Update 3:46 p.m.: Afternoon storms heading inland
The National Weather Service says there's another chance of afternoon thunderstorms in the Inland Empire over much of the Labor Day weekend, and they could arrive in a manner that is fast and furious.
The weather service says the storms could strike Riverside and San Bernardino counties as early as Friday and continue periodically on Saturday and into next week.
Storms Thursday night flooded streets and tributaries throughout the region.
A construction worker had to swim to safety early Friday when he missed barricades on a Riverside underpass and his vehicle got stuck in water left over from a rogue storm 12 hours earlier.
In other places, emergency workers removed mud from roads and yards, restored power and started cleaning up damage from a ceiling collapse at a fire station.
Previously: Classes resumed this morning at Riverside City College. The school had been closed after a thunderstorm Thursday afternoon flooded buildings and parking lots on campus.
National Weather Service meteorologist Joe Dandrea says gauges near UC Riverside recorded at least 1.2 inches of rainfall during the downpour.
"There were probably even higher amounts that gauges weren't under so I would imagine maybe even upwards of one and a half or maybe even close to two inches may have fallen in some areas close by," Dandrea says. "When that falls in like a half an hour's time, or 20 minutes' time, it creates a lot of problems."
A flash flood watch was set to resume at 11 a.m. for the Riverside County mountains. The flood watch goes through the evening and includes the Los Angeles County Mountains, the Antelope Valley and the Coachella Valley.
NBC4 has images showing the extent of the damage so far: