Driven by higher-than-normal Pacific Ocean water temperatures, an El Nino weather pattern has been building in strength since March, but its impacts will vary from one region to another.

“What’s new this month is that this could be one of the strongest El Ninos” since 1997, said Mike Halpert, deputy director of NOAA’s Climate Prediction Center in College Park, Md., during a monthly update on the El Nino Southern Oscillation weather pattern that was held Aug. 13.

Halpert emphasized that predicting how El Nino could affect storm systems along the West Coast and in regions such as the Columbia River Basin is difficult, largely because it is not the only influence on weather.

“If it was the only driver we could say a lot more than we can,” Halpert said. “El Nino is certainly different things to different people in different places.”

NOAA forecasters declared that a weak El Nino had developed in March, prompting an advisory to be issued that remains in effect. A July update predicted the weather pattern had strengthened and will likely last into early next spring. Strong El Nino events are characterized by Equatorial water temperatures that are at 1.5 degrees Celsius above normal for three months.

Halpert said that temperature benchmark could reach or exceed 2 degrees above normal, something that has happened only three times in recent decades.

Generally, it is expected that this will lead to below-normal precipitation and higher-than-normal temperatures across the Columbia Basin and Canadian border states to the east through next spring. By contrast, El Nino could produce higher-than-average rain and snow in California and in Southwestern states, but it was noted that any increased precipitation due to El Nino is unlikely to make up for a four-year drought in California.

The broad-brush El Nino forecast for the Columbia Basin is not a good one, considering there could be conditions that might match or exceed this year’s conditions — above normal temperatures that led to a “snow drought” across the region. While overall precipitation was close to average, there was a remarkably early snowpack melt and runoff, with river flows and temperatures that are normally seen in August arriving in July.

“The real message is that it’s likely to be a strong event,” Halpert said of the El Nino pattern that will persist into next spring. And because it is expected to be a strong pattern, predicted impacts will “tend to be more reliable.”

However, Halpert said that even with a strong El Nino, predicting impacts from it still amounts to uncertain long-range weather forecasting.

“It’s important to remember that just because something is favored (by forecasting models), doesn’t mean it will necessarily happen,” Halpert said, referring to the varied effects that could result from one region to the next.

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