Where Did the Snow Go?

Pop Quiz: What factors influence streamflow?

A) Precipitation.         B) Snowpack. C) Soil Moisture. D) All of the above.

Answer: D. All of the above.

Snowpack peaked above normal this 2019-2020 season around much of Colorado, and when May started, snowpack statewide was nearly average, measuring at 94 percent of the median. But by June 1, snowpack across Colorado had declined rapidly and was 52 percent of the median (see figures below). With actual streamflows not as high as expected, many wondered “Where did the snow go?”

Almost all SNOTEL sites in Colorado saw a near normal timing of peak snowpack, and only 22 percent of SNOTEL sites saw peak snow water equivalent (SWE) values less than 90 percent of normal.

The snow melted, but stream flows didn’t increase as they normally would.

“Most streamflows peaked earlier than normal, and are now regressing to base flow,” writes Coyote Gulch regarding the National Oceanic and Atmospheric Administration's (NOAA) National Integrated Drought Information System (NIDIS) Drought and Water Assessment regarding Colorado. “Large reservoirs are still benefiting from 2019’s snowpack, but have seen far less inflow this year.”

The USDA’s Colorado Water Supply Outlook Report explains that the combination of an extremely dry summer 2019, fall 2019, and a dry 2020 spring reduced the snowmelt that made it into our streamflow. A lot of the snow sublimated due to warm temperatures and wind or melted and was absorbed into the ground due to seasons of dry conditions.

The takeaway here is that you can’t just monitor snowpack conditions to make predictions on streamflow.

Looking at these NRCS-USDA streamflow forecasts from May 2020 and June 2020 (below), you can see that even the experts’ projections on streamflow have changed drastically month over month (see the additional orange and red areas) and were impacted by May’s low precipitation and other factors.

Reservoir storage​, while 100% of average across the state, ranges from 62% of average in the Rio Grande to 115% of average in the Colorado and Yampa/White basins.