The odds favor a wet and cool winter in Washington and most of Idaho and Oregon, the National Oceanic and Atmospheric Administration said Oct. 21, releasing a winter outlook that bodes well for Northwest snowpacks and next year’s irrigation season.

NOAA’s Climate Prediction Center based the forecast on a La Nina that formed in October and is expected to persist until spring. The climate phenomenon does not have uniform effects across the U.S.

While conditions are expected to improve in the Northwest, the drought likely will worsen in the Southwest, NOAA said. In some parts of the country, La Nina’s influence is too unpredictable to tilt the odds either way.

Cooler than normal sea-surface temperatures along the equator in the Pacific Ocean triggered the La Nina. A reservoir of cold water below the surface suggests that the ocean will continue to cool and that the La Nina will stick around and may get stronger, according to NOAA.

Sea-surface temperatures off the West Coast are also cooling, an expected response to a La Nina, NOAA reported.

The winter forecast projects the expected climate in December, January and February. It does not predict snow accumulations.

Above-average temperatures and below-normal precipitation are favored for the southern U.S. The South has the best bet for a warm winter, according to NOAA.

A La Nina also prevailed last winter. A large snowpack in the Cascades fed irrigation systems in Washington, even though drought caused by a dry spring gripped the state.

NOAA on Thursday also released an outlook for November.

Oregon, Northern California and southern Idaho are expected to be warmer than usual. Washington, Oregon and Idaho are expected to have above-normal precipitation.