Arizona’s monsoon season is well underway.

Here are the latest updates on storm activity and forecasts affecting the Phoenix metro area.

July 13, 6:45 p.m.: Storm approaching Scottsdale

A strong storm was approaching central Scottsdale just after 6:30 p.m., the National Weather Service said. 

The storm was bringing strong winds along with it, with wind gusts of up to 40 mph possible until 7 p.m., officials said.

 

 

July 13, 5:30 p.m.: Severe Thunderstorm warning for part of Maricopa County

The National Weather Service issued a severe thunderstorm warning for areas of  northeast Maricopa County, including Carefree until 6 p.m.

 Satellite radar was showing strong storms building to the northeast and east of Maricopa County, which could produce outflow winds into eastern areas of Maricopa County.

A flood advisory was issued for areas near the Tonto Basin east of the Valley until 7 p.m., as heavy rains moved through the area.

 

 

 

July 13, 3:15 p.m.: Storms build near Flagstaff, Tucson

The National Weather Service in Tucson and Flagstaff both reported isolated and scattered thunderstorms on Thursday as later-afternoon monsoon storms again built while Phoenix remained dry.

There was a strong thunderstorm rolling over Black Canyon City north of Phoenix, delivering them heavy rainfall and strong winds. Heavy rainfall also occurred on just northeast of Payson.

 

National Weather Service Tucson said areas northeast of Safford and throughout Santa Cruz County should expect strong storms on Thursday.

The National Weather Service in Phoenix had predicted the chances of storms moving into the Valley would increase over the upcoming weekend. Storms weren’t expected to do much in the Phoenix area Wednesday, but a heavy cell moved through the northeast Valley and another hit part of the northwest Valley.

July 12: Storms roll through north Valley

A monsoon storm was rolling through northeast Phoenix and northern Scottsdale Wednesday evening, prompting the National Weather Service to issue an advisory.

In addition, a storm was moving through the Surprise area in the northwest Valley.

Severe thunderstorm warnings were issued earlier for areas near Fountain Hills and Rio Verde to the northeast, as well as far eastern Maricopa County near Tortilla Flat, the National Weather Service said.

A National Weather Service tweet said the Scottsdale-area storm was heading southeast and included gusty winds, lightning and heavy rain.

July 12: Old-school monsoon dates

If the old-school method still held, Arizona’s monsoon would have started on July 9.

The old system, last used by the National Weather Service in 2007, looked at the dew-point average to calculate the start of the monsoon.

“We took an average of the dew-points in Phoenix and when they got above 55 degrees … for three days, that is when we started the monsoon season,” Travis Wilson, a National Weather Service meteorologist.

The average dew-point temperature was 60 degrees on July 9, 58 degrees on July 10 and 61 degrees on July 11, Wilson said.

The National Weather Service officially recognizes monsoon season from June 15 to Sept. 30. According to Wilson, every regional office had different methods of determining when the monsoon began, so they decided in 2008 to declare a season by calendar.

“Just because it’s not raining in Phoenix – it takes a little longer for it to moisten up down here – doesn’t mean we’re not in the monsoon season,” Wilson said.

For the past 30 years, the first measurable rainfall of the monsoon in Phoenix has typically fallen around July 4. That didn’t happen until July 10 this year.

Thunderstorms start with three ingredients: an unstable atmosphere, moisture and a trigger. Wilson said that the mountainous regions up north see thunderstorms first and these storms produce “outflows” that travel down to Phoenix, where, if conditions are moist enough, more thunderstorms can be produced.

 

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