This has been common in the US this summer, and that's what happened in my location. We received around 7" of rain in 4 hours. My basin was labeled as a 1 in 300 year flood; others nearby were 1 in 1500 years.

This happened again in 2 location in the US: Missouri and South Carolina.
A disturbance stalled over Missouri this morning, dropping between 7 and 11 inches of rain in 5 hours. (First picture)
On a more localized level like in Maryland, the eastern side of Columbia SC picked up 4.64" in 90 minutes.
Upper level winds have been slow this summer abnormally. In addition, it has been slightly more moist (higher dew points) than usual. More scattered storms, and more moisture to work with this summer than normal.