It’s been a wet and cold winter in Idaho. What does that mean for snowpack?

BOISE (Idaho Statesman) — As spring nears, snowpack in most of Idaho is above normal, auguring higher-than-usual stream flows that could bring much of the state out of drought.

Conditions are “well above” normal in southern and eastern Idaho, Erin Whorton, a water supply specialist at the Natural Resources Conservation Service, told the Idaho Statesman.

Conditions in north Idaho, which had been less wet than the rest of the state, have also improved somewhat, Whorton said.

Through May, the National Weather Service’s Climate Prediction Center shows that much of the state will likely no longer be in drought for the first time in several years.

“Overall, the picture for drought improvement is really positive right now,” Whorton said.

Some river basins in or near the Treasure Valley — the Weiser, Payette, and Boise — have seen some snowpack reductions since last month but are still above normal for this time of year, Whorton said.

Soil remains dry across the state, however, and that can reduce the flow of melting snow into streams and reservoirs. The dryer the soil is, the more melting snow gets absorbed into the ground.

“It’s a little hard to know exactly how that’s going to play out, but it probably will have an impact on reducing runoff a little bit,” Whorton said. She added that the above-normal forecasts in most places may compensate for the dryer soils and still result in enough water to meet supply concerns.

The National Weather Service also predicts below-normal temperatures and above-normal precipitation for Idaho through the rest of March, meaning that more snowfall is likely on the way.

Snowpack generally peaks in Central Idaho in early-to-mid April, while southern Idaho tends to see its maximum snow levels in March, Whorton said.

HOW DO SCIENTISTS CALCULATE HOW MUCH SNOW HAS FALLEN?

Every month during the winter, government scientists across the Mountain West trek to sites in mountains and foothills, where they use a mix of high-tech automated monitoring equipment and old-fashioned measuring sticks to calculate how much snow has fallen, and how it will affect agriculture in the coming warm seasons.

In Idaho, scientists with the Natural Resources Conservation Service, a unit of the U.S. Department of Agriculture, snowshoe to about 129 sites in Idaho’s watersheds at the beginning of each month to measure the snow.

The most advanced locations are called SNOTEL sites, which include contraptions like snow pillows and precipitation sensors. Snow pillows are large, rubberish water-bed-looking pads embedded on the surface of the ground and filled with 150 gallons of water and antifreeze. When it snows, the weight of the snow settles on top of the pillow, and a sensor calculates its weight.

Scientists use that measurement to calculate the snow water equivalent, which is the amount of water contained in snow were it to melt. The precipitation sensor measures any precipitation, whether it falls as rain, snow, or graupel.

The SNOTEL sites also monitor temperature, wind speed and snow depth, broadcasting their automated results back to scientists’ computers every 15 minutes.

“In Idaho, about 75% of our water that ends up in the streams comes from our mountain snowpack each year,” Whorton said on a trip with a Statesman reporter and photographer to measure snow at Bogus Basin. “A very large portion of that goes towards agriculture and irrigated farming production in our state. So it’s really important for farmers to know how much water they have each year, so they can decide what crops they want to plant and grow.”

While the SNOTEL data is collected automatically, NRCS scientists also conduct snow courses once a month, which are carried out by plunging javelin-like metal poles into the snow at specific sites.

Each snow course involves multiple measurements at slightly different locations, which are then averaged to calculate the snowpack levels at each site.

While snow depth is an important measure for skiers, depth doesn’t reliably indicate how much water is in the snow. Surveyors bring special scales with them that are calibrated to capture the snow water equivalent.

Scientists have been taking “snow cores,” as they’re called, since the early 1900s, and measurements at a site at Bogus Basin have been collected since the 1940s.

Both manually through snow courses and automatically at SNOTEL sites, the NRCS takes snow measurements from about 260 locations across Idaho’s watersheds.