NOAA issued their annual winter outlook for the United States Thursday and it certainly has a La Nina flavor to it, meaning the Pacific Northwest is likely in for another wet and cool winter.
That conclusion was widely expected after NOAA declared that La Nina conditions had returned for a second go-around in September.
A quick recap: La Nina is part of a 3-7 year cycle where ocean temperatures in the Equatorial Pacific Ocean region drift from warm to cold, then back again. The warm phases are called El Nino, the cold phases are La Nina, and "neutral" is what we get when they're in the middle, or average. The shift in water temperatures has a cascading effect on global weather patterns that begin with a change in the trade winds near the equator.
For us, the main domino effect is to arc the typical position of the jet stream to the north into the cooler waters of the northern Pacific Ocean, then aim our way, pushing all that cold rain into the Northwest.
And thus, La Nina winters typically spell cool, wet (and snowy) winters around here.
La Nina should be a familiar friend (foe?) as we went through this last winter as well, although last year we really didn't get the full force of La Nina until the heart of winter had passed. (In essence, last year's winter was probably a little tamer than it should have been.) We paid for it in spring (and early summer) but in exchange really didn't have too many snow events.
We'll see how this winter goes now that La Nina has a running start. If nothing else, it should be another good ski season and the mountains should receive a healthy snowpack for next year.
Here are the official forecast maps issued Thursday for the December through February period. Note the Pacific Northwest has been given higher than average chances for cooler than normal temperatures (the blue swath) and much higher than average chances for a wetter than normal winter (green swaths). (These are just fancy versions of their usual 90 day forecast maps.)
These maps were for December through January but if you look at their other maps for their forecasts further out, they keep the Northwest generally cooler and wetter through spring again.
But while skiers are licking their chops, La Nina does spell bad news for the south, as while it's usually quite wet up here, it's very dry down there. That gives dim hope that the severe drought conditions will relax anytime soon.
By the way, if you're wondering, these "Double Dip" La Ninas where go two back-to-back are not unusual -- NOAA says there is a standing 50 percent chance of a secondary La Nina to follow a strong event as we had last winter. Usually the second dip is weaker than the first. (NOAA did say this event will count separate from last winter's La Nina, which officially ended in May.)
What's with NOAA's "Wild Card"?
If you did read the NOAA forecast, you'll see they allude to some "wild card" that could trump La Nina.
They're talking about the Arctic Oscillation" which is yet another climate factor that can influence weather patterns. This got some national attention last winter as one reason the East Coast was getting slammed with persistent snow storms as the AO seemed to be stuck in the negative phase. Typically this pattern can shift every couple of weeks and in turn, shift the weather conditions around.
Then there is also the "North Atlantic Oscillation" and the Pacific Decadal Oscillation that all have influences as well, which is just a fancy, hyperlinked way of saying that long range climate forecasting is complex and why no two winters are alike, La Nina or not, and don't expect the same weather every day!