This week, an early season storm hit the Sierra Nevada Mountains of California, burying them under feet of snow. The blizzard allowed one ski area, Mammoth Mountain, to open for business yesterday, ahead of schedule. And after a few tough winters, that’s great news for the resort, which gave the credit for its changing fortunes to a monstrous-sounding weather pattern: “Godzilla El Niño.”
That’s what the news outlets have taken to calling it, at least. Meteorologists say that the current El Niño will likely be one of the strongest in recorded history, rivaling the intense events of 1982-83 and 1997-98. And because of powerful connections between El Niño’s home turf — the tropical Pacific Ocean — and global circulation patterns, the impacts will be felt around the world, including in drought-stricken California.
There, many hope El Niño will replenish the state’s depleted reservoirs and nourish the Central Valley’s parched fields. So will it? We’ll get to that — and the Godzilla bit — in a minute. But first, here’s a quick refresher on El Niño, and how it influences California’s weather.
In neutral years (i.e. no El Niño or La Niña), easterly trade winds blow surface waters in the tropical Pacific to the west, where they form a pool of warm water near Indonesia. In the eastern tropical Pacific, near Peru, cold water from the deep ocean rises to take their place. This temperature pattern in the ocean helps drive a complementary pattern in atmospheric circulation. Moist air rises over the warm western tropical Pacific and sinks over the cool eastern tropical Pacific, where it fuels the trade winds that started the whole thing in the first place. You see, it’s a tightly coupled system.
During an El Niño, however, something happens to break the cycle. Often, the trigger is a burst of westerly winds that combat the trade winds, allowing the warm waters in the western tropical Pacific to flow eastward. Once this happens, a new atmospheric pattern (see below) can set up and lock the ocean changes in place, allowing a full-blown El Niño to develop. Once established, anomalously warm waters can linger in the eastern tropical Pacific for months. This happens, on average, every 2 to 7 years.
El Niño has significant impacts in Peru, where El Niño events coincide with warm, wet weather and poor fishing conditions. But the effects reach far beyond South America. That’s because, during an El Niño, air rises over the central or eastern Pacific, instead of in the west, like normal. This air displaces other regional circulation patterns around the world. In particular, it changes the position of jet stream, which dominates mid-latitude weather by directing storm tracks.
In general, these changes result in wet weather in California and across the American South, and mild temperatures in the northern parts of the country. However, every event is different, depending on the exact location of the warm water pool in the Pacific and the intensity of the warming. These factors also determine El Niño’s effect in far-flung locations. That’s why everyone is so fired up about this year’s event: temperatures have already climbed more than 3° Celsius above normal in the eastern tropical Pacific, meaning it’s shaping up to be a doozy. Or, if you prefer, Godzilla.
More importantly, however, many experts point out that one year of high rainfall probably won’t be able replace the most precious resource lost to the drought: groundwater. A recent report from the US Geological Survey shows that supplies have been in decline since the 1980s. That trend won’t turn around after a single El Niño, which won’t last more than a year and a half. To make matters worse, a strong El Niño event often leads to La Niña, the opposite phase of the cycle, in which water in the eastern tropical Pacific is anomalously cold. La Niña events are often associated with dry conditions in California and can sometimes last for two to three years.
In short, this year’s El Niño could deliver short-term relief from California’s suffering — and perhaps some good skiing — but the long term effects remains uncertain. We’ll just have to wait and see what Godzilla brings.
Learn more about how the ocean and atmosphere interact to produce weather in our module on the Hydrologic Cycle.
Learn more about what El Niño is and how it works over at NASA’s Earth Observatory.
Read the full forecast for 2015 from NOAA’s Climate Prediction Center.
Written by Julia Rosen
Julia Rosen is a freelance science writer and PhD student at Oregon State University. She received a Bachelors degree in Geological and Environmental Sciences from Stanford University before beginning her doctoral research on polar ice cores and climate change. In between, she did her Master's in backpacking around the world and skiing. Julia is a periodic contributor to Oregon States research magazine, Terra, and helps write blog content and develop learning modules for Visionlearning.