What to expect from a strong El Niño

After last year’s bone-dry winter, Arizonans could get some much-needed relief with a strong El Niño pattern this winter — and a new report says that pattern is more likely than not.

The U.S. Climate Prediction Center says there’s close to a 70 percent chance that El Niño conditions will shape up this winter and a 65 percent chance for the fall. This comes as historic drought continues to plague the Southwest and water in the Lake Mead reservoir hovers a couple feet above shortage levels.

But as the chances of an El Niño increase, Arizona officials say we shouldn’t expect it to bail us out of the drought.

“Last year was pretty dismal. The odds are in our favor that this coming year won’t be that bad,” said Nancy Selover, state climatologist. “(But) we could be disappointed again.”

It could spell good news for Arizona — a strong El Niño combined with the

right atmospheric conditions usually means a wetter winter for much of the country’s southern half, including the Southwest. But if those conditions aren’t just right, El Niño could pass without bringing the rain and snow Arizona needs.

A “Godzilla” El Niño was supposed to bring heavy downpours during the 2015-16 winter. As the name implies, it was going to be huge. But it actually brought less rain to Arizona than any other “strong” El Niño pattern in the prior 60 years, according to data from the National Oceanic and Atmospheric Administration.

While El Niño can bring strong rain and snow, which are sorely needed in the midst of the current long-term drought, officials warn it isn’t a perfect indicator and say they continue to brace for intense drought.

“We always plan for drought,” said Charlie Ester, Salt River Project’s Surface Water Resources manager. “Any surprises we have are on the wet side, not on the dry side.”

El Niño — and its counterpart, La Niña — are terms given to weather conditions based on sea surface temperature in the eastern Pacific Ocean.

When sea surface temperatures in the Pacific Ocean rise above normal levels for a long period, it’s called an El Niño. Combined with the right atmospheric conditions, a jet stream will divide the U.S. horizontally and bring more storms to the southern portion.

La Niña, as you no doubt guessed, is the opposite.

A strong El Niño pattern alone doesn’t guarantee a wet winter for Arizona. Atmospheric conditions — highand low-pressure systems — need to coincide with the rising temperatures in order for a wet winter to occur.

“The first indicators tend to be the sea surface temperatures ... but you also have to have the atmospheric pressure; low pressure on our side of the Pacific and high pressure on the other,” Selover said.

If the jet stream falls too far north, Arizona will miss out on the rain and snow, she said.

“The storms are driven along the jet stream,” she said. “If the jet stream stays way north like it did last time we had El Niño, which was great for Colorado, (but) it didn’t come far enough down for the storms to catch us.”

Winters with an El Niño tend to be wetter, but it’s not guaranteed, especially as climate change continues to push the jet stream further north. So don’t count on this winter to break Arizona’s drought.

“I never hold my breath,” Selover said.

“Sixty-five percent or so (of El Niño patterns) have been above normal — that means there’s a fair number of nonproducers,” Ester said. “Right now, all they’re really predicting is that we’ll have warm water.”

El Niño’s warming conditions are sometimes conflated with climate change — the past four years were Earth’s hottest on record and 2016’s El Niño strong pattern likely contributed.

But the trend of increasing temperatures continues even in years without an El Niño. For example, 2017 was the warmest year without the effects of one.

Officials early this year warned of an intense fire season this summer. Their concern was in part due to the previous winter’s low snowpack levels. During the winter months, officials prefer to get snow rather than rain, because it will eventually melt and keep conditions moist leading up to fire season.

Missing out on that winter snow means conditions are more dry and brittle. If an El Niño brings heavy rain, great, but snow is best, officials say.

“We’ll take anything we can get,” Selover said. “But we certainly prefer snow.”

As Arizona water managers vowed to have a Colorado River drought plan ready for the next state legislature to vote on, much of the attention is now on the river’s supply. Ester said the current drought is likely the worst in 700 years. Others place it closer to 1,200.

SRP’s reservoirs were 51 percent full Tuesday. Those levels show that planning for a drought works, he said.

That’s why water managers don’t count on a strong El Niño pattern. Ultimately, it doesn’t mean much without the right atmospheric conditions bringing storms to the jet stream.

“We can be optimistic ... but I don’t think there’s anyone around here that’s going to say, ‘Oh, good, a wet winter’s on the way,’ ” Ester said. “The important thing to remember is El Niño isn’t the only way to get a wet winter.”