Snowpack/runoff news: Roaring Fork watershed early April accumulations looking good #COdrought #COflood


From the Glenwood Springs Post Independent (Will Grandbois):

he state as a whole is roughly 115 percent of normal, with a sub-par winter in the southern mountains (including the Rio Grande, Dolores and San Juan drainages) bringing the average down somewhat. Snow telemetry (SNOTEL) data provided by the Roaring Fork Conservancy shows a snow-water equivalent of 126 percent of normal in the Upper Colorado River Basin.

That’s the equivalent of about 20 inches of liquid water across the valley’s high country, well above peak snowpack in both 2012 and 2013, as well as the 30-year average for the region. It has been a good year for skiers, and it looks promising for healthy rivers and forests into the summer.

April is a key month in forecasting the year’s stream flow. Often it represents the peak snowpack for the Water Year, which runs October through September. This trend has been subverted in recent years. Early melting in 2012 signaled the beginning of one of the worst fire years in memory, while late runoff in 2013 was a small salvation in an otherwise below average year…

Dust storms, a frequent occurrence in recent years, also speed melting. The Colorado Dust-On-Snow Program recorded five such storms in the Rockies so far this year. That’s slightly less than 2012 and 2013, with a clean fall and an average March. April and May are big months for dust storms, so it’s too early to be sure how this year will compare on that metric.

“We’re now entering the thick of it,” Chris Landry, executive director of the Center for Snow and Avalanche Studies in Silverton, told the Aspen Times. He called the most recent dust storm on April 1 “a significant event,” but added that subsequent weather will dictate how this dust will play out.

So far, stream flows throughout the region are mostly above average. Discharge at Ruedi Reservoir has been set to 210 cubic feet per second, well over the 45-year average of 137 cfs. That might increase if snowpack continues to accumulate in coming weeks.

Meanwhile, many eyes are on the snowpack and the potential runoff problems in the flood affected areas along the Front Range. Here’s an report from Ryan Maye Handy writing for the Fort Collins Coloradoan. Here’s an excerpt:

Since September 2013 flooding swept across the Front Range, communities from Colorado Springs to Glen Haven have been preparing for the spring runoff, which could dislodge leftover flood debris and further damage areas torn apart by fall floodwaters. In a year with above-average snowpack, everyone from federal government conservationists to mountain fire departments are bracing for the worst.

But hydrologists and climatologists say there is no guarantee this year’s spring runoff will be as catastrophic as many anticipate. As with wildfire season, the intensity of spring runoff depends entirely on weather.

“Not all runoff seasons are created equal,” said Nolan Doesken, the state’s climatologist. “Just because you have a certain amount of snow, doesn’t mean you have a certain flooding potential. It all comes down to how snow melts.”[…]

Colorado hasn’t had this good of a snowpack — roughly 130 percent of normal — since 2011. Northern Colorado soils are still saturated after the fall floods; reservoirs are filled higher than normal, and rivers are running at twice or three times their average volume for early April.

River communities like Drake, Glen Haven, and parts of Estes Park are still scrambling to remove flood debris from the Big Thompson River’s path.

Since the September floods, places like Big Thompson Canyon have been in a race against time, trying to beat the arrival of spring runoff. The Colorado Department of Transportation hastily rebuilt the ravaged U.S. Highway 34, and has since been readying the canyon for snowmelt. Since January, the Natural Resources Conservation Service has poured all of its local energy into clearing debris or shoring up more than 44 weak points — or “exigent sites” — along the river…

Treste Huse, a hydrologist with the National Weather Service, worries that runoff will move sediment left behind by the September floods, or possibly cause land and rock slides along highways. River channels changed after the floods, and Northern Colorado residents could see water and dirt being poured into new places this spring.

But for Huse, like Doesken, this spring’s runoff potential depends on a few relatively unpredictable factors.

“It’s going to be dependent on future snowfall, how high stream levels are during the snowmelt, freezing and thawing in the mountains, future rainfall and the timing, and whether the rain falls on the snowpack,” she said.

The long and variable list of factors recently convinced Doesken that runoff might not be the catastrophe that everyone expects it to be. The state climatologist has changed his mind about this year’s snowmelt a few times–at first it wasn’t a big deal, then it was, and now the current weather pattern has him thinking Colorado could escape relatively unscathed.

If Colorado has a consistently warm spring, then the snowpack will slowly melt over time, as it did in 2011. Come summer, there will be little left once the temperatures rapidly rise, Doesken said.

On the other hand, a colder spring with a few lower-elevation snowstorms could create the opposite effect. Then, the snowpack would stay intact — even increase — until warmer temperatures suddenly hit, melting the snow rapidly. If Colorado gets a multi-day upslope winter storm that dumps moisture on the foothills, then Doesken says he will start to worry.

“The longer you push the snowmelt to when it (summer) starts, the closer to midsummer you are, it’s going to be really interesting,” he said. “It will all unfold day by day, week by week, over the course of the next six to seven weeks.”

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