El Niño and La Niña: Weather's Sibling Rivalry - dummies

El Niño and La Niña: Weather’s Sibling Rivalry

Just when you think you’ve got the seasons in your area all figured out, along comes a winter that is nothing like what you expect. Around the country, around the world, everything seems to be upside down. Places like Seattle that are accustomed to cool temperatures and a lot of rain instead get warm, dry weather. Places like sunny southern California, the Southwest desert, and even the southeastern United States get cold temperatures and heavy rain. In the usually cold Northeast, it doesn’t even feel like winter. And it snows in weird places like in Guadalajara, Mexico.

That’s almost a sure sign of El Niño — above-average Pacific Ocean sea surface temperatures and atmospheric conditions that change the places where storms go.

Cold temperatures and rain befall the usually dry deserts, and warm dryness comes to the usually cool forests of North America, South America, and much of the rest of the world. The important thing is not that there is more hard winter weather around the world during El Niño — although during a big El Niño, a grande El Niño, there certainly seem to be more storms. El Niño’s “Bad Boy” reputation as a natural disaster comes not from extra storminess, but from the fact that it puts storms in places that can’t handle them so well.

Is El Niño a bad boy?

Is El Niño really bad news? It all depends on where you live. A powerful El Niño is terrible news to people in Ecuador and Peru, for example, who often face deadly floods in their steep desert terrain. It’s not much good to southern California either, and for the same reason — the desert soil can’t absorb much water, so the rains bring on floods and mud slides. But the folks in Seattle and western Canada don’t mind a mild winter once in a while. In the northeastern United States, often El Niño means milder winter temperatures and less snow than usual — less hardship and a welcome savings on winter heating bills. And for people across the Gulf States and the Eastern Seaboard, El Niño does one really good thing in the Atlantic Ocean in the summer and fall. It generates powerful high-altitude winds that cut the tops off of tropical storms before they can grow into hurricanes.

Good or bad, scientists say that, aside from the seasons themselves, El Niño is the most powerful climate force on Earth. So this is a big part of the big answer to the little question: Why is one winter different from another? It’s not the only reason, of course. But if one winter is very different from normal — almost the opposite of what you would expect — take a look out in the tropical Pacific Ocean.

The El Niño look

If El Niño is out there, as it is in Figure 1, the Pacific Ocean has a very different look. The Warm Pool and the big thunderstorms have moved. Instead of up against south Asia, they are spread out into the middle of the Pacific or even far over on the other side of the ocean, up against the coast of South America. All kinds of big changes are taking place. The tradewinds have completely pooped out and may even be blowing in the opposite direction. The Cold Tongue is a goner, and in its place is extra-warm water. Take a look at the jet stream, the storm track. Instead of looping around like it normally does, it is so strong that it carries storms straight over the Pacific Ocean and across the Southwest and the southern United States.