Below-average snowpack behind ‘troubling’ forecast
Water supply shortages are anticipated this summer in the Methow and Okanogan river basins, based on current snowpack measurements, soil conditions and weather predictions.
Water supply forecasts for the Upper Columbia basin, which includes the Methow River watershed, “range from troubling to dire,” said Jeff Marti, water resources planner for the Washington Department of Ecology in Olympia.
Although February was exceptionally cold and snowy in much of the state, north central Washington lost ground in terms of snowpack, Marti said.
“The rest of the state had huge snow. There’s a presumption of an awesome snow year. At the same time, your part of the state was missing out and gradually falling behind. You weren’t invited to the party,” said Marti.
The U.S. Drought Monitor has designated portions of Okanogan and Ferry counties as being in “moderate drought” due to an extended precipitation deficit, although snow remaining on the valley floor and surrounding mountains might seem to indicate otherwise in the Methow Valley.
Maia Bellon, director of Ecology, met recently with the state’s Executive Water Emergency Committee to discuss water supply conditions in Washington. “As unbelievable as it may seem, and despite the late season ‘snowpocalypse,’ parts of north central Washington may have water supply shortages and hardships this summer,” Bellon said in a tweet after the meeting.
“We’re monitoring the whole state very closely, but the Methow and Okanogan watersheds are our primary worry spots,” Marti said. “The Methow is probably the most snowpack-dependent watershed in the state in terms of how much of your water supply depends on snowpack.”
The Methow River, measured at the streamflow gauge at Pateros, is forecast to flow at about 75 percent of normal from April through September, according to the Natural Resources Conservation Service (NRCS). The Northwest River Forecast Center, operated by National Oceanic and Atmospheric Administration (NOAA) in Portland, predicts the Methow River streamflow to be only 63 percent of normal for April-September. The two agencies use different modeling to develop their forecasts.
Out of 71 years of records maintained by NOAA for the Methow River, that would make the coming summer the 65th-lowest streamflow, Marti said. “It would be the lowest in the past 14 years,” he said.
The lowest recorded streamflow for the Methow River was in 1977, and the next two lowest streamflows occurred in 2001 and 2005, Marti said.
February was no help
February’s frigid weather didn’t produce the precipitation in surrounding mountains that the Methow Valley needs to feed rivers and streams during the dry summer months. “February came on strong with very cold and snowy conditions statewide, however, the negative effects of the lowland snow outweighed the positive results of mountain accumulations,” said Scott Pattee, a water supply specialist with NRCS.
“One would think that mountain snowpack must have met or broken accumulation records. To the contrary, most of our SNOTEL [snowpack measurement] network were below the 50-percentile mark for the month,” Pattee said.
Precipitation in Twisp is only .6 inches below normal for the past 60 days, but it’s a different story in the mountains, Marti said.
“When you look at places higher up in the watershed there are some bigger anomalies,” Marti said. Upper Eight Mile Creek is 3–4 inches below normal for the past 60 days. For the current water year, which runs from October-September, precipitation at Harts Pass is almost 6 inches below normal, Rainy Pass is 15 inches below normal, and Swamp Creek is 8 inches below normal, Marti said.
A SNOTEL station at Rainy Pass, elevation 4,900 feet, recorded the snowpack this week at 69 percent of normal, Pattee said. Snowpack is measured in terms of how much water is contained in the snow.
While Harts Pass, one of the highest SNOTEL sites in the state, had a reading of about 95 percent of normal this week, snowpack readings are well below normal at most sites, Pattee said. “Conconully basin is only about 75 percent of normal.”
The snowpack deficit is exacerbated by low soil moisture throughout the watershed, Pattee said. “It’s a combination of things going on,” he said. “We had such a dry summer last year, and we ended the season with extremely dry soil moisture.” That means the dry soils will act like a sponge when spring snowmelt begins.
“If soils are fairly dry, the first meltwater will go straight into the soil instead of hitting streams,” Pattee said. Soil moisture records kept by NOAA for Rainy Pass since 2008 show this year to be the driest year, Marti said.
As in any year, the rate of spring snowmelt will impact summer water supplies. The weather forecast for the rest of the month calls for above-normal temperatures and below-normal precipitation. The forecast through May predicts warmer-than-normal temperatures with equal chances of above- or below-normal precipitation.
If summer streamflows in the Methow and Okanogan basins are as low as predicted, state officials may declare a drought. Under state statute, a “drought condition” means that the water supply for a geographical area or for a significant portion of a geographical area is below 75 percent of normal and the water shortage is likely to create undue hardships for various water uses and users.
“In low-water years, there are some folks [in the Methow Valley] with junior water rights that will be asked to stop diverting” water from rivers, Marti said. “For this year they can probably anticipate that happening again, and it might happen earlier than usual because we’ll have a small snowmelt season.”
Hardship created by drought, as defined by the state, includes economic and environmental losses for water users and uses, Marti said. That includes loss of crops or reduced crop yields, loss of fish populations, stranding of fish or blockages of fish passage in streams, and interruption of public drinking water, he said.
The state’s Executive Water Emergency Committee, comprised of several state agencies, evaluates hardship and can make a recommendation to the governor’s office and Ecology to issue a drought declaration, Marti said. The next meeting of the committee is March 27. The last statewide drought was in 2015, and junior water rights around the state were impacted.
The west slopes of the central and south Cascades benefitted most from the February snowstorms, bringing snowpack readings in those basins to near normal range. The Lower Snake River basin around Walla Walla had the highest snowpack reading at 103 percent of normal as of early this week.
Statewide, snowpack is at 87 percent of normal for this time of year, which ranks 11th-lowest for out of the past 30 years, according to Ecology. It is unlikely that the statewide snowpack will reach normal by early April, which is when snowpack usually peaks, although spring precipitation can continue to add water to the snowpack, Ecology said.