In what officials warn could be a regular occurrence this summer, Boulder experienced monsoon-like conditions Friday afternoon, climaxing with more than an inch of rain over a 30-minute stretch that overflowed creeks, flooded roadways and prompted evacuations.
"This is what we've been trying to educate people about," said Gabi Boerkircher, a spokeswoman for the Boulder Office of Emergency Management. "We have a really high water table right now. It's very saturated, so the ground isn't going to hold as well as it used to."
The area's highest rainfall total was measured in south Boulder, at 1.18 inches, while the Boulder County Justice Center saw 1.14 inches around 4:40 p.m. Nearly 40 percent of those totals fell in just five minutes, starting about 4:35 p.m.
Meanwhile, the foothills of Boulder County saw relatively little rainfall: No more than three-quarters of an inch were recorded in any one location.
Weather conditions calmed in the city of Boulder shortly after 5 p.m., after the pounding rain flooded roadways and prompted officials to evacuate the Boulder Municipal Building, 1777 Broadway, and the main library, 1001 Arapahoe Ave.
Cars were partly under water in low-lying areas, and at least one person reported being trapped in his car, according to police radio traffic.
Streets were flooded at Sixth Street and Canyon Boulevard, and at Baseline Road. The intersections of Balsam Avenue and Ninth Street, and Foothills Parkway and Marshall Road, experienced storm drain issues and were particularly flooded, Boerkircher said.
May is traditionally the wettest month of the year in Boulder, and the area is also contending with heavy snowmelt. But, according to meteorologist Mike Baker of the National Weather Service, recent conditions have been more extreme than expected.
"What's different about this particular May is that a lot of our rain has been coming with intense thunderstorms," he said. "It's taking on something similar to the rainy season of our summer monsoons. That's not normal.
"If we go into a dry period for maybe two or three weeks, water levels will start to come down," Baker added. "It's difficult to say if we'll have this problem all summer, but I wouldn't rule it out."
On Friday, the National Weather Service had previously issued a flash flood watch from 10 a.m. to 8 p.m. for Boulder County, including the cities of Boulder and Longmont, and the Fourmile Fire burn scar in the foothills.
A flood advisory was also issued for Lyons as minor flooding was expected along the St. Vrain River.
Baker said to expect low-threat thunderstorms Saturday, and a dry next week.
"We'll be out of this little bout of monsoon-ish precipitation," he said.
Starting Thursday, Boulder County Sheriff Joe Pelle banned tubing in Boulder Creek from Nederland to Erie because of severe danger from the high waters.