Winter snowpack recedes earlier than usual in southern Colorado after rare, sudden and large melt

Southwestern Colorado is left with 6% of its peak snowpack earlier than usual this season in part because of a rare, sudden and large melt in late April.

Snow that gathers in Colorado’s mountains is a key water source for the state, and a fast, early spring runoff can mean less water for farmers, ranchers, ecosystems and others in late summer. While the snow in northern Colorado is just starting to melt, southern river basins saw their largest, early snowpack drop-off this season, compared to historical data.

For Ken Curtis, the only reason irrigators in Dolores and Montezuma counties haven’t been short on water for their farms and ranches is because the area’s reservoir, McPhee Reservoir, had water supplies left over from the above-average year in 2023.

“Because of the carryover, the impacts aren’t quite that crazy bad,” said Curtis, general manager of the Dolores Water Conservancy District. “If we hadn’t had that carryover, it would have been a terrible year.”

A terrible year like 2021, he added, when many irrigators who depend on water from McPhee only received 10% of their normal water supply.

The snowpack in the southwestern San Miguel-Dolores-Animas-San Juan combined basin peaked at about 18 inches April 2, then plummeted by 8 inches during the last half of April. It was the largest 14-day loss of snowpack before the end of April in this basin since the start of data collection in the 1980s, according to the Colorado Climate Center at Colorado State University.

The basin still held onto 1.1 inches of snow-water equivalent, the amount of liquid water in snow, as of Wednesday. Typically, the snowpack is about twice as high in late May, according to the Natural Resources Conservation Service.

“The Rio Grande and the southwest basins, the snow is pretty much gone, and it’s going to be gone within days to a week at this point,” said Russ Schumacher, the state climatologist and CSU professor.

The Upper Rio Grande Basin, which spans the central-southern part of the state including the San Luis Valley, had 0.1 inch of snow-water equivalent as of Wednesday, much less than its norm for late May, which is about 1.5 inches.

Eastern and northern basins, like the South Platte Basin which includes parts of Denver, have held onto their snowpack for slightly longer than usual. These basins have above-average snowpack for late May, ranging from 119% to 162% of the historic norm, as of Wednesday.

Colorado snowpack levels start to fall during spring runoff as of May 29, 2024. (Natural Resources Conservation Service, Contributed)

The April decline in the southwest was caused by warm and dry conditions and sublimation, when snow and ice change into water vapor in the atmosphere without first melting into liquid water. Dust that darkens snow and speeds snowmelt also played a role, Schumacher said.

The spring runoff is a little faster than usual in the southern basins, but it’s within the realm of normal, said Brian Domonkos, snow survey supervisor for the Natural Resources Conservation Service, which manages snow-measurement stations around the state.

“What we’re seeing right now is not something that I would be alarmed about,” Domonkos said.

Spring snowfall, storms and cooler temperatures have slowed the speed of snowmelt in some areas as well, he said.

In Durango, the Animas River’s flows were around 2,000 cubic feet per second Wednesday, lower than the late-May norm of 2,990 cfs.

When it comes to recreation, the lower flows might actually be a boon, said Ashleigh Tucker, who is planning a river sports event, Animas River Days, scheduled for June 1 and 2. Some races require participants to pass through hanging gates, moving both upstream and downstream through a whitewater park, she said.

“If the water’s super high, it makes it a lot harder to do. So as far as our events go, it’s a good level,” she said. “But there’s not much snow left, so that means we won’t really have much left for the rest of the year, which is kind of a bummer.”

She doesn’t expect the river’s slightly lower flows to impact attendance either: Only years with really low flows, about 1,000 cfs, have discouraged people from floating the Animas, she said.

Warm and dry conditions are likely to continue through June, then weather watchers will turn their gaze to the sky in July to watch for the monsoon season.

In the meantime, Curtis is watching inflow forecasts for McPhee Reservoir. The runoff has been lower than average so far, even after an average snowpack season, he said.

That means there might not be as much water left to carry over into 2025.

“The monsoons will have the next impact,” he said. “If you see everyone going on fire restrictions, you know the monsoons haven’t shown up.”

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