Snowpack jumps in a month, runoff forecast goes with it

Already several things stand out about this winter’s snowpack.

First, it was late arriving, with most areas reporting dry conditions up through late November.

Second, once it started, it came in a hurry, with snow levels going from barely there in early December to waist-deep a month later.

And third but certainly not the last we’ll hear from this winter, the runoff is forecast to be one of the highest in a decade

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In roughly two weeks (Jan. 1-17), the projected inflow to Blue Mesa Reservoir leaped by 340,000 acre feet.

“In early December, there was maybe 6 inches of snow at my house in Gunnison,” recalled Michael Dale Thursday’s during the Bureau of Reclamation’s quarterly Aspinall Unit Operations meeting in Montrose. “Now, it’s this high,” holding his hand a bit above his waist. “We’re about to start digging tunnels.”

While skiers focus on snow depth, water managers refer to the water in that snow, or snow water equivalent. The total inches of snow matter only in the sense of how much water that snow may release in the spring.

That said, remote-monitoring precipitation gauges across the Upper Colorado River Basin showed large jumps in late December and by the end of the month, the entire region (except for the Little Snake River on the Colorado-Wyoming border) was at least 129 percent of long-term average.

Local Bureau of Reclamation officials said Thursday that nearly all the snow monitoring sites across the Upper Colorado River Basin saw 150-percent of their average precipitation during December.

“We thought December was a really good month and then we came into January,” said Erik Knight, hydrologist for the BOR West Region office in Grand Junction.

The Upper Gunnison Basin snowpack went from 69 percent of average on Dec. 1 to 119 percent on Dec. 31 and jumped to 171 percent of average by Jan 13.

“Most of the sites registered 200 percent of increase in the first 17 days of the month,” Knight said.

Knight showed a graph illustrating how many days it took five snow-monitoring sites across the upper Gunnison Basin to receive their monthly average snowfall. While most sites needed more than two weeks in December (and most of that coming in the last two weeks), none took more than 10 days (and one site took only six) to reach their January average.

And then they all doubled that amount in another 10 days or less.

“And we still have nearly half of January to go,” Knight reminded the audience.

The January runoff forecast says Blue Mesa may see 928,000 acre feet of inflow, about 136 percent of long-term average.

Despite the information available, risking a runoff forecast four months out always is thin ice.

Many factors – dry soils, warm and/or windy conditions, abrupt changes in weather pattern – can affect runoff.

“We have a long way to go,” Knight said. “The forecast is bound to change and it can go either way.”

But already dams across the state are expected to fill, he said.

“We are way ahead of schedule.”

 

 

 

 

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