Coming cool weather notwithstanding, water-watchers in Montana are bracing for a crispy summer.
“Across most of the West, snowpack isn’t just low – it’s gone,” Natural Resources Conservation Service hydrologist David Garen said in a new report. “With some exceptions, this year’s snowmelt streamflow has already occurred.”
While western Montana retains some spring snow in the mountains, the rest of the West faces serious water deficits.
The Lake Powell Reservoir on the Colorado River is expected to get one-third of its normal snowmelt inflow this year. That reservoir supplies places like Las Vegas, Los Angeles and most of southern Arizona.
Virtually all water basins in Washington, Idaho and Oregon are reporting less than 50 percent of their current snow-water equivalent.
A cool, moist weather system is forecast to move across western Montana late Tuesday or Wednesday, and possibly drop rain through the rest of the week.
However, while it brings the possibility of snow at 6,000 feet of elevation, that won't do much to bolster the remaining snowfields.
The Columbia River basin snowpack was 61 percent of normal at the end of last week. The Kootenai River drainage fared worst, with only 42 percent of its annual average and 29 percent of what it had to work with last year.
The Flathead River drainage was in the best shape, with 69 percent of its snowpack remaining and 45 percent of 2014’s accumulation.
The Upper Clark Fork east of Missoula had 66 percent of its average annual accumulation and 41 percent of its 2014 mark. West of Missoula, the Lower Clark Fork got only 47 percent of its snow. That puts its accumulation at 29 percent of 2014’s total.
The Bitterroot River drainage got 59 percent of annual average and 31 percent compared to 2014.
Part of the problem for the Columbia River basin was the amount of rain that fell in late winter instead of snow. Compounded with a relatively dry April, the mountains don’t have much left to give.
“The ‘April showers bring May flowers’ thing – that really didn’t happen,” said Jeri Lynn Ward, a statistical assistant at the NRCS office in Bozeman. “We got two storms in April, one early, one in mid-month, and that was about it.”
Fortunately, many reservoirs enjoyed record-breaking snowfall last year, and they retain some of that storage. That should help irrigators and fisheries managers a little bit in the warmer months, but they aren’t likely to get any recharge help from this spring’s runoff.
Meanwhile, the U.S. Army Corps of Engineers reports that spring runoff into the Missouri River Basin was 1.5 million acre-feet of water above Sioux City, Iowa.
That’s 52 percent of normal. An acre-foot of water is the amount of water necessary to cover one acre of ground one foot deep – 326,000 gallons weighing about 2.7 million pounds.
The amount of water coming into the Missouri drainage in April was well below normal, due to lack of Great Plains snowpack especially in the Dakotas.
The total Missouri runoff for the year above Sioux City is forecast to be 19.3 million acre-feet – about 76 percent of the annual average of 25.2 million acre-feet.