Willow Creek inflow record shattered, with more to come

After 57 years of tracking Willow Creek Reservoir stats, we've now hit an amazing new inflow record.

Some background: in the Western U.S., April through July are considered the snowmelt months, so official streamflow forecasts (and thus runoff records) are based on that four-month period.


Willow Creek Reservoir

Until now, Willow Creek Reservoir's inflow record was in 1986, when the April through July runoff totaled 85,600 acre feet, which is 168 percent of the official average of 50,800 acre feet. That sounded like a lot until yesterday, when we tabulated the inflow since April 1 as 87,100 acre feet. And we still have six weeks to go! 

Our latest forecast anticipated a total of 110,000 acre feet of inflow to Willow Creek by July 31. If it materializes, this would be 216 percent of the official average. And the Colorado Basin River Forecast Center expects even more than we do. 

The peak inflow rate (in daily average) this year was 1,652 cfs on June 7. This wasn't quite a record, but anything more than 1,500 cfs is notable for Willow Creek. This date of peak inflow was about two weeks later than usual (about May 24); late peaks often come hand-in-hand with larger-than-normal snowpacks.

This staggering runoff quantity raises questions about what kind of runoff we should expect from neighboring watersheds - especially above Lake Granby. While we don't expect as high an inflow to Granby, our latest forecast anticipates 175 percent of average, which would be another one for the record books.

It's disconcerting to drive past Granby, which is 20 feet below full, and see the surrounding dry sagebrush - if you know how high snowpack is in Rocky Mountain National Park and along the Gore Range.

That snowpack may seem remote and unassuming, but looks are deceiving. Stay tuned.