Meteorologists were reversing course on predictions that the La Niña weather anomaly is on its way out. Defying earlier patterns that showed La Niña was breaking down, forecasters warn the cycle will return for a rare third year in a row, bringing with it more weather risks for crops across the globe.
The U.S. Climate Prediction Center (CPC) said in its latest forecast that the outlook hints at “a re-strengthening of La Niña conditions again in the fall and upcoming winter.” The agency gives a La Niña return between November and January a 61% chance, up from 53% in April. Forecasters also say La Niña has a 59% chance of continuing through the summer, and up to a 55% chance of persisting through the fall. Most other global climate model predictions also expect the anomaly will weaken over the summer and strengthen in the fall. The current La Niña cycle began in October, following a previous cycle that lasted from the fall of 2020 until the summer of 2021.
For those not familiar, La Niña (meaning “little girl” in Spanish) and its counterpart El Niño (“little boy”) are phases in what is called the El Niño Southern Oscillation, or ENSO. The Southern Oscillation is a change in air pressure over the tropical Pacific Ocean. When coastal waters become cooler in the eastern tropical Pacific (La Niña), the atmospheric pressure above the ocean increases. Conversely, El Niño marks the warming phase of the cycle. Between them is a neutral phase, which is what forecasters had thought we were headed toward this spring.
The La Niña weather pattern has occurred three times straight only twice since the 1950s, in 1973–1976 and 1998–2001. During a La Niña event, the changes in Pacific Ocean temperatures affect the patterns of tropical rainfall from Indonesia to the west coast of South America. These changes in tropical rainfall patterns affect weather patterns throughout the world. These effects are usually strongest during the winter months when the jet stream is strongest over the United States. While not every La Niña is the same, the Pacific Northwest is typically wet in fall and winter during La Niña, while much of the South, from Southern California to the Southeast coast, tends to be dry.
More than half the contiguous U.S. is currently experiencing drought, which has only worsened the past three months across much of the Southwest and central to southern Great Plains. According to Brad Pugh, a drought expert at the NCPC, the start of the widespread severe to exceptional drought across the Southwest was due to the failed 2020 monsoon. In fact, the 2020 monsoon season was the driest and warmest on record for the Southwest. Pugh says the persistence and additional expansion of the drought during the past two years are related to the consecutive La Niña winters, which typically favor below-normal precipitation and above-normal temperatures across the southern tier of the U.S.
The moderately strong La Niña in April also influenced precipitation patterns across the northern half of the U.S. but with the opposite effect. Overly wet conditions and cooler than normal temperatures across the northern tier has led to overly wet conditions that have delayed planting in several states. Too much moisture and flooding could be a problem in parts of the south later this year as a potentially persistent La Niña also mean another active Atlantic hurricane season. Since La Niña first intensified in late summer 2020, the past two hurricane seasons have generated 51 total storms, 21 of which became hurricanes and 19 of which made a mainland U.S. landfall.
Internationally, another year of La Niña could also spell trouble for other global crops. Generally, Southeast Asia, South Africa, India, and Australia receive above-normal rainfall, and drier weather is seen in Argentina, Europe, and Brazil. The La Niña event has already led to considerable yield losses in grain and oilseed crops in Brazil and Argentina in both marketing years 2020-21 and 2021-22. Meanwhile, a second year of severe La Niña-induced flooding in Australia has decimated livestock producers and dairy farmers in the eastern part of the country, which includes enormous equipment and infrastructure losses. (Sources: NOAA, CPC, Accuweather, Wunderground)