Pacific Ocean temperatures are rising along the equator, a signal that winter likely will be warmer than normal in the Northwest.
Federal climatologists peg the odds that an El Nino will form in the next couple of months at 70 to 75 percent, a 5 percent increase since mid-September. The warm ocean should influence late winter weather, but El Ninos historically have had little effect on snow accumulation in Washington before Jan. 1, State Climatologist Nick Bond said Monday.
“Here’s hoping that holds true to form, and we get reasonably wet and cold weather in the mountains pretty soon,” he said.
The Climate Prediction Center revised its El Nino outlook on Oct. 11. The federal agency reported that surface temperatures rose across the Pacific during the previous four weeks and that warmer water spread over a larger area.
Winters are generally warm and dry in the northern tier of the U.S. during an El Nino. The last two El Ninos formed in back-to-back winters, 2014-15 and 2015-16.
In some years, such as 1995 and 2007, El Nino prevailed, but snowpacks in Washington were already above average by Jan. 1, according to an analysis by Bond. In other El Nino years, snowpacks were below average at the end of the year.
“I was surprised by how little effect there was,” Bond said. “It’s almost completely negligible before the first of the year.”
The 2014-15 El Nino was particularly notable. A “snowpack drought” was followed by a hot and dry spring and summer, combining to cause one of the most severe droughts ever in Washington. This year, however, ocean-surface temperatures just off the coast are not as warm.
“That’s one thing we have going for us,” Bond said. “We don’t have a really warm ocean off our coast.”
La Nina conditions have prevailed during the past two winters, which tilted the odds in favor of a wet and cool winter. Ocean temperatures warmed to neutral conditions last spring, and climatologists began to tentatively predict an El Nino.
In recent weeks, bursts of westerly winds have warmed sea temperatures and increased the odds of an El Nino.
“It’s poised,” Bond said. “If we get another burst or two, it will be a lead-pipe cinch.”