If anyone is eagerly following news of the strengthening El Niño in the Pacific, it’s California. Strong El Niño events have a history of bringing drenching rain to the West Coast during the winter months, and we could see that play out this year. However, don’t get too wrapped-up in the hype—it’s going to take more than one rainy stretch to ease the damage done by the lasting drought.

What It Is

In order to understand what El Niño may or may not do for California, we need to understand El Niño itself, and shockingly (!!!) the national media doesn’t do a great job explaining things that could get them a lot of ratings if they spin it just right (see: polar vortex).

If you’re not familiar with El Niño, it’s an occasional warming event that occurs in the eastern Pacific Ocean that can have wide-ranging effects on global weather patterns.

An El Niño occurs when trade winds in the equatorial Pacific Ocean relax or even reverse direction, allowing warm water to pool up in the eastern half of the basin. The eastern Pacific around South America usually experiences cold currents and upwelling—that is, cold water from deep in the ocean rising to the surface, leading to cooler water temperatures than those found in surrounding areas—so when this water suddenly warms by several degrees, things start to go haywire.

It takes a prolonged period of sea surface temperature anomalies of at least +0.5°C for the warming to be considered an El Niño, especially in that Niño 3.4 zone, which covers a nice chunk of the ocean around the Equator (illustrated in the tiny map above). As you’ve probably heard breathlessly reported over the past couple of months, we’re currently experiencing an El Niño, with water temperatures coming in an average of 1.75°C warmer than normal as of the latest analysis by the Climate Prediction Center (PDF file). The greater the positive temperature anomaly—meaning warmer waters and a stronger El Niño—the greater the odds that the phenomenon will start to mess with weather patterns.

In the United States, aside from dry conditions in the northwest and fewer hurricanes than normal in the Atlantic basin, the most prominent effect an El Niño can have is producing a wet winter in the southern half of the country, including central and southern California. The warmer Pacific can cause the the sub-tropical jet stream to form farther north, allowing disturbances and storm systems to form over the Pacific and plow into California, bringing strong winds and heavy rain.

What It Isn’t

El Niño isn’t new, and it’s not something we recently discovered. The name of the phenomenon translates to “the little boy” in English, as Spanish-speaking fishermen came up with the name for the oceanic warming event as they usually noticed it around Christmas, naming it in honor of li’l baby Jesus.

The warming pattern also isn’t a magic solution to all of the West Coast’s woes. The atmospheric effects of an El Niño aren’t guaranteed. Discussion of this phenomenon’s effects needs a disclaimer like you’d see on a weight loss commercial: no case is typical, results may vary.

History tends to repeat, and we tend see wet weather in the southern tier of the United States during a stronger El Niño, but saying “California is definitely in for beaucoup rain!” is kind of like promising a big blizzard in February when it’s still July. If the warming pattern continues—and all indications seem to say it will—overall conditions will be favorable for disturbances and storms to develop and affect the West Coast, but we’ll have to take it on a week-by-week basis to see what’s actually going to happen.

California’s Drought

The latest update of the drought monitor doesn’t paint a pretty picture across the western United States. Believe it or not, the drought has improved by a hair since September 30—California started the water year with 58% of the state in an exceptional drought, which is the worst of the five categories. As of last Tuesday, only (“only”) 46% of the state is in an exceptional drought. Any progress is progress, I guess.

The intensity and duration of this drought is unprecedented in the modern era, and it’s going to take more than a month or two of rain to fix what’s gone so horribly wrong over the past couple of years. The problem with the potential of seeing big bursts of heavy rain is that much of the rain will run off, helping reservoirs and bodies of water no doubt, but causing floods, mud and landslides in the process, not to mention the water being unable to seep into and rejuvenate the soil. This doesn’t even begin to cover the fact that (currently non-existent) snowpack is a huge water resource in the state.

How much rain will it take to get California (and everyone else in drought) back on track?

The above map from the National Centers for Environmental Information (formerly the NCDC) shows the amount of precipitation (rain and water-equivalent) it would take to end the drought and begin replenishing the environment over the next six months. Much of California needs to see between nine and twelve inches of rain between now and January 6, 2016, in order to both pull itself out of the drought and start making the situation better.

That’s nothing for those of us out east—hey, parts of Florida saw that much rain just this weekend—but getting a foot or more of rain in six months is a heavy lift for many spots out west, especially seeing that average rainfall totals and drought indicators act kind of like compounding interest. The longer you go without rain, the more rain you need to bounce back, and the harder is it for that much rain to fall in the necessary amount of time, making the drought worse and further feeding the ugly feedback cycle.

As we listen to more reports of a strengthening El Niño, Californians are getting restless and excited at the prospect of drenching rain thanks to part of the Pacific Ocean getting balmy. If history and trends hold true, you could be in for a wet winter, but keep in mind that it’s probably not going to be enough to make everything better. It takes long-term relief to fix a long-term disaster.

[Images: AP, earth.nullschool.net, CPC, author, NCEI]

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