Keechelus Lake and four other Cascade Mountain reservoirs serve the farm-rich Yakima Basin.

The U.S. Bureau of Reclamation predicted Thursday that Yakima Basin irrigators in southcentral Washington will receive full or nearly full water allotments between April 1 and Sept. 30 from federal reservoirs.

Irrigators with senior water rights are expected to get 100%, while junior water right holders are forecast to get 96%. More snow in March would firm up or improve the outlook, the bureau’s river operations engineer, Chris Lynch, said.

“I think we’re actually in a good situation,” he said. “We’re hoping for at least a normal spring to build up our snowpack.”

The March water-supply forecast was the first of the year and will be updated monthly by the bureau, which manages five major reservoirs in the basin. The reservoirs supply water to irrigate about 464,000 acres on both sides of the Yakima River.

The reservoirs typically peak in mid-June as the snowpack melts. The reservoirs decline throughout the summer and fall as farmers irrigate.

Lynch called the March report an “early bird forecast” that calls for estimating how much water will be in the reservoirs on April 1. For now, the reservoirs look promising.

Heavy rain in late February broke what had been a dry month in the region. The rain increased the amount of water running into the reservoirs, which were at 124% of normal on March 1.

The rain, however, also reduced the snowpack. By March 1, the basin’s snowpacks held 94% of their average amount of water for the date.

Once the snowpack starts running off, it’s like a fast-moving freight train and not easily stopped, Lynch said. Besides more snow, cold weather to stop the melting will help, he said.

“We still depend on the snowpack even though we have good reservoir contents at this point,” Lynch said.

The snowpack typically peaks in April. The National Weather Service’s Climate Prediction Center forecasts that March, April and May will be cooler and wetter than average in the Pacific Northwest.

The forecast counts on a La Nina persisting in the Pacific Ocean throughout the spring.