Rain storm in Arizona

The drenching monsoon rain that brought widespread flooding to the Phoenix area late Tuesday was a 1-in-100 year storm and just the latest historic storm to drench the nation.
A 1-in-1,000 year storm brought destructive flooding to the small Maryland town of Ellicott City last weekend. That event also marked at least the 9th 1-in-1,000 year rainstorm since 2010 and the third of 2016, following ones in Texas and West Virginia.
Overall, heavy rainstorms have been increasing over the entire U.S., most dramatically in the Northeast, the National Climate Assessment, a federal report said in 2014. ​A report by the National Academy of Sciences released earlier this year said a link between heavy rain events and global warming can be made with a "moderate" amount of confidence.
A 1-in-100 year rainstorm indicates that amount of rainfall in such a short time has a 1% chance of happening in any given year in a given location. A 1-in-1,000 year storm has a 0.1% chance of happening.
On Tuesday, more than 2 inches of rain pounded west and central Phoenix in about an hour, flooding major roads and highways. Several drivers needed to be rescued from flooded cars, but no injuries were reported.

http://www.usatoday.com/story/weather/2016/08/03/phoenix-arizona-monsoon-storm-floods/88002936/