This article was published on: 10/20/18 12:00 AM
As winter approaches, the evidence suggesting another low-snow year for Central Oregon and much of the Pacific Northwest is mounting.
The National Oceanic and Atmospheric Administration Climate Prediction Center’s most recent update to the winter outlook notes a 70 percent to 75 percent chance of a weak El Niño weather pattern developing over the Pacific Ocean in the next couple of months. For much of Oregon, this may mean warmer temperatures and less snowfall.
“It doesn’t mean you’re not going to see winter; it just means you’re going to see temperatures that are on average higher than normal,” said Mike Halpert, deputy director of the Climate Prediction Center.
El Niño is the name given to a climate pattern that involves warmer-than-normal sea water and atmospheric changes in the central Pacific Ocean. El Niño patterns affect regions of North America in different ways, although they’re known for bringing less snow than usual to Central Oregon, said Marilyn Lohmann, hydrologist for the National Weather Service’s Pendleton office.
In a region mired in drought after a series of low-snow winters, another dry, warm winter could exacerbate problems throughout the Deschutes River Basin for farmers and fish.
“I think there’s some anxious folks, to be honest,” said Mike Britton, general manager of North Unit Irrigation District.
Halpert said the Climate Prediction Center, which provides data and predictions designed to help communities prepare for climate risks, looks at a variety of indicators when predicting an El Niño event, including surface and subsurface water temperatures and the location of rainfall in the tropics. While the rainfall location hasn’t yet squared with what the center would expect during an El Niño year, the water temperature is approaching the threshold that would suggest a weak El Niño, he said.
The Climate Prediction Center is planning to update its El Niño prediction in mid-November, when some of the climate indicators will be more settled, Halpert said.
If it does come to fruition, there’s no telling precisely how an El Niño pattern would affect Central Oregon. History suggests it will cause a milder winter than normal.
Bend receives an average of about 31 inches of snow between October and April, Lohmann said. During 11 years where a weak El Niño system was present, the city averaged 24.2 inches, about 22 percent less than a typical winter.
Lohmann added that snowfall in the 11 years the weather service examined varied dramatically. Totals ranged from 4.8 inches to 49 inches during weak El Niño years.
The last weak El Niño, which occurred during the 2014-15 winter, was one of Central Oregon’s driest winters to date, with just 8 inches of snow falling in Bend all year, virtually none of which lasted until spring, Lohmann said. By contrast, the El Niño pattern that occurred the following winter was much stronger globally, although it brought a roughly average amount of snow to Bend and Central Oregon.
“Each one is different, and there’s a lot of other atmospheric things in play, as well,” Lohmann said.
The Climate Prediction Center is forecasting warmer-than-usual weather in Oregon and Washington, with a roughly equal chance of being drier-than-normal or wetter-than-normal, Halpert said.
Central Oregon’s snowpack is susceptible to small fluctuations in temperature, which can make the difference between precipitation falling as rain instead of snow, Lohmann said.
“It just takes a few degrees, especially in the mountains,” she said.
Central Oregon saw significantly less snow than usual last winter and spring, which left the region in bad shape once irrigation season began. Wickiup Reservoir, Central Oregon’s largest, reached its lowest level in 60 years just months after filling to capacity, thanks to irrigation demand and a lack of precipitation throughout the year.
Water levels at several large reservoirs in the Crooked River Basin also dropped well below their seasonal averages.
North Unit Irrigation District, which relies heavily on Wickiup Reservoir, sets allotment totals for farmers during dry years, but still left Wickiup at 1 percent full by the end of irrigation season, Britton said. If there’s another dry year, Britton said, more farmers could leave portions of their fields unsown to conserve water.
“We’re starting to see a lot of fallow ground,” Britton said.
A light snowpack could hurt fish living in Central Oregon’s rivers. Kimberley Priestley, senior policy analyst for WaterWatch of Oregon, said the Crooked River is more snow-driven than the Deschutes, making it more vulnerable to a single dry winter. Low levels on the Crooked River could cause problems for redband trout, steelhead and other species living in the river.
— Reporter: 541-617-7818, shamway@bendbulletin.com