The U.S. Bureau of Reclamation forecasts Yakima Basin irrigators with junior water-rights will receive 48% of their full allotments and could receive far less if the spring turns warm and dry.

The five reservoirs that store water to irrigate 464,000 acres in south-central Washington hold about one-third as much water as normal for early March, the third lowest-level since 1971, the bureau reported March 6.

Snow will melt into the reservoirs, but the snowpack is only 78% of normal. “It’s a rough year,” Reclamation civil engineer Kain Shaffer said. “I would hope for a miracle March and a big winter event.”

Reclamation predicted the total water supply will be 69% of average. Senior water-right holders will receive their full allotments, leaving what’s left for junior water-right holders.

Depending on the weather in the coming weeks, junior water-right allotments could rise to 78%, but it also could drop to as low as 20%, the bureau projected.

The Yakima Basin suffered a water shortage last year, with junior water-right holders receiving 52% of their normal allotments.

The Roza Irrigation District, the largest district affected by the water shortage, has prepared plans to operate with a water supply as low as 40% of normal, according to an email from district manager Scott Revell to irrigators.

The district likely will stop delivering water for at least 10 days when water rationing begins, according to Revell.

Early season shutdowns extend the irrigation season in the fall. The district also plans to lease senior water rights.

“If you have land that can be fallowed, you should take a hard look at doing so this year,” Revell wrote.

Wine grape grower Jim Willard, on the Roza board, said he will fallow some land and expects other farmers will too. The district has improved its delivery system to conserve water, but the low end of the bureau’s outlook is concerning, he said.

“If the Roza gets 70% percent, we can manage getting enough water to the growers,” he said. “Below 40%, it’s going to be a real challenge.”

Reservoirs were low at the end of the irrigation season and have not recovered. Most reservoirs are unlikely to fill, according to the bureau.

A La Nina that formed over the winter has been weak. A La Nina usually creates conditions for snow and rain. Rainfall at the reservoirs has been 76% of average since Oct. 1.

The Climate Prediction Center forecasts that March, April and May will be colder and wetter than normal in Washington.

The Bureau of Reclamation plans to update its forecast April 3. Water rationing usually begins in late spring.