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 Niño 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 Niños historically have had little effect on snow accumulation in Washington before Jan. 1, State Climatologist Nick Bond said Oct. 15.
“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 Niño 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 Niño. The last two El Niños formed in back-to-back winters, 2014-15 and 2015-16.
In some years, such as 1995 and 2007, El Niño prevailed, but snowpacks in Washington were already above average by Jan. 1, according to an analysis by Bond. In other El Niño 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 Niño 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.”
Conditions are warmer, however, north of Washington state. “A pool of warm water is found over the north Pacific and Gulf of Alaska, with some of it over 2C warmer than normal,” University of Washington meteorologist Cliff Mass said in his blob on Oct. 16. “This is the signature of the ‘son of blob,’” referring to “the Blob” of abnormally warm seawater off Washington in 2013 to 2015.
La Niña 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 Niño.
In recent weeks, bursts of westerly winds have warmed sea temperatures and increased the odds of an El Niño.
“It’s poised,” Bond said. “If we get another burst or two, it will be a lead-pipe cinch.”