Flash Flood Warnings are issued for an area by the local National Weather Service Office.
In Tucson, that office is located on the University of Arizona campus.
The meteorologists on duty at the time of the storms both track rain totals estimates on radar and reports from National Weather Service spotters and emergency officials.
The meteorologist use this information to determine if a Flash Flood Warning needs to be issued for an area.
Another way to track flash floods if through streamflow gauges.
These are instruments placed on washes and rivers that measure how much water is flowing through a waterway and/or how high that water flow is at any given time.
Two websites often used to track streamflow here in Southeast Arizona are the Pima County Regional Flood Control District's ALERT webpage and the USGS Streamflow webpage.
Both of these webpages have interactive maps where you can access data from the gauge.
For example, Hereford, which is a small community southwest of Sierra Vista, was hit hard by storms on Tuesday and Wednesday night.
The image below shows how high the water was in the San Pedro River in Palominas, near Hereford, after the storms.
You can see the water level come up on Tuesday night, July 9th, and then fall into Wednesday morning when the weather was calm.
But another storm Wednesday night dumped more rain in the area and the river level once again rose quickly.
But then if fell quickly once the storm ended.
The water in the San Pedro flows north through Cochise County and into extreme northeast Pima County before moving into Pinal County.
Below is a See It, Snap It, Send It of the San Pedro River still running high through St. David on Thursday.
The water levels can come up to dangerous levels in a matter of minutes during and after a monsoon downpour.
This is why it is called a flash flood.
The flooding can be severe but it doesn't often last long.
Stay safe during the monsoon and avoid flooded washes and roadways.
It only takes about 6 inches of rushing water to push a car off the road.
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