Weather Blog

La Nina: Not a slam dunk, but preferable to the alternative?

La Nina: Not a slam dunk, but preferable to the alternative?

You'd have thought NOAA announced that the Space Needle has a 50 percent chance of being traded to Portland for the Burnside Bridge or something. Rumors are running rampant that La Nina is forecast to return this winter!!!

But before you close your laptop or set down your smartphone so you can properly wave your arms in panic as you run through Pioneer Square, let's first delve into what NOAA is actually saying, because what I'm reading in a lot of places is misinterpreting the forecast.

What NOAA has said is there is a 50 percent chance that we could have a La Nina winter -- and what's being ignored -- a 50 percent chance we will maintain a neutral winter.

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.

La Nina winters typically spell cool, wet winters around here while El Nino winters are typically warm and dry. Neutral winters? We'll get to that in a second.

We just came off a pretty strong La Nina last winter that carried into spring before officially fizzling to "neutral" status in early June. However, the atmosphere never noticed, and La Nina-type conditions persisted through... well, now. Typically La Ninas don't mess with the spring and summers but as you've seen, this year's versions have been officially messed with. August is on track to be the seventh-consecutive month with below-normal temperatures.

The usual trend is to come off of La Nina and go into a neutral winter, which is where all signs have been pointing this summer.

Until now.

Lately, the ocean is starting to show some cooling again. And some forecast models are indicating that we're heading back to La Nina -- a "Double Dip" La Nina has some have dubbed. But other models maintain neutral is the way to go.

With the chance of La Nina, NOAA has issued a "La Nina Watch" but that is just that conditions have potential to go that way -- not an official declaration that it's coming or here! It's not until we get to a "La Nina Advisory" -- which is where we were this time last year -- that La Nina is really in the cards.

These "Double Dip" La Ninas are not unusual, especially in the wake of a strong event as we are now. Usually the second dip is weaker than the first. That said, last fall and winter didn't really follow a typical La Nina script -- La Nina didn't really rev up until February and March. Perhaps this winter could be different since we have a head start now.

Careful what you wish for:

But let's talk about the alternative: The neutral winter. While La Ninas tend to have a bias toward cool and rainy -- and a little snowier -- than a usual fall and winter, neutral winters tend to be the stormiest.

Most of the region's greatest storms -- be it snow storms, wind storms, or flooding rain storms -- have come in neutral years. These winters are usually trademarked by a variety of conditions -- anything from cold snaps,warm snaps, rainy streaks, wind storms, and extended dry, foggy "burn ban" periods, to all of the above.

Jason Phelps, a local climate researcher, has detailed some of the events that have occurred in the past 30 years of truly neutral winters. They include the big snow storm of December 1996, the Inauguration Day storm of 1993, the big floods and major Christmas snow of 1990. (We haven't had a really good solid neutral year in a while -- usually leaning one way or the other. The big December snow of 2008 was technically a neutral year but just barely under the minimum threshold for a La Nina winter. Same goes for winter of 2005-06.)

Suffice to say, while neutral years typically don't end up as snowy as La Nina years do when all is said and done, it's not like we usually skate through scot-free.

NOAA should have a better handle on whether we are going back to La Nina by the start of fall. In the meantime, it's not a given. Then, again, the alternative isn't much calmer.

(You can put your smartphone and/or laptop down now.)