BY ISABELLA O’MALLEY
The National Oceanic and Atmospheric Administration’s Climate Prediction Center says there is a 60% chance that a weak La Nina event will develop this autumn and could last until March.
La Nina is part of a natural climate cycle that can cause extreme weather across the planet — and its effects vary from place to place.
Although there is no guarantee how this La Nina will play out, there are some general trends. Experts say northern parts of South America could see more rain than usual. Southern regions of the U.S. and parts of Mexico could be drier than average. The northern tier of the U.S. and southern Canada could be wetter than average.
La Nina is the cool phase of the El Nino-Southern Oscillation, a naturally occurring global climate pattern that involves changes in wind and ocean temperatures in the Pacific and can cause extreme weather across the planet.
These cold ocean temperatures and changes in the atmosphere affect the position of the jet stream — a narrow band of fast-moving air flowing from west to east around the planet — by bumping it northward. The jet stream sits over the ocean and can tap into its moisture, influence the path storms take and boost precipitation.
Cook noted that the frequency of La Nina events can be stressful for regions that have been dealing with drought lately, such as East Africa. “If we’re moving into another La Nina event, it means kind of a continuation of those really bad conditions.”
La Nina weather impacts
The influence La Nina has on the weather varies based on location and the season, said L’Heureux. Parts of South America, such as eastern Argentina, can be drier than average while Colombia, Venezuela and northern parts of Brazil can be wetter than normal.
“It depends exactly where you are. Part of that is because there’s a monsoon cycle, wet and dry season, that goes through Central America and South America, so La Nina is basically modifying the intensity and placement of those monsoon cycles,” explained L’Heureux.
In the U.S., the Northeast and Ohio Valley typically see wetter than normal conditions with an active storm track due to the position of the jet stream, said Samantha Borisoff, a climate scientist at NOAA’s Northeast Regional Climate Center based at Cornell University.
La Nina, El Nino and climate change
Scientists say the link between climate change and La Nina and El Nino is not entirely clear.
Paul Roundy, climate scientist at the University at Albany, said climate models tend to indicate more frequent El Ninos and less frequent La Ninas, but not all models agree. Computer models also struggle to separate normal variation in the El Nino and La Nina phases from climate change’s warming influence on the oceans and atmosphere.
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