La Niña Swells Water Supply in Washington

By Don Jenkins, Capital Press

An ongoing La Nina enhances chances that late winter and early spring in Washington will be cool and wet, the federal Climate Prediction Center forecasted Thursday.

The outlook for March, April and May bodes well for building and preserving snowpacks that already are deeper than normal. La Nina’s affect was relatively slight until recently, Washington State Climatologist Nick Bond said.

“It took its sweet time,” he said. “We hadn’t seen the atmospheric weather patterns that tend to come together with La Nina, but that changed this month.”

A cooler than average Pacific Ocean along the equator triggers a La Nina, the opposite of an El Nino. In La Nina years, winters in the northern tier of the U.S. are generally colder and wetter.

In the southern tier, La Nina winters tend to be warmer and drier. Oregon and Idaho south of the Panhandle fall in between those bands.

Basin snowpacks in Washington were mostly well above average on Thursday, led by the Olympic Mountains at 135% of normal. The Upper Columbia basin was 126% of normal, and the Lower Snake basin was 114% of average.

Statewide, basin snowpacks averaged 118% of normal. There is one note of caution. Although the next three months are expected to be wetter than normal, March is expected to be about average, according to the prediction center.

A warm wind could still dry out snowpacks, Natural Resources Conservation Service water supply specialist Scott Pattee said.

Snowpacks, however, look strong right now and are nearing the point they only need “maintenance snow,” he said.

“We’re looking pretty good. If we hold onto what we have, we should have a good water supply,” he said.

The five reservoirs that irrigate Yakima Valley farmland held 109% of their average volume on Thursday. Rainfall has been above average at the reservoirs, and the snowpacks that melt into them are above average, too.

“The conditions right now are looking very favorable for an adequate water supply,” said Chris Lynch, Bureau of Reclamation river operations engineer.

The Climate Prediction Center, part of the National Weather Service, forecasts that sea-surface temperatures will warm to an average range — or neutral state — by late spring.

For now, La Nina should continue to influence the weather, Bond said.

“I would think it will for at least another month, month and a half,” he said.

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