Boulder County avoided the first wave of flash flooding Tuesday, but forecasts still call for widespread showers and thunderstorms that could produce 1 to 2 inches of rain quickly, with the potential for heavy flooding in some areas.

Though Boulder remains mostly dry as of 4 p.m., several inches of rain have already hit parts of the Front Range -- and quickly. The National Weather Service reported parts of western Weld County saw 4 inches fall in just 90 minutes, while parts of Larimer County and Denver have already seen street flooding. 

Should showers reach Boulder, the spots under the highest risk for flash flooding include low-lying areas, creeks and streams is, while rock or mud slides are possible in areas where the terrain is unstable.

Any flood potential in the Boulder area is viewed with perhaps more worry than it might have been this time 12 months ago, given the historic rains and devastating high water that ravaged much of Boulder County and Colorado's northern Front Range last September.

"It's certainly concerning," meteorologist Matt Kelsch said, of the forecast. "It doesn't look as potent as then, if you are looking at comparing, but this is something that we should be concerned about."

That concern remains in effect until 6 p.m. Wednesday, when the National Weather Service's most recent flash flood watch for areas including Boulder County is set to expire.


"We do have a higher sense of urgency, which relates to our watching to see how it develops," said Mike Chard, Director of the Boulder Office of Emergency Management. "Depending on how the low (pressure) sets up and how the upslope gets positioned, we will be on that all day, and if we see things that alert us to elevate our response, we will implement our severe weather protocol."


Chard noted that the September storm did not show its true dimensions until after dark on Sept. 11, and that the weather today, if it turns bad, could also be an event that makes its greatest impact after nightfall.

"Our goal is to have everyone current on what's happening, and knowing where to find sources of information, so as this goes into the evening, people are prepared and know what they're facing, when they go to bed," Chard said.

In addition following the National Weather Service, Boulder's emergency management personnel also utilize data and bulletins from the Urban Drainage and Flood Control District, based in Denver, which serves 40 different governmental entities on the Front Range.

"I would say we're probably at the point of being equally concerned as we are any other day at this time of year," said Paul Hindman, the district's executive director. "As the storms come through here, they hit basin by basin, and with our flood warning project, we watch it every day. But, it's not like we're ramped up (for Tuesday), let's put it that way."

Catching forecasters' attention on Monday was what they refer to as the "available" moisture in the atmosphere, a reference to the moisture that can, conditions permitting, be converted into rainfall on the ground, and does not follow a one-to-one relationship.

For example, on Sept. 11 last year, as the historic storm's fury was making itself felt, the available water vapor in the atmosphere was measured at 1.4 inches. On Monday afternoon, according to NWS meteorologist Bernie Meier, it was 1.03 inches.

"That's unusually high but not a record high," said Meier, who added it is a "top-25" reading for the month of July. "And it might be a little higher tomorrow. I know an inch doesn't sound like a lot, but for Colorado that's a lot of water in the atmosphere, meaning, it's right over your head."

Hindman, at the Urban Drainage and Flood Control District, stressed vigilance.

And, he said, "We like to tell people if a flood does happen, to make sure that you get out of the way of the flood water. Do not drive or walk or in any manner go into floodwaters. That's where most of the lives are lost."
