Not Every El Niño is the Same

The big question remains. When will these El Niño Storms finally hit Southern California? Skeptics will tell you that we in the media are over blowing the coverage. Making a big deal out of something that may or may not actually happen this Winter. Considering that forecasting Weather more than a week out is dangerous business, you might agree with those who simply don't believe El Niño is coming.

So what are we to make of all of this? I tell anyone that it's always better to be safe than sorry. Look, we live in Earthquake country. When the ground shakes we get no warning at all. We're told to prepare for the next big one by getting emergency kits ready just in case we find ourselves without water, food, electricity and other essential day to day items.

The big difference? As a trained Meteorologist, I'm able to tell you when the storm is coming, how long it will last and how much time you might have to make repairs, grab sandbags, etc. before the next big storm hits. Thanks to technology, it's really a luxury we didn't have even 100 years ago. So not matter what happens during the rainy months ahead, I say better to prepare now, call a roofer to fix that leak or get a supply of sandbags ready to go in advance of the next storm.

Despite what we have been saying about the current El Niño, it's important to remember that not every El Niño is not the same. We often talk about sea surface temperatures in the central equatorial Pacific near-record highs. But there are many other factors to consider.

Here is a little education put out today by part of NOAA.

Remember: ENSO is not all about the ocean

El Niño is phase of the El Niño-Southern Oscillation (ENSO). An ENSO event involves changes in both the sea surface temperatures and in the overlying atmosphere across the tropical Pacific. In the case of El Niño, sea surface temperatures are warmer than average, and the Walker Circulation, which operates like a vertical loop through the tropical Pacific atmosphere--is weakened. This weakness shows up as more clouds and rain in the central and/or eastern Pacific and less over Indonesia, weaker near-surface winds (the trade winds, that usually blow from the east to the west), and weaker upper-level winds.

The whole system is important, because there are feedbacks between the ocean and the atmosphere that help to strengthen El Niño. For example, weaker near-surface winds let the surface waters warm in the central and eastern Pacific. The warmer waters lead to more convection (rising warm air), which changes the circulation and further weakens the near-surface winds… and so on! (Check out Tom's post on the Walker Circulation for more details about the system.)

Another thing to remember about ENSO is that meaningful changes take place on seasonal timescales (the average over several months). The important effects of El Niño on the U.S. and other regions are related to its average strength over the fall and winter, not how strong it is on any particular day or week. We do monitor the weekly and monthly changes in the sea surface temperature and the atmosphere to get a hint at where things are headed, but we'll ultimately judge the strength of this El Niño by its average over the seasons.

Yeah, yeah - what about this one??

Right out of the gate, let's talk about that November sea surface temperature in the Niño3.4 region. The ERSSTv4 data set shows that this November was 2.35°C warmer than the November average--tied with November 1997's 2.33°C. (Yes, I know those numbers aren't identical, but they're within the statistical margin of error, which means as far as rankings are concerned, they're tied.), This dataset has been carefully maintained to ensure that it is historically consistent, so it's the best, most reliable one to use to compare 2015 to 1997 (or any other year.)

What does it all mean?

Every El Niño event is different, and even if there are some strong similarities between this El Niño and another, we'd be really surprised if everything lined up exactly the same. By most measures, this is one of the top three strongest El Niños since 1950, and there's still a chance it could record the highest Oceanic Niño Index (the three-month-mean sea surface temperature anomaly in the Niño3.4 region, our primary ENSO metric). But ocean temperatures are just one way to measure ENSO, which can be tracked in many ways.

While the warmer-than-average ocean waters are likely reaching their peak about now, they will remain a huge source of warmth for the next several months to drive the main impacts on temperature and rain/snow over North America, which typically follow the peak. The main impacts season is December-March, so we're just at the very beginning of finding out what this El Niño event will bring to the U.S. There's no doubt that El Niño 2015-2016, which has already shown its power around the world, will have a significant effect on the U.S. winter.

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