Idaho’s water supply for agriculture looks good for those areas that have reservoirs to carry over the bounty from the 2017 season.
But as the closure of Bogus Basin skiing this week shows, snowfall this winter is starting off slow, leaving places like Weiser and Owyhee County anxious. Long-term trends still point to a colder, wetter winter later, and whitewater rafters and late-season skiers may still be rewarded.
A third of what hydrologists say is the normal precipitation over the last 30 years fell in December across Idaho’s west-central and central mountains. Those include the Boise River watershed. Still, North Idaho had normal precipitation and the Upper Snake near the Wyoming border had 114 percent of normal snowpack, according to the U.S. Natural Resources Conservation Service.
“The good news for water users is that last year’s high snowpacks and runoff primed the hydrologic system and has kept rivers and springs flowing above average well into this fall and early winter,” Ron Abramovich, an NRCS water supply specialist in Boise, said in a press release.
Compare things to last year, when snowpack at this point in the Boise basin was slightly above normal. At the time, that didn’t worry the dam and river managers who seek to balance Idaho’s reservoirs: capturing enough for the irrigation season, while keeping enough space available to handle later snowmelt from the mountains. Even at the end of January, the runoff — while higher than normal — did not look like a serious issue.
But beginning in the early days of February and continuing through a record runoff in March, the mountains filled with snow and the runoff across the Northwest threatened serious flooding across the region. Nowhere was it closer than in Boise.
Managers saw the highest inflows into our reservoir system since Arrowrock was built. The more than 3 million acre-feet of water that came in could have filled it 2.4 times by now.
The Boise River ran at flood stage from March 7 to June 15 — 100 days of anxiety for its neighbors, a record. Major damage was averted, but millions will be spent to restore the Greenbelt, which still has sections closed.
Hydrologists are watching the large-scale climate patterns this season. They suggest a shift toward cooler temperatures and increased precipitation in the coming months. Current weather patterns are bringing lots of snow and very cold temperatures to the Canadian border, from Washington to the Great Lakes and beyond. La Nina conditions, a slight cooling in the South Pacific, are expected to bring wetter conditions in the second half of the winter to the Pacific Northwest.
California and the southwest U.S. are generally seeing low snowpacks and further dry conditions like those that brought the record fire season in southern California this year. Those conditions reach into southern Idaho, and where the jet stream brings more storms and moisture to will determine just where we will be by April.
“We’re not quite halfway through the season, and a lot could change.” Abramovich said.