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    • La Niña conditions could produce a dry winter for Southern California
    Washington

    La Niña conditions could produce a dry winter for Southern California

    Madoc Meredith Posted on

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    After one of the hottest and driest summers, Southern California could remain unusually warm and dry this winter as La Niña conditions develop, a cycle that can trigger erratic weather patterns worldwide.

    La Niña tends to produce drier weather in Southern California and the Southwest during the winter, a critical time for replenishing water resources. Drier vegetation can also increase the risk of wildfires.

    Even if this La Niña is weaker, it could still have severe regional impacts. Northern California could experience wetter than average weather this winter, according to the National Oceanic and Atmospheric Administration.

    While seven of the ten La Niña events this century resulted in dry years for California, research also suggests that the precipitation California receives will arrive in stronger storms, even as the overall climate becomes hotter and drier, which is what the Flood Risk Increased to the California Department of Water Resources.

    “California experienced record heat and drought this summer, drying out the landscape and throwing our hydrology into disarray before the water year even began,” said state climatologist Dr. Michael Anderson. “While there is still much uncertainty about what impact La Niña could have on the state this year, we know we can be confident that extreme conditions are taken into account.”

    Here’s what you should know about La Niña and what impact it could have on weather and conditions in Southern California and the Southwest:

    Will this be a La Niña year?

    The National Weather Service has issued a La Niña warning, with a 71% chance of La Niña conditions developing in October or November. If it does occur, climatologists predict La Niña will last from January to March.

    “We are supporting the emergence of La Niña conditions,” said Jon Gottschalck, chief of the National Oceanic and Atmospheric Administration’s operational forecast division.

    “Typically, temperatures in the Southwest with La Niña are generally warmer than normal early in the fall or winter,” he said. “During La Niña events, there is a fairly strong signal of below-average precipitation in the Southwest and Southern Plains.”

    La Niña results in below-average ocean temperatures in the Pacific, which can lead to erratic weather patterns across the United States and the world. A La Niña event could place even more stress on the heat and drought-stricken Southwest.

    What is La Nina?

    La Niña and its counterpart El Niño are climatological 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 in the Pacific Ocean.

    During a La Niña event, the trade winds that blow from east to west near the equator intensify. Stronger winds are pushing warm water from the eastern Pacific into Asia and warming surface temperatures in the western Pacific. This shift is resulting in deep, cold water in the central and eastern Pacific.

    Related: When does it start to cool down in California? That’s what Old Farmer’s Almanac predicts

    Cool water drawn in from the ocean depths by the wind shift triggers a chain reaction of weather events. Once the atmosphere responds to changes in ocean temperature, areas such as Indonesia, the Philippines and northern Australia tend to experience more tropical rainfall.

    “When that happens, these changes in tropical precipitation along the equator alter the jet streams in the Pacific and North America,” Gottschalk said. “These changes cause temperature and precipitation changes over the course of a season.”

    During La Niña, the Pacific Ocean tends to have a weaker hurricane season, while the Atlantic Ocean has a busier season.

    El Niño is the opposite condition as the trade winds weaken or sometimes reverse direction and sea temperatures rise. Warmer water releases more moisture and energy into the atmosphere, leading to wetter conditions in many areas and intensifying the Pacific hurricane season.

    Both patterns last nine to twelve months, but can last for years. They typically occur every two to seven years, but do not have a regular, predictable schedule. Historically, El Niño is more common than La Niña.

    There is a third ENSO pattern called the neutral phase. In neutral years without extremes triggered by El Niño or La Niña, trade winds and ocean temperatures tend to be closer to normal.

    While climatologists are confident that La Niña will occur in the next month or two, they cannot be sure.

    “We are still a little away from these effects,” said Gottschalk. “We are still waiting for these conditions to officially develop in the ocean and then the atmosphere will have to respond.”

    How will La Niña affect the weather?

    ENSO climate phases can influence weather across the U.S. and affect conditions in the coming winter months.

    According to Gottschalk, the Southwest, central Rocky Mountains, Gulf Coast and East Coast typically have drier, warmer winters during La Niña years. Northern California, the Pacific Northwest, New England and the Great Lakes regions could experience wetter winters during the event.

    But even if La Niña fully develops this year, climatologists say it’s difficult to predict what impact it could have on the weather.

    “La Niña forms fairly slowly, and the slower it forms, the less time it has to actually peak,” Crimmins said. “It looks like it’s going to be a weak event.”

    “These events have historically given us mixed conditions for the Southwest,” he added.

    The last La Niña began in 2020 and lasted until 2023, a rare event with three consecutive years of La Niña conditions known as the “triple dip” phenomenon. This event triggered droughts, floods, heat waves and other extreme weather events around the world.

    The Southwest was plagued by extreme drought and active wildfire seasons during this time.

    Although La Niña is unlikely to be as severe this winter as last, the extent of its impact is still uncertain.

    “That’s why you get this probabilistic forecast where it’s on the dry side, but it leaves the door open for average to above-average conditions,” Crimmins said. “I know it drives people crazy because they just want to know if it’s going to dry or not.”

    Hayleigh Evans writes about extreme weather and related topics for The Arizona Republic and azcentral.com. Email her with story tips [email protected].

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