it off by cutting off the moisture.”
Dan McKemy, a meteorologist for the National Weather Service, captured the photo above as well as this stunning timelapse of the storm. It really does just linger on the other side of the hill as it ingests copious amounts of moist air. You can see the moist inflow form what meteorologists call a “beaver’s tail” (because that’s actually what it looks like) on the right side of the storm.