Slow-moving thunderstorms in the mountains have much of western Colorado under a flash flood watch until 9 p.m., according to the National Weather Service.
Storms could extend into the foothills as an upper-level disturbance in the atmosphere sweeps in from the southwest, forecasters said.
The area of concern includes South Park, Summit County, Kenosha mountains, the east slope of the Mosquito Range, as far west as Rabbit Ears and Medicine Bow ranges, including Rocky Mountain National Park.
As much as 2 inches of rain an hour is expected at times, which could create mud or rock slides, forecasters warned.
A flash flood warning is in effect in southwestern Jefferson County until 5:15 p.m. after a storm dropping heavy rain was picked up by radar.
Lowland areas and some roads could flood, they warned.
The metro region has about a 20 percent chance of isolated showers or thunderstorms this afternoon and 40 percent tonight, forecasters said.
After a high of about 90 degrees on Monday, there will be a 50 percent chance of showers Monday night, according to the Weather Service.
