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    • Are we in an El Niño or La Niña year? Here’s the difference
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    Are we in an El Niño or La Niña year? Here’s the difference

    Vaseline Posted on

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    Meteorologists are monitoring a strong weather event that could keep Arizona unseasonably warm and dry all winter.

    The National Weather Service has issued a La Niña watch, with a 60% chance that La Niña conditions will develop in November. If it occurs, climatologists predict La Niña will last from January to March.

    “We favor the arrival of La Niña conditions,” said Jon Gottschalck, chief of the operational forecast division at the National Oceanic and Atmospheric Administration.

    Although climatologists are confident that La Niña will occur within the next two months, they cannot be sure.

    “We are still a little ways away from this impact,” Gottschalk said. “We’re still waiting for these conditions to officially develop in the ocean and then the atmosphere has to respond.”

    Here’s what you need to know about the El Niño and La Niña patterns and how they affect Arizona’s weather.

    What is La Niña?

    La Niña, and its counterpart El Niño, are climatic events that are part of a natural cycle called the El Niño-Southern Oscillation, or ENSO. It represents the relationship between ocean temperatures and atmospheric conditions emanating from the Pacific Ocean.

    During a La Niña event, the trade winds that blow from east to west near the equator become stronger. Stronger winds push warm water from the eastern Pacific toward Asia, raising surface temperatures in the western Pacific. This shift brings up deep, cold waters in the central and eastern Pacific Ocean.

    Cool water drawn from the depths of the ocean due to the wind shift causes a chain reaction of weather events. Once the atmosphere responds to changes in ocean temperatures, tropical rain will typically increase in areas such as Indonesia, the Philippines and northern Australia.

    During La Niña, the Pacific Ocean typically experiences a weaker hurricane season, with a busier season in the Atlantic Ocean.

    More: La Niña could turn Arizona’s hot, dry summer into a warm, dry winter. What you need to know

    What does a La Niña winter look like? Is La Niña warm or cold?

    La Niña affects weather around the world, but its impact varies depending on the region.

    It tends to cause warmer and drier winters in the Southwest, central Rockies, Gulf Coast and East Coast.

    In the Pacific Northwest, New England and the Great Lakes regions, La Niña usually brings wetter winters.

    What would La Niña mean for Arizona weather?

    If La Niña conditions occur, Arizona will likely experience a drier and warmer winter, but scientists expect this to be a weaker event.

    “Typically in the Southwest, with La Niña as you go into fall or winter, temperatures are generally warmer than normal,” he said. “There is quite a strong signal during La Niña events of below normal precipitation in the Southwestern and Southern Plains.”

    NOAA recently lowered its probability of La Niña from 71% to 60% and predicts that extremely dry and warm conditions will not develop in the Southwest.

    “La Niña forms quite slowly, and the slower it forms, the less time it has to actually peak,” says Michael Crimmins, a climatologist at the University of Arizona.

    While it likely won’t be the driest or hottest winter on record, La Niña could still have negative impacts on Arizona.

    After an abnormally dry monsoon, Arizona’s soil and vegetation are drier. Winter precipitation that is not normal could further strain water supplies and worsen next year’s wildfire season.

    “We’re always dealing with drought, and a La Niña event on the horizon doesn’t mean any relief,” Crimmins said. “It most likely means continued deterioration or a slide into short-term drought.”

    More: Can forecasters predict the weather 90 days in advance? Why long-term prospects are so complicated

    Vaseline
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