Flash flood watch to encompass Valley, beyond starting Thursday

PHOENIX – It’s probably time to break out the heavy-duty rain gear in Arizona. A good portion of the state is under a flash flood watch starting Thursday afternoon in advance of a monsoon storm.

“We are looking at quite the system for the monsoon,” National Weather Service Phoenix bureau meteorologist Mark O’Malley told KTAR News 92.3 FM early Thursday.

The flash flood watch is set to last from 5 p.m. to 11 p.m. Saturday. During that stretch, chance of rain jumps from 30% late Thursday afternoon to 60% late evening and then 70% Saturday, a day when heavy rain is expected.

Showers could drop anywhere from one-tenth of an inch to a quarter-inch during those days, forecasts showed.

“Typically, in the monsoon we don’t look at predictable systems, however this one is … potentially bringing some locally heavy rains to many parts of Arizona over the next couple of days,” O’Malley said.

⚠️Over 8 million people are under a Flash Flood Watch across portions of the Southwest as the monsoon continues to impact the region. Widespread heavy rain is expected through the end of the week with flash flooding possible, especially near washes, urban areas, and burn scars. pic.twitter.com/X7ddBMq6wQ

— NWS Weather Prediction Center (@NWSWPC) July 22, 2021

Here's a look at the 24 hour rainfall. The potential for flash floods & heavy rain remains in the forecast throughout the week. Read our daily weather outlook & adhere to all the NWS guidance. Real-time rainfall/streamflow data is always available at https://t.co/yNJEM14Yye #azwx pic.twitter.com/4f5UgqmmIw

— The Flood Control District of Maricopa County (@FCDFloodInfo) July 22, 2021

Rain fell in the Valley on Wednesday, from very little in some parts — 0.04 inches in Glendale and Tempe — to 0.71 inches near Fountain Hills, according to the Flood Control District of Maricopa County.

The origins of the coming storm is different than usual, O’Malley said.

“Instead of systems coming off the Pacific [Ocean], we’re looking at this system coming from the plains and Texas.

“It’s going to move right over Arizona and tap into all the moisture that we already have in place,” he said.

Humidity was 55% in the Valley on Thursday morning.

“Last monsoon we only briefly got into the wet part,” O’Malley said. “This year we’ve had a really good support in the atmosphere to produce day after day after day of rain somewhere in the state.”

The Valley has collected 0.54 inches of rain since monsoon season officially began June 15.

Aside from bringing much-needed rain, the storm will bring down local temperatures.

After a high Thursday of 104 degrees, temperatures will take a dive to the mid-90s. Friday could top out at 95 degrees, followed by two days of 93 degrees.

KTAR News 92.3 FM’s Jim Cross contributed to this report.

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