Scientists say the storm on March 6 caused unprecedented melting. The dust-on-snow show came during five hours of wind that averaged 34 miles per hour and gusted up to 57 mph on ridgelines at the Reynolds Creek Experimental Watershed in the northern Owyhee Mountains.
Hydrologists at the U.S. Department of Agriculture research area then observed accelerated melting from March 10 to March 16, when a new dusting of snow covered the layer of dirty snow.
"Nobody on our staff has ever witnessed anything similar," said research hydrologist Adam Winstral.
Snow surveyors with the Natural Resources Conservation Service said they saw dust on snowpacks as far east as the upper Mores Creek watershed near Idaho City.
"Because it's been so dry in the valleys in Oregon and Nevada, the wind picked the dust up and carried it here," said Ron Abramovich, Idaho NRCS Water Supply Specialist.
Reynolds Creek scientists studying snowmelt rates have been working with hydrologists in Colorado, who have observed dust storms speed up snowmelt by several weeks, with shifts in the peaks of runoff.
Abramovich said the runoff in the Owyhee River peaked on March 16, a week earlier than the norm.
What's at work? Dust reduces the snow's ability to reflect sunlight and it also absorbs solar radiation, Abramovich said.
His staff has removed 3-inch core samples of snow that leave as much as a half-inch plug of dust behind.
Returning a month later, the snow melted a ring around that dark spot that was 3 feet wide by 2 feet deep, he said.
"That's just one spot," Abramovich said. "When you spread this much dust over the watershed, you know there are impacts."
Southern Idaho precipitation was down dramatically this winter. Federal snowpack researchers have updated the averages they use as comparison data - the past 30 years, which were relatively dry - and that makes the snowpack this year look a little better.
In the Boise River basin, for instance, precipitation is running at 84 percent of average. In the Owyhee drainage, it is 87 percent.
In eastern Idaho and parts of Wyoming, Upper Snake River precipitation is at 86 percent of average. Henry's Fork is at 91 percent and the Willow Creek and Blackfoot drainages are at 89 percent.
Elsewhere, things look better. Northern Idaho precipitation is at 100 percent and the Salmon River at 95 percent of average precipitation since Oct. 1, according to the NRCS.
Scientists are careful not to speculate about what could be causing the shifts in weather. They generally say that climate change is giving Idaho warmer winters and hotter summers that fuel bigger fires - which in turn leave the deserts with less native grasses to hold the soil.
Dust storms were reported in Oregon and Nevada last year after major wildfires. The Holloway Fire started Aug. 5 along the Oregon-Nevada border and quickly grew to 461,000 acres. The Long Draw Fire burned 582,000 acres in July.
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