It’s back. Maybe.
The climate phenomenon known as La Nina appears to be shaping up again in the Pacific Ocean, which could mean another cool, wetter-than-normal winter in the Pacific Northwest, according to the National Oceanic and Atmospheric Administration.
NOAA’s Climate Prediction Center on Thursday upgraded last month’s La Nina watch to a La Nina advisory. Forecasters have recently observed the cooler-than-usual Pacific Ocean temperatures that characterize La Nina, and the condition is expected to strengthen in the coming weeks and months, according to NOAA.
The natural phenomenon would be the second straight La Nina year in the Pacific, after a “fairly strong” pattern in 2010-11, said Dan Collins, a meteorologist with the Climate Prediction Center. What that means this time around remains to be seen.
“It’s not always the case that a strong La Nina leads to strong impacts,” Collins said. “It just happened to be the case that last year we had strong impacts.”
The 2010-11 version churned out much more rain than usual and huge mountain snow packs in the Northwest, but little in the way of biting cold. The weather pattern also tends to produce dry conditions for the southern United States, and a repeat of that would be bad news for drought-stricken states like Texas.
La Nina typically emerges every three to five years, but back-to-back occurrences are not unheard of, according to NOAA. In that case, the second one typically isn’t as strong as the first, Collins said. But with flooding and drought conditions already in place in various parts of the country, even a weak continuation of weather patterns can exacerbate those problems, he said.
The 2011-12 winter would be the third La Nina event in the past five years. Stuck in the middle of that run was an El Nino in 2009-10 — that’s La Nina’s counterpart, which gives the Northwest drier-than-usual conditions.
In other words, normal has been hard to come by recently.
“It’s erratic,” Collins said. “You don’t necessarily expect El Ninos to follow La Ninas and La Ninas to follow El Ninos.”
For the Washington State Department of Transportation, winter means preparing for any number of weather events. Last year brought a “mixed bag” of low-elevation snow and heavy rains at times, but nothing crews hadn’t seen before, said WSDOT spokeswoman Abbi Russell.
Southwest Washington can throw a wide variety of conditions at roads and highways throughout the year, she said. “Our crews are flexible, and we want them that way.”
The cool, wet pattern of La Nina can make an impact even if it doesn’t translate to snow, Russell said. That’s expected in the region’s mountain passes. But heavy rain elsewhere can cause problems through slides and flooding, she said.
The Northwest could see its precipitation “signal” for the winter develop within the next month or two, Collins said. NOAA will officially release its winter weather outlook in October.