The National Oceanic and Atmospheric Administration (NOAA) has officially declared that a La Niña weather pattern is currently underway. This cooler climate event, part of the El Niño Southern Oscillation (ENSO) cycle, is expected to be shorter and weaker than traditional La Niña occurrences. Nevertheless, it will still have implications for global weather and climate conditions.
La Niña is characterized by cooler-than-average sea surface temperatures in the tropical Pacific Ocean. The ENSO cycle, which includes both El Niño and La Niña phases, typically operates on a multi-year basis, alternating between warm and cold periods every two to seven years. The conditions for this unusual La Niña began to materialize in December 2023 and are projected to last until April 2024.
According to NOAA, sea surface temperatures had remained close to average since April 2023. However, temperatures dipped below the necessary threshold for La Niña in December, marking its official onset. To qualify as a La Niña event, these temperatures must fall 0.9 degrees Fahrenheit (0.5 degrees Celsius) below the long-term average and remain there for five consecutive seasons.
NOAA's computer models indicate that this La Niña will continue to keep temperatures below the threshold into the spring. NOAA representatives noted, "There's a 59% chance La Niña will persist through February–April, followed by a 60% chance of neutral conditions in March–May."
Interestingly, this La Niña developed later than anticipated and did not have sufficient time to strengthen before the onset of winter. "While she's dragged her heels, all the pieces came together this past month," remarked NOAA representatives, highlighting the unusual nature of this occurrence. Researchers remain uncertain about the reasons behind the delayed development, although warmer-than-average ocean temperatures in early 2024 may have played a role.
La Niña events generally influence weather patterns significantly. For instance, they tend to increase hurricane activity over the Atlantic and cause distinct winter weather variations across the United States. During a typical La Niña, northern regions including parts of the U.S. and Canada experience colder and wetter winters, while southern states tend to enjoy warmer and drier conditions.
The current La Niña has emerged following a period of record-breaking heat attributed to an El Niño that affected global temperatures in 2023 and early 2024. This transition from El Niño to La Niña aligns with historical patterns but has raised questions among researchers regarding the predictability of such climate shifts.
To aid in understanding these phenomena, NOAA has created a flowchart detailing the stages that determine when a La Niña is officially recognized. They emphasize that predicting the duration of a La Niña event remains challenging. "There's a reason our flowchart says 'the next several seasons' instead of providing a specific number: we can make predictions, but it's impossible to know ahead of time exactly how long La Niña conditions will last," added NOAA representatives.
