On Wednesday, rotating supercell thunderstorms towered 10 miles into the sky in southwestern Kansas. Torrential downpours, hail ranging from in size from golf ball to tennis ball, and even a damaging tornado accompanied the storms. The weirdest part? It wasn’t even supposed to rain.

The unusual event came on a day when the National Weather Service’s Storm Prediction Center thunderstorm outlook showed no elevated risk of severe storms. The local National Weather Service office called for wall-to-wall sunshine, with a zero percent chance of rain.

But the atmosphere never bothered to check the forecast. About 6 p.m., thunderstorms explosively developed, soaring 60,000 feet high. Two pairs of thunderstorms each split apart, yielding four individual rotating storm cells. The southernmost one went on to produce a tornado about 7:40 p.m.

The National Weather Service said via a phone call they were rating it an EF1 tornado on the 0 to 5 scale for twister intensity. EF1s have wind speeds greater than 85 mph.

“This was completely unforecasted,” said Bill Turner, a lead forecaster at the National Weather Service office in Dodge City, Kan. “It’s got to be rare to get something like that.”

A sunny forecast

Kansas wasn’t even mentioned in Wednesday morning’s severe weather outlook from the Storm Prediction Center, with the nearest severe weather expected in parts of Texas. The tornado threat was labeled as “less than 2 percent in all areas,” meaning it was too low nationwide for the center to even delineate a threat category.

But weather isn’t an exact science, and surprises happen. Turner explained that the ingredients were in place for severe storms — as is the case many days during the summertime — but, without a viable triggering mechanism, there was little reason to believe one would form.

“We had no confidence in that,” Turner said. “We were not expecting anything like that.”

Conditions quickly change during the afternoon

Turner was on the Wednesday morning forecast shift, during which he and his colleagues noticed how unstable the atmosphere was becoming, marking the availability of fuel if storms were to develop. But that’s not unusual during the summertime, and many unstable days pass with clear blue skies. It’s like having a pit of firewood and kindling, but never lighting a match.

In the office’s area forecast discussion, meteorologists had indicated that, if any rogue storms were to form, they would likely be farther east toward Medicine Lodge and Pratt — about 100 miles away. Otherwise, the focus was on temperatures.

However, storms quickly fired about 6 p.m. The southernmost one acquired intense rotation as it moved over northern Seward County in southwestern Kansas, prompting a tornado warning at 7:38 p.m. A tornado touched down at or shortly after 7:34 p.m.

Devin Hardy, a storm chaser who calls southwestern Kansas home, captured a striking photo of the funnel lit against a bright yellow sky.

“I was eating dinner and got a ‘lightning in the area’ alert on my phone,” wrote Hardy in a Twitter direct message. “So I looked at the radar and dropped everything and took off.”

He called his catch an example of being “at the right place at the right time.”

What may have happened

Meteorologists were left scratching their heads on how a sunny forecast in an environment apparently lacking a trigger could result in towering clouds and a tornado, but Turner postulates a subtle boundary, marked by a slight temperature change over distance, could have induced just enough convergence near the surface to kick up a storm.

“We had stratus [clouds] yesterday morning that came through behind the cold front that dissipated to stratocumulus,” Turner said. “The best guess I have is there was a little differential heating boundary.”

Turner estimates the tornado was on the ground for about 10 to 15 minutes but caused little damage along its photogenic journey. While the tornado was rated an EF1, coming up with that rating was a challenge due to the lack of structures it intercepted.

“We don’t have damage indicators,” Turner said. “Sometimes there’s nothing to hurt.”

The rating was based solely on the storm’s clash with irrigation sprinklers.

“The thing is, northern Seward County is basically wheat and dirt,” explained Turner. “The only damage was [to] one of those irrigation sprinklers. That’s the only damage report I know of. It takes easily 80 to 90 mph [to move one].”

A weird year in Kansas

In addition to being unpredicted, Wednesday’s tornado occurred well outside Kansas’s “typical” tornado season, which spans six to eight weeks during May into early June. But in July, the heat is largely established, without the clashing air masses and jet stream wind energy needed to twist up a tornado.

This year has proved to be different with Kansas seeing one of its slowest — and latest — tornado seasons on record. Not a single “classic” tornado has formed in the Dodge City office’s forecast area in the year, bizarre in a place known for its reliable twisters.

“I would argue in our [county warning area], it appears this was — again kind of subjective — I’m pretty confident the only supercell tornado [of 2020], judging from the pictures,” Turner said. “It was sustained, clearly a supercell, and on the ground 10 to 15 minutes. It was real.”

Supercells are rotating thunderstorms structured about a single, persistent rotating updraft.

“We had tons of supercells this year, but there was always something to screw up tornado production,” Turner said. “Finally we get one storm that has enough [instability] and [spin] to do its thing.”

July is a notoriously difficult month for predicting thunderstorms in Kansas. Wind dynamics needed to spin thunderstorms are meager, but sometimes the buildup of extreme instability can compensate.

“This is a hard time of year out here because the ‘season’ is over, all the storm chasers leave, but we have tons of [instability] and evapotranspiration,” remarked Turner, referencing the process by which plants can add moisture to the air. “Every little tiny boundary is going to try to produce a storm every day.”

He was expecting a few more storms Thursday.