Anatomy of rare flash flood in Anthem


by Meteorologist Royal Norman

Bio | Email | Follow: @RoyalNorman

Posted on August 2, 2012 at 4:35 PM

Updated Tuesday, Oct 29 at 7:22 PM

Map: Anthem, Ariz.

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ANTHEM, Ariz. -- The clean-up continues in portions of Anthem, north of Phoenix, were up to five inches of rain fell in less than 90 minutes on Tuesday. 

There were at least two rain gauges in the area with totals over five inches, although most of the reporting stations were in the range of one to two inches.

Now, whenever that much rain falls in a localized area, there’s going to be problems. But Anthem, which is not in an official flood plain, presents some local issues that probably made things a little worse. 

In Map 1, you’ll see Anthem is bordered on the north by the New River Mountains, and to the south by Daisy Mountain and the Desert Hills area. It puts Anthem in a bit of a bowl, a mini-valley if you will.

In Map 2, we’re adding five inches of rain in 90 minutes. That’s the crazy part of this. Scientists call this a 500-year event, meaning on average, a rainfall like that right there, would only occur once every 500 years.

Map 3 shows the four major washes that run generally from the northeast to the southwest across Anthem.

Map 4 shows all the washes come together close to Interstate 17 into the Deadman Wash. That runs southwesterly across the desert plain. Where the wash crosses the Carefree Highway is where we saw several water rescues Tuesday night of people who had driven into the roadway covered with fast, flowing water.

Although everyone got out okay, first responders took the opportunity to remind us all never to enter running washes, especially at night, because we can’t tell the strength or depth of the water.