National Weather Service United States Department of Commerce


On the evening of August 20th a system moving through the region triggered strong storms across portions of east central Utah. Due to rich monsoon moisture in place these storms produced heavy rainfall. Clouds cleared out of the area by early afternoon, which allowed the instability to become maximized. As a result the storms developed very rapidly. The sounding that morning from the Grand Junction NWS had a precipitable water value of 0.93", which is 125 to 175 percent of normal.

There were two automated gauges located in Spanish Valley where the some of the highest rainfall amounts occurred. Over the course of an hour (7-8 MDT) one of the gauges measured 1.42" and the other 1.71". Lighter rain did continue for another 1-1.5 hours. These rainfall amounts yielded 50 year Average Return Intervals (ARIs) in Moab, UT and surrounding areas experiencing 100 year ARI. This heavy rainfall and widespread flash flooding resulted in numerous road closures due to flash flooding and debris flows. Numerous homes and businesses had upwards of 7 inches of water and debris inside resulting in significant property damage.

Mill Creek in Moab rose roughly 11.6 ft in about one hour. The rise started around 8:15, which was not long after the heavy rain fell. Below are the USGS hydrographs for Mill Creek below Pack Creek in Moab.

View of Shelf Cloud from NWS GJT
Flooding in Downtown Moab (Credit: Salt Lake Tribune)

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