Forecasts call for strong El Nio this winter, what it means for Southern California & drought

“It’s going to seem unusual because we haven’t seen a good winter since 2010-2011, that’s almost five years ago,” says Alex Tardy, a meteorologist with the National Weather Service in San Diego. He’s talking about the recently released long term forecast for the upcoming winter, it’s going to seem “unusual” because the forecast calls for above average precipitation in southern California.

Winter seasons have seen less than average rainfall across most of the state for those last four years. The remaining seasons didn’t fare much better, which leaves reservoirs across the state of California emptier each day. More than 70 percent of the state remains in the “extreme” category of drought or worse, needing about 2 whole extraseasons of rain to make up for the deficit.

For southern California help seems to be on the way. Temperatures have been above average since the summer of last year in the region where El Nio conditions are monitored, but recently numbers have sky rocketed, similar to those during the warm up before the mega El Nio in 1997-1998.

“It’s really ramping up,” Tardy says. “We’re already declared El Nio as an existence, now we’re even making statements that a strong El Nio is the more likely scenario as we enter into the fall. And what that means is there’s a much greater probability of us seeing more rain than an average year normally provides to us in Southern California.”

El Nio is a build up of warm water in the normally cooler eastern equatorial Pacific Ocean. A ridge of high pressure that generally keeps winds easterly along the equator breaks down and the winds reverse direction, allowing the warm water out west to slowly move eastward. As the water temperature rises the atmosphere responds, generating more storms along the equator in the eastern Pacific and altering weather patterns around the globe, hurricane season included.

There have already been 5 named storms in what is expected to be a very busy season in the eastern Pacific. Three of those storms reached category four status as hurricanes. The second to last storm, Dolores (Tropical Storm Enrique formed a day later), sent southern California a much welcomed bath this past weekend, though the heavy rain did some serious damage. Warm water in the eastern Pacific ramps up the intensity and frequency of tropical cyclones, it also lets those storms and their remnants move farther north along the coast before weakening. On the contrary, the Atlantic hurricane season is expected to be below average, typical of El Nio years.

Aside from tropical weather, El Nio really makes its presence felt during the winter season. “Typically when you see an El Nio, especially a strong one, you start the season off pretty quickly,” Tardy explains, “and the difference between El Nio and normal winters is not just large storms; large storms can occur anytime of the year, any winter El Nio or not. It’s the storms that we see that come in frequency, so one after another, and that’s what we’re looking for November/December. Now the key will be can we sustain this into February and March.”

The key for the drought is that extended spring rainfall for the entire state. Strong El Nios (El Nios with a temperature anomaly above 1.5 C) have a pretty good track record delivering above average rainfall to southern California, but the rest of the state isn’t as consistent. The Central Valley and northern California, where rain is most needed, may not see their grass turn any greener.

“We need the whole state to be hosed down. So we need the whole state to see one to two, about one and a half to two seasons of precipitation, so that’s our deficit,” Tardy continues. “We’re looking at one and a half to two seasons statewide of missing precipitation in the past four years, so we need to have not just a normal year statewide, we need to have two times of a year statewide.”

But that much rain can cause big issues as demonstrated by last weekend’s deluge. Residents who have spent only the last few years in California may be too complacent.

“So any year we should be thinking about flood insurance before the winter and flood preparedness and ramping up to it, but this year it’s going to seem unusual,” Tardy explains. “It’s time now to start thinking about if there is anything I need to do come the fall because it’s going to be too late if you wait until November/December.”

So how good is the outlook? The Climate Prediction Center just released a few long term forecasts that put southern California in a 40 percent chance for above average precipitation from September through November. 40 percent may not sound like much, but considering how far away that time period is it’s a good vote of confidence. Even better, the winter outlook gives Southern California a whopping50 percent chance for above average precipitation. But again, there’s that same problem, southern California. Central California is only looking at a slight chance for above average rainfall while the rest of the state is looking at an equal chance for below, average, and above average rainfall this fall and winter.

“So we won’t get ahead of ourselves right now. We’re not going to say the drought is going to be washed out,” Tardy says, “but we are going to say, at least for Southern California, it does look like a wet winter.”