In El Nino years, the waters in the equatorial Pacific become warmer than average, which is opposite from the cooling waters that marked the La Nina conditions we've had the past two winters.
Right now, we are officially in neutral conditions, having killed off La Nina last month. Sea surface temperatures in the area where it counts in the Pacific are at -0.3C with respect to average conditions. Neutral is considered anything from -0.5C to +0.5C with El Nino being warmer than 0.5C and La Nina being cooler than -0.5C.
But latest forecast models, which had originally been leaning staying neutral (whose winters usually run the gamut of periods of rain/storms and periods of dry/boring) are now starting to trend toward El Nino conditions -- much like they did this time last year when the neutral forecast started shifting toward a second La Nina.
In fact, now models indicate a slight edge to El Nino conditions over neutral conditions (49% vs 44%), with a very slim chance (7%) of another La Nina winter. Just two months ago, models predicted a 53 percent chance of a neutral winter, a 32 percent chance of an El Nino and a 14 percent chance of a third La Nina.
Here are some of those models. Remember, anything over +0.5C anomaly is considered El Nino:
You can see the trend is for continued warming. The only question is: How warm?
El Nino years in the Pacific Northwest are typically marked by warmer temperatures and below normal rainfall with little -- if any -- lowland snowfall. It's these winters where mountain snowpack typically suffers as we're drier to begin with, but what precipitation does fall usually comes with a higher snow level.
The dry, warm weather comes from a split in the storm track to where the main jet stream goes well to our north, allowing warmer air to trek further north, while a strong southern branch of the jet stream will pummel southern California and the Desert Southwest. While El Nino usually means warm/dry winters here, it frequently means a very stormy winter in Los Angeles, especially once you get into January and February. The rest of the South also gets a wetter winter as those storms continue their general trek along I-40. Meanwhile the northern U.S. gets a break with a milder winter.
Back here, the last few El Nino periods were the winter of 2009-10 (very little lowland snow), the winter of 2006-07, a weak event in the winter of 2004-2005 and another event in 2002-2003. You might recall that last one was the winter that the passes had hardly any snow and we went through that big power crunch.
Now, El Nino, just like its sister La Nina, are just a weighing of the dice one way or the other, not a slam dunk. There have been instances where an El Nino winter ends up wetter and/or cooler than normal, just that in a majority of cases, we lean warm and dry. But while we should have some snow in the mountains, skiers can only hope that we end up with the neutral winter conditions instead of actually heading into El Nino.