Boulder registers wettest 24-hour period, and month, on record

Boulder has set a record for its wettest 24-hour period. Ever.

Prior to Wednesday, the single wettest day on record was July 31, 1919, when 4.80 inches of rain were recorded, according to Bob Henson, a science writer at the National Center for Atmospheric Research.

Henson said that the latest official readings for Boulder show that from 6 p.m. Wednesday to 9:15 a.m. today, 7.21 inches of rain have fallen in Boulder, with amounts likely varying from a bit lower in northeast areas of the city to higher than that to the southwest.

"We have never had anything this big," said Boulder meteorologist Matt Kelsch.

Additionally, the last three days of rain are more than Boulder has experienced in any month on record.

Since the rain kicked in late Monday afternoon, Boulder has officially recorded at least 9.61 inches of rain, topping the 9.59 inches recorded in the entire month of May 1995.

But the numbers, in fact, go higher

"There was 10.35 inches (since Monday evening) at my house in South Boulder, and I think over toward northwest Boulder, in the Holiday neighborhood, and some other areas, they are at 11 inches," Kelsch said. "They had 8 1/2 inches just yesterday, north of Pearl St."

By late 4:30 p.m.Thursday, Kelsch said another 1.21 inches had brought the total at his south Boulder residence to 11.36 inches since the storm ended, and that since it was still raining, it might already be at 12 inches. By contrast, he said, downtown Lyons had received only 6.06 inches since Monday, but that the totals west of there were surely far higher.

Kelsch added that reporting is not as thorough for areas such as Nederland and Allenspark, but that he believes totals for the storm in and around those mountain communities will be higher.

This is also by far the rainiest September ever for the city.

"Keeping in mind that Boulder records are a little bit spotty in places, but this is an extreme event for any month. But for the month of September, the heaviest rainfall (previously) was 3.05 inches, and that was Sept. 4, 1901," Henson said.

"So we may have doubled that record, and no other September day has received more than three inches. This is a one-day record (for any month)."

In fact, Boulder's one-day record has not just been broken; it has been shattered. After the 4.80 inch reading in 1919, all runners-up rounding out the Top 10 for a 24-hour-period are readings of 3.6 inches or less. Also, all of those feel between April and early August.

So both in totals and timing, Henson said, "This is an event that really stands apart."

Prior to the drenching of the past 24 hours, watchers in parts of Boulder had recorded up to 5 inches of rain through Tuesday.

And it's not over.

National Weather Service meteorologist in charge Nezette Rydell said this morning, "Even though we are on the downside of this system, we could expect problems anywhere on the Front Range today, possibly even tonight, and start looking for improvement to begin on Friday.

The chance of rain is expected to drop -- finally -- to about 30 percent Friday night and Saturday, she said, before climbing back to 50-to-60 percent, Saturday night and Sunday.

Preliminary readings show that Boulder Creek reached 3,100 cubic feet per second at Broadway on Wednesday night, according to Treste Huse, a hydrologist for the National Weather Service.

And with more rain in the forecast tonight, "We're definitely watching it because the soils will be saturated," Huse said.

"Water is already standing, and we have another risk of flash flooding, so we definitely are still concerned."

Boulder has long ranked as one of the state's top flood hazards and made a national list of six "disasters waiting to happen" published by the University of Colorado in 2004, along with a devastating hurricane striking New Orleans.

The most moisture Boulder had previously received on record in the month of September is 5.5 inches, in 1940, according to Camera weather historian Bill Callahan.

The Big Thompson flood of 1976 was considered between a 500-year and 1,000-year event. The disaster between Estes Park and Loveland killed 145 people and caused $41 million in damage after dumping 12 inches of rain in three hours. DailyCamera