There’s a high likelihood La Niña will affect the U.S. this winter, a weather pattern characterized by warmer, drier conditions across most southern states with increased precipitation and cooler conditions in other regions, according to the National Weather Service.
An El Niño weather pattern—La Niña’s counterpart—brought the warmest winter on record last year.
There is a 60% chance La Niña develops in the U.S. through November and persists through March, according to the latest projections from the National Weather Service.
La Niña is a climate pattern marked by cooler-than-average sea surface temperatures in parts of the Pacific Ocean and is the opposite of El Niño, which brings warmer-than-average temperatures.
Because of cooler sea surface temperatures, the jet stream—a current of air flowing from west to east—is pushed to the north, decreasing the odds of precipitation in the southern U.S. while increasing the chances of heavy flooding in the Pacific Northwest and Canada, according to the National Oceanic and Atmospheric Administration.
During a La Niña winter, temperatures are higher than average across southern U.S. states and cooler than normal in the north, NOAA said.
Emily Becker, an atmospheric scientist at the University of Miami, wrote in a blog for the NOAA that if La Niña does emerge this winter, it’s expected to be a weaker event that allows for more snow in the Northeast and central Plains.
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NOAA expects drier conditions in the Southeast, Southwest and some states in the Great Plains and Mountain West, including Utah, Nevada, Colorado, Wyoming, New Mexico and Oklahoma, between November and January. Above-average temperatures are also possible in the Southwest, Southeast and Mountain West, along with the Midwest, southern California and states along the East Coast.
The Pacific Northwest, Midwest and Northeast are expected to face above-average precipitation, according to NOAA. States with a higher chance of increased precipitation between November and January include Washington, Oregon, Idaho, Montana, Wisconsin, Michigan, Illinois, Indiana, Ohio, Pennsylvania and New York.
La Niña can also result in more severe hurricane seasons in the Atlantic Ocean by expanding the area of low vertical wind shear, which increases the number of hurricanes that develop and allows stronger storms to form.
Last winter—affected by El Niño—was the warmest on record in the U.S., with temperatures across the lower 48 states measuring 5.4 degrees higher than average, according to NOAA. Several states recorded their warmest winters ever, NOAA said, including North Dakota, Minnesota, Iowa, Wisconsin, Michigan, New York, Vermont and New Hampshire.
The La Niña and El Niño weather patterns are created by interactions between ocean surfaces and the atmosphere in the Pacific, and both occur about every three to five years, according to NOAA. Both weather patterns are part of the El Niño Southern Oscillation (ENSO), a climate phenomenon that emerges from a shift in winds and sea surface temperatures over the Pacific, though NOAA and the National Weather Service note their occurrence is not predictable. The agency previously warned climate change may increase the frequency of extreme El Niño and La Niña events with amplified rainfall and increasingly warmer temperatures. The two patterns don’t always follow each other, though it does happen. A La Niña that follows an El Niño winter typically results in warmer summers, and the National Weather Service warned earlier this year La Niña would likely result in record-breaking temperatures. The average La Niña pattern lasts about 15.4 months while El Niño typically lasts 9.5 months, though the longest La Niña on record spanned 37 months between 1973 and 1976.