Year’s snowpack looking weak

186 inches of snow recorded at Purgatory

This year’s below-average snowpack on Tuesday above Vallecito Reservoir means less moisture to fill the lake and less water for irrigation this summer. Enlarge photo

JERRY McBRIDE/Durango Herald

This year’s below-average snowpack on Tuesday above Vallecito Reservoir means less moisture to fill the lake and less water for irrigation this summer.

If storms don’t add to the current snowpack at Purgatory soon, winter 2012-13 could mark the fifth consecutive decline in total seasonal snowfall since 2007-08 when 290 inches fell.

In the preceding four years, Purgatory received respectively, 265, 233, 218 and 204 inches. So far this year, 186 inches have been recorded, 18 inches shy of the 2011-12 mark.

As March – traditionally the last month for significant snow – wanes, the chances of recovery aren’t promising.

A five-year downswing in snowfall, bears out the cyclical nature of snowfall at Purgatory, as an analysis by Fort Lewis College biology professor Heidi Steltzer graphically illustrates.

Steltzer, who has presented papers about the effects of early snowmelt on flowers in the San Juan Mountains at academic conferences, recently looked at the 47 seasons (1965-66 through 2011-12) of recorded snowfall at Purgatory from three perspectives.

She found:

No easily discernible pattern by scattering values for each of the 47 seasons along a line.

A five-year running average shows clear cyclical fluctuations. It was calculated this way: The first point plotted is the average for 1965-1969; the second, 1966-1970; the third, 1967-1971; and so on.

A mathematical formula based on the five-year running average shows that 16 percent less snow fell in 2011-12 than in 1965-66.

Overall, peak snowfalls in the 1990s were less than the peaks of the 1970s.

A bar graph that displays snowfall by decade – the 1960s and the decade that started in 2010 are incomplete, of course – shows more than anything else that the decade of the 1970s was the only period of extremely heavy snowfall.

The 2012-13 winter is shaping up as below average.

The snowpack in the San Juan Basin, which includes the drainages of the San Juan, Animas and Dolores rivers and their tributaries, stands at 84 percent of average, Dusty Crangle, assistant commissioner for the Animas and La Plata rivers at the state Division of Water Resources, said Tuesday.

Coincidentally, the snowpack stood at 84 percent of average in March 2012.

“We’re still struggling,” Crangle said.

Basin reservoirs show the effect of snow scarcity.

Jackson Gulch is at 14 percent of capacity; Lemon, 20 percent; Vallecito, 37 percent; McPhee, 50 percent; Navajo, 55 percent; and Lake Nighthorse, which is force fed from the Animas River, not runoff, 94 percent.

A storm expected to reach the San Juan Mountains tonight brings the best chance of snow for a week, Jim Daniels, a forecaster at the National Weather Service in Grand Junction, said Tuesday.

“You’ll see snow at 8,000 feet, but the heaviest accumulations will be above 9,000 feet,” Daniels said. “There a chance for precipitation Friday night and Saturday.”

Steltzer Enlarge photo


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