It may translate to “the child,” but this year’s El Niño is shaping up to be anything but child-sized, according to meteorologists’ observations. As the cyclical weather phenomenon increases in strength, what could it mean for us?
A disruption of standard weather patterns, El Niño refers to a warming of water in the eastern Pacific Ocean that occurs once every two to seven years. When this happens, the tropical rainfall that usually hits places like Indonesia and Southeast Asia occurs farther east instead, changing the direction of the jet stream as it flows over North America. “The wind patterns at jet stream level across the Pacific Basin are strongly controlled by rainfall patterns across the Pacific,” said Gerry Bell, a meteorologist. “By shifting those rainfall patterns, it also affects the winds and the jet stream, and that’s how the weather over the U.S. is impacted.”
Specifically, warm water and resultant precipitation in the eastern Pacific causes the North American jet stream to move farther south than it usually flows. As a result, moisture that usually enters the United States from Washington state or British Columbia instead enters through California. “There’s a southward shift in the storm tracks and in the main winter precipitation,” Bell said. “As a result, more of the southern U.S. has above-average precipitation, while the northern U.S. has below-average (precipitation).” But while El Niño may be a semi-regular occurrence for the United States, this year’s pattern is anything but.
Through the years, El Niños tend to vary in strength; the last peak was in 1997-98. This time around, all indications again point to a stronger-than-normal pattern that could persist well into next spring. That’s backed by a report published by NOAA last month, which states a “greater than 90 percent chance” that El Niño will persist through the 2015-16 winter, with “around an 85 percent chance” it will last into early spring 2016. “At this time, the forecaster consensus unanimously favors a strong El Niño,” the report concluded.
So what does that mean for the West? First and foremost, Bell said, it means there will probably be more snowfall, from the Sierra Madre Range in Wyoming to the Sierra Madre Mountains in California. “The whole intermountain region tends to have a lot more snowfall because you have more precipitation,” he said. “It depends exactly where that jet stream is lining up, but central Wyoming, southern Wyoming, Colorado, Utah, western Nebraska – that whole area tends to have above-average snowfall with El Niño.”
Richard Emanuel, a meteorologist with the National Weather Service in Cheyenne, agreed with that assessment, adding that El Niño patterns also tend to make southeast Wyoming winters a little warmer, albeit not enough to turn the snow to rain. “Just because it’s warmer doesn’t mean it’s going to be warm,” he said. But Emanuel noted that El Niño isn’t a standalone phenomenon, and there are many factors that could change how it impacts” this region Emanuel said. “In the absence of other factors, El Niño years tend to produce somewhat warmer-than-average conditions here, though there are exceptions.” For example, he said, there’s something called the North Atlantic Oscillation that can bring colder air down out of Canada, which may enhance any warming effects El Niño has on Wyoming.