Colorado's snowpack began melting quickly this spring because of warm, dry temperatures in early April, according to the USDA's Natural Resource Conservation Service (NRCS), which tracks snowpack and reservoir levels throughout the state.
Weather turned wetter and cooler throughout the mountains in late April, halting, and in some cases even reversing, the melt trend. Statistics from the latest NRCS surveys show snowpack is below average in all of the state's major river basins. Snowpack in the Blue River Basin in Summit County is 70 percent of average and 65 percent of last year's snowpack. At one NRCS survey site in the lower Snake River, snowpack is at only 7 percent of average.
“We did have some fairly warm temperatures earlier in April when melting was going on across the state for two weeks pretty steadily,” said NRCS snow survey supervisor Mike Gillespie. “We saw a lot of lower-elevation sites melting out at that time.”
Colorado's statewide snowpack decreased to the lowest reading of the season on May 1 at only 78 percent of average.
“For the most part, any gains we saw during the last week of April were far surpassed by the melt we saw earlier in the month,” said Allen Green, state conservationist with the NRCS.
Across northern Colorado, where the lowest snowpack readings have been recorded all season, snowpack declines were minimal in April. Basins showing the greatest declines during April included the Gunnison, Arkansas, Rio Grande and the combined San Juan, Animas, Dolores and San Miguel basins.
Monthly precipitation data collected at automated NRCS sites across higher elevations showed an above-average total for April across the Gunnison, Colorado, South Platte, Yampa, White and North Platte basins. For most of the region, April's above-average precipitation breaks a five-month-long dry period where the NRCS recorded below-average moisture. Statewide precipitation during April was 117 percent of average and was the first month of above-average precipitation recorded for the state since December 2009.
Late-season improvements in the snowpack will have positive impacts on this summer's runoff and water supplies, according to Green. However, forecasts of seasonal runoff volumes will remain below average, and in many locations across northern Colorado, this year's summer water supplies continue to be forecast at well below average volumes.
Inflow into Dillon Reservoir is expected to be 73 percent of average during the April-July period. Inflows into Green Mountain Reservoir and Williams Fork Reservoir are projected to be 75 percent of average and 78 percent of average, respectively.
“Reservoir stores are now in good shape, but they'll probably drop quite a bit as we go into the fall. They will be put to use in late summer to make up for these deficits in natural flows,” Gillespie said. “Without having much of a cushion, it increases the need for a good year next year.”