Big storms around the holidays have left snowpack and reservoir levels in good shape throughout the West, as Oregon’s snow level was 166% of normal and California’s was above average as of Monday, Jan. 6.

La Nina atmospheric conditions, which favor colder northern systems, combined with a parade of atmospheric-river storms in November and December to leave a deep layer of snow throughout much of the region.

Snowpack levels are above their 30-year averages in Oregon (166%), Nevada (131%), Idaho (119% south of the Salmon River), Washington (115%) and California (110%), according to the Natural Resources Conservation Service’s National Water and Climate Center.

Precipitation is also above its seasonal average in many Western states, with Oregon leading the way at 130% of normal rain and snow, according to the center. California has registered 106% of normal precip as of Jan. 6.

Southwest still dry

The Colorado River Basin has recorded near-normal rainfall and snowfall this season, although Arizona and southeastern California are severely lagging. Arizona has only managed 16% of its median snow-water equivalent, according to the climate center, as severe and extreme drought is slowly expanding through central and western Arizona as well as southeastern California.

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“There’s been quite a gradient in the amounts of precipitation from north to south” so far this season, said Andy Reising, the California Department of Water Resources’ snow surveys and water supply forecasting unit manager. He noted that the northern Sierra Nevada had registered more than 150% of its normal snowpack as of the start of January, while the southern Sierra had only measured about 75%.

“Recent water years have shown us how quickly water conditions can change,” Reising told reporters Jan. 2 at Phillips Station near Lake Tahoe, where he was conducting the season’s first manual snow survey. “Currently the forecast window is dry. Most of the storms that are predicted are going to be north of California over the next two weeks.”

The federal Climate Prediction Center foresees above-average chances of precipitation in the Pacific Northwest and northern Rocky Mountains over the remainder of the winter, but most of California could be wetter or drier than normal. The forecast comes as the currently weak La Nina conditions are expected to fade by spring.

In California, December storms prompted the DWR to increase its planned 2025 water deliveries from 5% to 15% of requested supplies. The allocation could keep changing as the winter progresses, depending on precipitation and anticipated spring runoff, officials said.

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Major reservoirs statewide entered the New Year at 121% of average thanks to two consecutive years of above-average snowpack conditions, the DWR noted. Shasta Lake, the centerpiece of the federal Central Valley Project, was at 130% of average and 78% of capacity as of Jan. 6, according to the California Data Exchange Center. Lake Oroville, the State Water Project’s chief reservoir, was at 128% of its normal water level and 70% of capacity.

The U.S. Bureau of Reclamation typically unveils its initial CVP allocation in late February.

Regional totals

Here are the current snowpack and seasonal precipitation totals for Western states and regions, according to the National Water and Climate Center’s Jan. 6 update:

Arizona: Snowpack 16% of median snowpack, 30% of median precipitation.

California: Snowpack 110%, precipitation 106%.

Colorado: Snowpack 98%, precipitation 100%.

Idaho (north of Salmon River): Snowpack 115%, precipitation 97%.

Idaho (south of Salmon River): Snowpack 119%, precipitation 101%.

Montana: Snowpack 95%, precipitation 86%.

Nevada: Snowpack 131%, precipitation 113%.

New Mexico: Snowpack 36%, precipitation 78%.

Oregon: Snowpack 166%, precipitation 130%.

Utah: Snowpack 98%, precipitation 95%.

Washington: Snowpack 115%, precipitation 100%.

Wyoming: Snowpack 90%, precipitation 85%.

Colorado River Basin: Snowpack 100%, precipitation 99%.

Columbia River Basin: Snowpack 124%, precipitation 99%.