When It Rains, It Pours
A cluster of strong to severe thunderstorms developed over parts of northeast Kansas on Tuesday afternoon, and proceded to drop copious amounts of rainfall over a relatively small area. Radar estimations of total rainfall from the storm system are as high as 6 to 8 inches over parts of Nemaha, Brown, Jackson, and Atchison counties, while one individual called in with a measurement of 9.25 inches of rain! Much of this rain fell in 2 to 3 hours. Any time this much rain falls over such a short period of time, the threat for flash flooding quickly increases. With this in mind, the National Weather Service issued flash flood warnings for the areas receiving the heaviest rainfall as well as points downstream. Flash flooding was reported across the warned area with several road closures taking place where creeks and streams were flowing out of their banks and crossing country roads and a few state highways. In addition to the flash flooding, hail up to the size of quarters was also reported with these thunderstorms.
So what caused this to happen over such a localized area? It was a number of ingredients that played into the final product of a significant localized flash flood event.
1.) A moist environment through a deep layer of the atmosphere
2.) A slow moving, nearly stationary, frontal boundary
3.) Plenty of instability in the atmosphere
4.) A southwesterly "low level jet stream", continuously feeding moisture into the storm system
As the slow moving front became almost stalled out over northeast Kansas, the low level jet stream intersected the front and pushed moist air up and over it. This caused thunderstorms to repeatedly develop over the same area, just north of the frontal boundary. The instability and moist atmosphere did the rest of the work, turning strong thunderstorms into very efficient rainfall producers. The result was quarter size hail and more than a half foot of rainfall!
HERE is a link to a map with storm and heavy rainfall reports. (may take a few seconds to load)
HERE is a link to the Deleware River levels at Muscotah (Atchison County). It shows a very impressive rise in river levels.
The following image (to be loaded shortly) is a radar estimated storm total precipitation. Green and Yellow indicate 1 to 3 inch estimations, Orange and Red colors indicate estimations of 3 to 5 inches, with Pink and White indicating 5 to 8 inch estimates.