Before I get into this article, let me start out by saying that El Nino/La Nina are two very important events that can have major impacts around the globe. Entire economies can be positively or negatively affected by the emergence of an El Nino or La Nina event, which is why it’s important to predict that one is going to occur many months in advance. About this time last year, there was so much talk about how we were going into a Super El Nino, and that it was going to be just as bad as the 1997/98 El Nino event. I never really saw that happening, but I definitely understand why many did. The atmosphere just never responded early enough to what was going on across the equatorial Pacific, and if it had, I would have been wrong.
El Nino DID Affect This Winter:
NOAA announced the other day that El Nino had officially arrived. After that announcement, the media went crazy with the news, which had many people asking how El Nino is going to affect them. I’m glad you asked because I want to try to answer your questions. To answer the first question, many of you have already felt the influences of El Nino this winter.
When I put together my winter forecast (both in July and November), I took into account that a weak to weakly moderate El Nino Modoki would be in place during the winter months. In my early July winter forecast, I went against all of the super El Nino predictions, which would have changed the entire winter forecast had those predictions verified. Instead, we had the weaker El Nino that I expected.
A very active sub-tropical jet did set up across the southern U.S. particularly in February, which was likely partly driven by this weaker El Nino. Because of this El Nino being on the weaker side, the southern half of California didn’t benefit as much as I originally thought, but the effects were felt in many other locations. It’s important to realize that El Nino was not the main driver of this winter but was one component of many parts.
NOAA typically puts out pretty good short-term forecasts, but their seasonal forecasts are mediocre at best. They simply weigh too heavily on El Nino and La Nina and ignore everything else. They did the exact same thing this winter and had most of the northern U.S. with above average temperatures and the southern U.S. with below average temperatures. That is a carbon-copy of what a traditional moderate to strong El Nino looks like, but you just can’t do that and expect to have an accurate winter forecast. You just ignore too many other factors. Even with a moderate El Nino, you have to consider other factors.
This El Nino did not just come about one day like a light switch being flipped. I’ve noticed that many are saying that if this El Nino had come a few months earlier, then the winter outcome could have been different, especially for places like California. I disagree. Had it been stronger, then the outcome would have been different, but I never expected a stronger El Nino anyway. Those waters across the central Pacific have been warm since last year, and NOAA needed enough evidence that the atmosphere was responding to these warmer sea surface temperatures to make it official. They are the ones that flipped the switch in March.
I don’t blame the meteorologists at NOAA for the misinformation because they have years of experience and know what they’re doing. I blame the media. They needed something to talk about, and unfortunately, the writers of most of the articles and reports that were put out on this subject were off. That’s just my opinion, for what it’s worth.
What Is El Nino (Read this carefully b/c it may take a few minutes to fully understand)?
I wrote an article last year, where I went into detail explaining what El Nino is. In the future, I plan to either rewrite that article or add updated information to the old one.
Winds called trade winds blow from east to west across the equatorial Pacific. During an average year, the sea surface temperatures are cooler across the central and eastern equatorial Pacific and warmer over the western parts. The warmer/cooler sea surface temperatures warm/cool the air above it. Warm and moist air is less dense, so it has the tendency to rise. As you can imagine, when the air molecules are being pulled upward, areas of low pressure develop at the surface. Air from other regions try to replace the air that’s been pulled up, so that’s how you get wind.
Because the waters are typically cooler over the central and eastern equatorial Pacific and warmer along the western equatorial Pacific, high pressure and less stormy conditions develop particularly over the eastern equatorial Pacific and low pressure over the western equatorial Pacific. Winds blow from high to low pressure for the reason I explained above, so that’s why your winds are typically east to west over this region.
These winds then pile up the warmer water over the western equatorial Pacific and upwell cooler waters from the eastern Pacific, which in turn, creates an even stronger temperature/pressure gradient. This makes the winds even stronger. As you can tell, it takes both the atmosphere and the ocean to make this entire process work. It’s a feedback loop.
Typical year vs. El Nino year (Graphic from Norman Snell):
When El Nino begins to develop, something changes! Without getting into much detail, something has to occur that begins to break down this entire process. Around this time last year, a wave developed that started to move the warm western Pacific waters eastward. Now, this is oversimplifying things a bit, but you get the idea. Once these warmer waters started moving east, it started to warm those cooler waters farther east. This then started to weaken the trade winds because guess what? The temperature/pressure gradient was weaker. The only problem last year was that the atmosphere just didn’t respond to these warmer waters being transported east. The trade winds never weakened enough for long enough to keep this feedback loop going. Outside influences may have been the cause, but this kept the El Nino on the weaker side.
During stronger El Nino years, the trade winds will actually reverse course and flow from west to east. Why is that? Well hopefully you know the answer to that. Warmer waters have now been pulled farther east and cooler waters are now farther west. Now the higher pressure is west and the lower pressure east. Remember, wind goes from areas of high to low pressure because it’s trying to replace that air.
The current El Nino is a weak El Nino Modoki. That is when above average sea surface temperatures in the equatorial central Pacific are sandwiched between cooler waters to the west and east. I’ve talked about all of that on this site before.
If you didn’t understand all of that, it’s fine. This is just for your information and for those of you that want to learn something new. This is a very simplified explanation of a very complex process.