Blame the moist and humid air over Kansas City, as well as the path that the storms took, for all that flooding Thursday.
“We had an extraordinary moist and humid air mass in place — not unlike something you may find over the Amazon rainforest,” said Andy Bailey, warning coordination meteorologist for the National Weather Service in Pleasant Hill, Mo.
“As the storms developed, there was a tremendous amount of moisture to work with. It was almost like they came through and wrung the moisture out of the atmosphere.”
That made the the storms very efficient in producing rain — at one point rain was falling in some areas at the rate of 5 inches per hour.
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“That is kind of on the top end of what is possible on Earth,” Bailey said.
The storms were following the same path, much like train cars on a railroad track.
“One storm after another moved over the same location in the south end of the Kansas City metro area,” he said.
Rainfall totaled 5 to 7 inches in that area, with a few locations reporting more than 8 inches.
“Most of the rainfall fell at its most intense in just a couple of hours,” Bailey said. “Whenever you have that amount of rainfall falling in such a short period of time it’s inevitably, especially over an urban area, going to lead to flash flooding like we saw.”
The rain started falling mid-evening on Wednesday. The National Weather Service issued its first flood advisory for Clay and Platte counties at 9:13 p.m. The first reports of flooding came in at 9:50 p.m.
As the rain intensified overnight, the flash flood warnings for the hardest-hit areas were issued shortly after midnight.
The majority of swift water rescues in Jackson County occurred between 1 and 5 a.m. Between 3 and 5 a.m., the National Weather Service started to see impacts of flooding along Indian and Turkey creeks in Johnson County.
Indian Creek at the state line reached a record flood stage. The creek was recorded at 27.96 feet, beating the previous record recorded on June 14, 2010, by nearly 2 1/2 feet.
Tomahawk Creek also set a record when it was recorded at 20.81 feet, about 1 1/2 feet above the record set July 30, 2008.
These type of rainstorms are not rare.
“We tend to get very intense rainfall or thunderstorms like this every three, four or five years,” Bailey said. “Certainly this was at the upper end of what’s possible for rainfall in a thunderstorm in a short period of time. It’s not unique, but it is extraordinarily intense.”
The storms also produced a tremendous amount of lightning and nonstop thunder.
“I’m sure that if people weren’t impacted by the flooding, they certainly were by the thunder,” Bailey said. “I’m sure lots of people are a little bit tired around the metro today having lost quite a bit of sleep due to the storms.”
The rains moved out of the area between 7 and 8:30 a.m. While there might be a few lingering sprinkles, the amount of rainfall won’t stop the retreat of floodwaters.
No rain is expected in the near future.
“We’ll have an extended period of dry-out in the next couple of weeks,” Bailey said.