How does El Niño work, and why might it bring rain and snow to California this winter?  In this post we take a deep dive to answer these questions.

How might El Niño affect California?

There’s a favorable chance that this winter will be wetter than average in much of California — from San Diego to San Francisco. The greatest chance for wet conditions is in Southern California, says the National Oceanic and Atmospheric Administration’s Climate Prediction Center.

But there’s only an equal chance of a wetter-than-average rainy season north of San Francisco, where much of the state’s water supply is collected and stored in giant reservoirs. California needs both rain and snow up there. Snow slowly melting from the mountains is essential to recharging our reservoirs when the skies turn dry later in the spring.

We’ve had experience with El Niño before, a weather phenomenon characterized by the warming of Pacific Ocean waters west of Peru that causes changes in the atmosphere and can dramatically alter weather worldwide.

In the two strongest El Niños on record, 1982-83 and 1997-98, that has meant relentless storms pelting California.  With storms comes precipitation and as we all know CA is in desperate need of rain, snow or both.

Why do very strong El Niños bring more rain to California?

El Niño can bring something to Southern California called the subtropical jet stream. This current of air usually runs over the jungles of southern Mexico and Nicaragua, a reason Central America has rain forests.

However – El Niño needs to be particularly powerful to affect Northern California and there is evidence that our current El Nino is not strong enough yet.  The really big El Niños can soak the whole state. But right now, it’s possible to get a lot of flooding and mudslides in the south. In Northern California, you could get below-normal rainfall and snowpack.

This why experts are hesitant on calling this a drought-buster yet.  But if the El nino pattern further strengthens we could get lucky enough to have a silver bullet that pulls the state out of one of the worst droughts in history.