Fewer storms have coated Colorado mountains with red dust swirled from parched northern Arizona and southern Utah, which bodes well for water managers trying to predict how quickly the state’s snowpack will melt.

The lack of dust — at least on Colorado’s central and northern mountains — removes one capricious ingredient from the always tricky formula of forecasting runoff.

“Many factors impact the timing and flow of spring runoff, including soil moisture, snowpack, weather, dust on snow and solar radiation. Given all the variables that play a role, we’d hesitate to say that the lack of dust makes it easier to predict runoff,” Denver Water spokeswoman Stacy Chesney said. “The lack of dust on snow benefits water managers because, all other variables held constant, it means a slower and more predictable melting of the snowpack.”

It takes careful coordination to fill all 19 of Denver Water’s reservoirs, a balancing act that weighs a range of inflows, water rights, customer demands and projects, all influenced by dust, weather, snowpack, soil moisture and sunshine. Sometimes, water managers release water to make room for a surge of snowmelt.

Strong snowpacks in the South Platte Basin in recent years, combined with increased conservation by Front Range users in 2014, meant Denver Water diverted the least amount of Western Slope water through the Roberts Tunnel beneath Dillon Reservoir since it opened in 1963. Last year, also one of very low dust, Denver Water diverted the second-least amount since the tunnel opened.

Snow researchers in southern Colorado for 13 years have studied the red dust swirled onto the snowpack from the Colorado Plateau.

The Colorado Dust on Snow Program was launched up Red Mountain Pass outside Silverton in 2003, where researchers with the Center for Snow and Avalanche Studies had started noting stronger dust storms laminating the San Juans in a pink patina of sun-sucking dust. When the spring sun began melting the snowpack, those dust layers would collapse on top of one another, creating a dark blanket that absorbed sunshine and hastened snowmelt from a slow trickle into a sudden surge.

By 2008, the dust-on-snow researchers were studying snowpacks atop a dozen Colorado mountain passes, compiling data that now are essential tools for water managers tasked with corralling as much of Colorado’s own water before it rushes downstream to other users.

They measured three dust storms the first year. There have been big years, with as many as 12 dust events: 2008-09 and 2011-12. And there were years with only three: 2003-04 and 2014-15.

This winter was about average, with six dust events and most of them relatively small. Most interesting this year was the lack of dust accumulation on Berthoud, Loveland and Rabbit Ears passes.

A slight bit of dust fell on Hoosier Pass, but the central mountains largely escaped without much airborne dirt this year. And each of the dirt-flinging storms that blanketed southern Colorado were followed by snow that quickly covered the sandy bits of Utah and Arizona, preventing an early melt. Those layers are starting to get exposed on southern aspects with this week’s warm weather.

“We are seeing an uptick on the stream discharge gauges,” said Jeff Derry, the new boss of the Center for Snow and Avalanche Studies. “Central Colorado is doing great so far. Seems like the southern half of the state is bearing the brunt of this year’s dust. We were really surprised to see nothing on Rabbit Ears and Berthoud this year.”

Still, water watchers such as the Colorado River Water Conservation District are hardly kicking back. The recent storms bolstered Colorado’s snowpack, which in April improved 7 percent, marking the first month-over-month increase in 2016. The Natural Resources Conservation Service on Friday announced that April snowfall pushed the state’s overall snowpack to 110 percent of normal, with year-to-date precipitation hitting 100 percent of normal.

But even with the lack of dust and healthy snowpacks across the state hovering a little above the long-term average, managers are bracing for the typical dryness that follows an extra-wet El Niño weather pattern.

“Colorado is in a time of plenty,” district manager Eric Kuhn said.

But that barely translates to good news for Lake Powell, which is dangerously low and nearing a drop below the level of the power generators on Glen Canyon Dam. Lake Mead, feeding the extraordinarily thirsty Las Vegas area, is equally low, threatening to drop below the level of intake straws that sate southern Nevada.

Even with healthy conditions up high on the Colorado River, demand continues to outpace supply in the lower river basin, Kuhn said. So he’s among many managers planning widespread conservation measures.

“It’s time to think about phasing out of our time of plenty,” Kuhn said.

Storms forecast for the coming days are good news. New snow expected across the high country should cover the dust layers in the southern mountains, slowing the inevitable runoff.

Yet the dust season is not over. Utah and Arizona typically share the largest portion of their desert in April and May.

“A lot of people are praying for what happened last year,” Derry said, noting how that exceptionally wet spring bolstered emaciated snowpacks to above average across the state. “The forecast looks good. We’ll see if we get that miracle May two years in a row.”

Jason Blevins: 303-954-1374, jblevins@denverpost.com or @jasonblevins