Once in a Century Storm Hits Phoenix

On Tuesday, August 2, over 2 inches of rain flooded west and central Phoenix in about an hour. major roads and highways were rendered impassable by six to 18 inches of water. Several drivers needed to be rescued from flooded cars. Fortunately, no injuries were reported.

Parts of the Phoenix area will again be vulnerable to heavy rain Wednesday evening, with the potential of 1-2 inches in some spots, the weather service predicted. Nearly the entire state of Arizona, along with portions of Eastern California, Nevada, Utah, Colorado and New Mexico were under a flood watch for later Wednesday.

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.

Monsoon storms are frequent this time of year in the Desert Southwest. July and August are typically Phoenix's rainiest months.

Though the rain itself is popularly called a "monsoon," the term scientifically means a seasonal shift in wind direction. It's derived from the Arabic mausim, meaning "season," according to the American Meteorological Society.

The Southwest monsoon is not nearly as intense as the Asian monsoon, which often brings catastrophic flooding to India and other nations.

Miami also saw an unusually stormy Tuesday. Streets were flooded due to heavy rain and flights at the city's airport were halted due to lightning, the Miami Herald reported. Miami picked up 3.79 inches of rain, a record for Aug. 2, the weather service said.

Overall, Miami sees plenty of rain in the summer. August is typically the city's 3rd-rainiest month, with almost 9 inches of rain on average.