YAKIMA, Wash. — The forecast calls for a full water supply for irrigators in the Yakima Basin, but experts say that prediction could change as warm weather melts the snowpack in the Cascade Mountains about a month earlier than desired.
A lack of significant snowfall in February is another contributing factor, they said. The chances of significant new snowstorms are also slim.
If that scenario continues to play out, some irrigators in the Yakima Basin could have less than normal water supply in August.
Statewide snowpack was 100 percent of normal on March 1, down from 109 percent on Feb. 1 and 120 percent on Jan. 1, said Scott Pattee, water supply specialist of the Washington Snow Survey Office of the USDA Natural Resources Conservation Service in Mount Vernon.
While the snowpack is good, its water content is 10 percent greater than normal for this time of year, Pattee said. That’s from more rain than snow and will hasten runoff, he said. Temperatures have been 5 to 15 degrees above normal for the last month or two, he said.
“If we continue these warm temperatures, (mid and higher-level) snowpack will ripen and start melting sooner and faster than normal and than we want it to,” he said.
Snowpack below 3,000 feet already has melted and everything below 4,000 likely will be gone by April 1, he said. Peak snowpack is usually about April 1 but this year it is probably about now, he said.
There were a couple 4- to 5-inch snowfalls in the Cascades in February, but that’s not much and chances of any more large snowfalls are not good, he said.
Irrigators in the farm-rich Yakima and Kittitas valleys usually depend on snowpack runoff for April and May and avoid tapping mountain water reservoirs until June.
That likely will accelerate one month and some irrigators could be short of normal water in August, Pattee said.
During last year’s drought, Yakima Basin irrigators had to begin using reservoir water on April 1 and water supply for junior water right irrigators was cut to 47 percent of normal. Along with excessive heat, it cost basin growers millions of dollars in crop losses.
The five reservoirs serving the Yakima Basin — Keechelus, Kachess, Cle Elum, Bumping and Rimrock — totaled 76 percent of capacity on March 7, up from 57 percent on Feb. 1, according to the U.S. Bureau of Reclamation in Yakima. All together they now are storing 809,759 acre-feet of water and total capacity is 1,065,400 acre-feet.
“We are in a good position to fill the reservoirs but we don’t know when we will have to start using them,” said Chris Lynch, USBR hydrologist.
“We like to make it into June before we start drawing on them but sometimes we have to start drawing Keechelus in May,” he said.
Precipitation was 110 percent of average in the Yakima Basin in February and is 133 percent so far for the water year, he said.
Streamflows for April through September will be slightly under 100 percent of normal and will closely follow snowpack readings, Pattee said.
As of March 1, the Spokane Basin snowpack was 88 percent of normal. The upper Columbia (Okanogan and Methow rivers) was 122 percent. The central Columbia (Chelan, Entiat and Wenatchee) was 118 percent, the upper Yakima was 95 and the lower Yakima was 102. The lower Snake was 98 percent and the lower Columbia was 94.
South Puget Sound (from Cascade crest to lowlands) snowpack was 95 percent, central Puget Sound was 88, north Puget Sound 100 and the Olympics was 103.
The lowest reading was the Skykomish Basin at 62 percent and the highest was the Methow at 135.