Parts of northern Colorado that were swamped by massive flooding last September now face the potential of additional flooding this spring.
According to a spring flood outlook issued by the National Weather Service forecast office in Boulder, Colo. (NWS-Boulder), the risk of at least minor flooding is high in the Big Thompson River and St. Vrain Creek drainage basins, including Boulder and Estes Park. A moderate risk of at least minor flooding is in play in the Cache La Poudre River basin, including Ft. Collins and Greeley.
One reason for the elevated risk is a near-record snowpack for early March, from 150-200 percent of average in parts of the Colorado high country from western Larimer County northwest of Ft. Collins to the mountains west of Boulder.
Average monthly snow from March through May in Estes Park, Colo. (Data: NWS-Boulder)
Of course, as with all spring flooding, snowmelt is only one factor. The following would enhance the threat of spring flooding:
- Heavy rain
- Additional heavy snow
- Quick, intense warm spells
Spring is notorious for heavy, wet snow events along the Front Range, foothills and high country of Colorado. As you can see in the graphic at right, over four feet of snow is the average in Estes Park, Colo. from March through May.
The September 2013 floods introduced some further threats this spring for flood-ravaged areas.
First, rockslides and debris flows may be more numerous during times of either heavy and/or persistent rain, as last September's torrential rain destabilized hillsides and slopes, according to NWS-Boulder.
Furthermore, water may back up in streams containing silt or debris from the September flood, creating additional flooding, somewhat similar to an ice jam.
In short, the ideal scenario to limit spring flooding would be a chilly, dry spring, allowing a more controlled snowmelt. A May foothills/mountains heavy snow event, followed by a quick warm-up, would be a more ominous flooding scenario.
MORE: The Colorado Flood of Sep. 2013
Victims of last week's devastating floods retrieve belongings outside a home near the East Platte River east of Greeley, Colo., Tuesday, Sept. 17, 2013. The area's broad agricultural flatlands were especially hard hit by the high water. (AP Photo/John Wark)