Just about every time Colorado State Climatologist Nolan Doesken rattled off recent precipitation amounts from various foothills communities, adjectives like “bizarre” and “incredible” shortly followed.
Doesken said that in “wet” Septembers, Front Range cities typically see 3 inches of precipitation during the month, and maybe as much as 5 inches in “really wet” years.
But during the seven-day stretch from Sept. 8 through Sept. 15 morning, some parts of Aurora, Colo., saw as much as 15 inches of rain.
“It was just remarkable,” he said Sunday afternoon, noting his totals didn’t take into account the rainfall that was still dumping on the region that day.
In Boulder, measurements ranged from about 15-18 inches for the week, Doesken said.
Fort Collins, Colo., saw 4-5 inches.
Parts of southern Weld County experienced 7-8 inches.
“That all eventually heads your way,” Doesken said of the northeast Colorado, where the floodwaters from South Platte, St. Vrain, Big Thompson and Cache La Poudre rivers all merged to inundate farm and ranch land along the rivers.
“What happened was incredibly unusual,” he continued. “Based on historic data, we’ve seen isolated events in the past where we had these huge amounts of rain, even more than we saw this past week ... but only in isolated areas. To see such huge, widespread precipitation amounts taking place is something extraordinary.”
Doesken said the culprit is the combination of unseasonably warm temperatures in early September, along with a particularly concentrated moist air mass and light winds that pushed that mass up high — and left it there to dump a year’s worth of rain in just days in some parts of the region.
“There are still some things that don’t make sense,” Doesken said. “Why does Aurora and Boulder get 15 inches of rain ... and some parts of Denver only get less than 2 inches?”
Also a mystery is where the 2013 flood ranks historically.
“We’re not to a point where we can call it a 100-year flood, or 500-year flood,” he said. “What we do know is that it was very unusual.”
Among the worst Colorado floods, according to Colorado Climate Center data, occurred in May 1904, October 1911, June 1921, May 1935, September 1938, May 1955, June 1965, May 1969, October 1970, July 1976, July 1981, and the Spring Creek Flood of July 1997 that ravaged Fort Collins and the CSU campus.
Officials with the Colorado Climate Center and Colorado State University are encouraging residents to help climate experts answer questions about the recent floods.
They’re asking that rain gauge measurements, personal anecdotes about the storm and photos that might help document this storm be sent to firstname.lastname@example.org. ❖