The National Weather Service says the storm that swept across northern Arizona over the weekend amounted to a 100-year event.
The Arizona Daily Sun reports that those types of storms have a 1 percent chance of happening every year and that Flagstaff saw an average of 2 inches of rain per hour Sunday afternoon.
Some neighborhoods received more, causing much of the city's drainage system to be overwhelmed as streets flooded.
The forecast calls for more showers throughout the week.
Coconino County's emergency management department has installed an array of television screens at its office to better monitor flooding and other natural disasters. The screens show power outages, lightning strikes, radar, fires, streamflow measurements and rainfall gauges.
Officials say the information can help them determine whether to trigger evacuation notices.