Snowpack Update

Snow covers the peaks above the Summit at Snoqualmie Pass in January 2018. The snowpack is currently over 100 percent of average and is concentrated at higher elevations.

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As winter comes to a close and spring fast approaches, the available water for this season’s irrigation in the upper Yakima Basin looks promising for local producers.

According to presentation materials from Thursday’s Bureau of Reclamation river operations meeting, Yakima Basin precipitation is at 114.9% of average from October to February, while as of March 1 the Yakima Basin snow water equivalent is at 103% of average. The total system storage volume for Yakima Basin reservoirs is at 107-percent of average, currently at 626,385 acre-feet. At this time last year, that number was 504,263 acre-feet.

The bureau also released its first total water supply available forecast for the season, and it showed that if the current forecast persists, the prorationing for junior water rights holders will be at 95-percent.

In the presentation material, the Climate Prediction Center at the National Oceanic and Atmospheric Administration states that March shows a below normal prediction for precipitation, with spring showing an equal chance and summer predicted to be below normal.

“We will stay wet with some decent breaks too,” Meteorologist Phil Volker of Extended Range Forecasting said in the release. “These late season upper lows will bring decent snow and rain to the region but will also keep snow levels very low for this time of year. This helps to set up a good spring freshet around the region, leading to good stream flows during late winter as we head into spring/summer.”

“Things are looking good,” Bureau Hydrologist Chris Lynch said. “For the water year, we’re still at about 114%. On the first, we were at about 115%. We’re above average for the water year.”

Lynch pointed out that the last two months have been dramatically above average for precipitation, with January coming in at 171% and February clocking 162% of average.

“It really helped us make up for a low November, which was only 25% of average and had a lot of us starting to worry as we went through mid-December and didn’t have too much rain,” he said. “Then it started to come at us around Dec. 17, and from then on it was wet.”

Although the snowpack numbers are looking positive, Lynch pointed out that the gauging sites are at high elevations, and that low-elevation snow is coming in at below average.

“That single number that you see may be a little optimistic for the snow coverage,” he said. “The gauges are a little biased for the higher stuff. That should mean that we should be OK at our reservoirs. Our inflows to our reservoirs should be good and that number should represent them well, but the natural flows that depend on lower elevation snow, like below 3,000 feet, that snow that helps early season runoff is behind. It’s not your typical distribution of snow this year.”

Lynch said that normally it is a positive thing to have the snowpack concentrated at higher elevations, as it tends to last longer into the irrigation season as lower level supplies melt off in higher temperatures. If the lower elevations receive precipitation during spring, he said it could make up for the lack of current supply in those areas.

“It might affect refill of reservoirs early in the season if it persists in the drier conditions and with this lower-level snowpack being below average,” he said. “It could cause us to release water for some early season demands more than normal. The thought then is that might not fill as quickly because we might have to make some releases. It sort of depends on how the melt and the timing of it works out.”

Looking forward, Lynch said precipitation and temperatures will affect both the demand for water and the rate at which existing snow melts. Regarding prorationing, he said things will inevitably change as the season continues, and the current 95% number will most likely fluctuate in one direction or the other.

“It will depend on a lot of the conditions from here out, both up high and down low,” he said. “The whole package, so to speak. This is just the earliest of our forecasts, and things do change as we’ve seen in the past. It can go both ways. We’ve had really good dramatic recoveries in the spring as well.”

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