From The Fort Collins Coloradoan (Miles Blumhardt):
For the past month, Coloradans have been inundated with flash flood watches and warnings and a weather event — called a monsoon…
Neither flash floods nor the annual monsoon season have grabbed Colorado headlines the past several years because neither had much impact on the state.
That changed this year.
“This year is more normal of what we would expect from monsoon season compared to the past couple of years,” said Jennifer Stark, a meteorologist who manages the National Weather Service office in Boulder. “We are seeing bigger impacts, and people are really beginning to take notice because it is impacting their ability to recreate and move across the state and affecting homes.”
A series of events that has led to devastation started last year when the state experienced its worst wildfire season in its recorded 145-year history…
This summer, those burn scars, largely left denuded, have been continually saturated with abundant monsoonal moisture, resulting in large debris slides.
Those slides have continually closed Interstate 70 in Glenwood Canyon, which remains closed Monday due to what the Colorado Department of Transportation has called “extreme damage” to the major transportation corridor. It also resulted in the deaths of three people with a fourth still missing and six residences destroyed in the Poudre Canyon…
The Colorado Climate Center said the monsoon pattern is created by abundant moisture that builds in the atmosphere from the Gulf of Mexico and Pacific Ocean.
A shift in wind pattern results from a high pressure system with clockwise flow over the Rocky Mountains and low pressure near the Gulf of Mexico with a counterclockwise flow that settles over the region and squeezes moisture northward into the atmosphere.
In Colorado, the moisture is more prevalent on the Western Slope but can spill over the Continental Divide, which is happening this year.
This creates persistent afternoon thunderstorms that park over areas that can produce large amounts of rain, sometimes in a short period of time…
When that happens on burn scars, soil that repels water is washed down canyons, gullies and ravines that act as funnels of accumulating water. As it gains momentum, the slide brings with it large boulders and burned trees.
Stark said many of the state’s most devastating floods have taken place during the monsoon season, including the 1976 Big Thompson flood and 1997 Spring Creek flood in Fort Collins, both of which occurred in late July.