A weak to moderate La Nina in the tropical Pacific has probably peaked, though it may have enough punch left to swell Northwest snowpacks, climatologists reported Thursday.
The National Oceanic and Atmospheric Administration said that the cooler-than-normal ocean likely will begin warming, but won’t reach average temperatures until the spring. Climatologists estimated the chances of La Nina sticking through the winter at 90 percent.
La Nina stacks the deck in favor of cool and wet weather in the Northwest for the next few weeks, Washington State Climatologist Nick Bond said.
“It’s not going to go away right away,” he said. “There’s no reason to think we won’t have a typical response to La Nina.”
Temperatures along the equator between South America and the international dateline were 0.8 degrees Celsius below normal, the same as in December, NOAA said in a monthly report. Temperatures lower than 0.5 degrees below normal qualify as La Nina conditions.
La Nina conditions generally mean below-average temperatures and above-average precipitation in the northern tier of the U.S. La Nina has the opposite effect on the southern tier.
La Nina has yet to deliver huge amounts of snow for summer irrigation in the Northwest. Snowpacks in 11 basins in Washington on Thursday ranged from a high of 109 percent of normal in northeast Washington to a low of 70 percent in the south Cascades, according to the Natural Resources Conservation Service.
“Our snowpack is OK, but it’s not above normal in most spots,” Bond said. “The next week or two should be on the wet side. I think it’s going to turn around.”
Precipitation will be above normal for the Northwest and Northern California for the next two weeks, according to a forecast issued Wednesday by the Climate Prediction Center. The odds are particularly high for wet weather in Oregon and Northern California. Also, temperatures are expected to be below average.
“We got off to a pretty good start” on snowpacks, Bond said. “While there was a hiatus in December, it looks like it’s going to resume, at least for a while.”
Federal climatologists will issue a new three-month seasonal outlook Jan. 18.
Oregon snowpacks in 12 basins are below normal for this time of year, according to NRCS. The snowpacks ranged from a high of 54 percent of normal in northeast Oregon to a low of 29 percent in the Klamath Basin in Southern Oregon on Thursday.
NRCS charts snowpacks in 21 basins in Idaho. Panhandle snowpacks are around 100 percent of normal. Snowpacks in the southern half of the state are generally smaller. The Owyhee Basin in the southwest corner of the state was 43 percent of normal on Thursday.
In California, snowpacks in six basins ranged from 86 to 68 percent of normal Thursday, according to NRCS.