The Government weather forecast expected 200mm precipitation, but it ended 441.5mm.
The flooded river had a section going through mountains just like a bottleneck. That narrow section made the water to accumulate and flood.
The workers working in the nursing home with 14 dead seniors witnessed water coming so fast that they could not move all the seniors to upstairs. It took only 10 minutes from trickling to flooding.
Space Traveler in Alabama 