The Rocky Mountains have gotten near-average snow this year. So, why are forecasts for Lake Powell inflows so low?
Snowpack levels across the Upper Colorado River Basin are close to average for this time of year, but forecasters say that might not translate to a comfortable year for the Colorado River.
The amount of snow in the Upper Basin states — Colorado, New Mexico, Utah and Wyoming — doesn’t only determine ski conditions. In the spring, that snowpack will melt into the Colorado River and eventually spill into Lake Powell and Lake Mead, affecting the water supply for 40 million people across the West.
Cody Moser, senior hydrologist at the Colorado Basin River Forecast Center, said last week that “areas with better soil moisture conditions and better snowpack conditions are the areas where the forecasts are more favorable.”
Moser reported that snow levels above Lake Powell, which straddles Utah’s shared state line with Arizona, are 94% of average as of Jan. 1. (“Average,” in forecasting, refers to the average precipitation between 1991 and 2020.)
But forecasters currently predict that runoff into the reservoir between April and July will only be 81% of the thirty-year average. That’s a drop from the December forecast, which projected inflows of 92% of average.
The Lower Basin region — Arizona, California and Nevada — picked up almost zero measurable precipitation in December. Locals in St. George have also said they’re “nervous” about current drought conditions in southwest Utah.
“It’s been one of the driest starts to winter down there,” Moser said.
Utah’s soil moisture is also below average and worse than it was this time last year. That could impact how much water reaches the Colorado River and Lake Powell, since dry soil absorbs melting snow, leaving less water to run off mountains and into reservoirs this spring.
In terms of actual water, 81% of normal runoff into Lake Powell between April and July is 5.15 million acre-feet; the median runoff over the last thirty years has been 6.13 million acre-feet. An acre-foot is enough water to sustain two Utah households for a year, according to the Utah Division of Water Rights.
Lake Powell can hold more than 24 million acre-feet of water when full. But the second-largest reservoir in the U.S. peaked at just 42% full in July last year, up from peaking at 38% full in summer 2023.
