La Niña Expected to Impact US West Coast Weather: NOAA and WMO Forecast Changes

The National Oceanic and Atmospheric Administration (NOAA) has reported the development of a La Niña event, characterized by cooler-than-average sea surface temperatures in the central and eastern Pacific Ocean. This phenomenon is expected to influence winter weather patterns across the U.S. West Coast, bringing colder and wetter conditions to the northern regions and drier, warmer weather to the southern areas. NOAA forecasts a better-than-even chance of La Niña forming in the fall and winter of 2025, with probabilities exceeding 50% from September to November and increasing through the winter months.

La Niña is the cool phase of the El Niño-Southern Oscillation (ENSO) cycle, marked by cooler-than-average sea surface temperatures in the central and eastern Pacific Ocean. This cooling influences global weather patterns, typically bringing wetter and cooler conditions to northern U.S. regions and drier, warmer weather to the southern U.S., while also increasing Atlantic hurricane activity.

The 2020–2023 La Niña event was a rare "triple-dip" La Niña, lasting three consecutive years. This prolonged event led to numerous natural disasters, including intensified Atlantic storms and Western U.S. droughts, costing the U.S. over $252 billion in hurricane damage alone. Unlike previous triple-dip La Niña events, the 2020–2023 event was not preceded by a strong El Niño, challenging existing theories about ENSO cycles.

During La Niña events, the Pacific Northwest, including states like Washington and Oregon, typically experiences cooler and wetter winters. This can lead to increased snowfall, benefiting water supplies and winter sports industries. For instance, during the La Niña winter of 1998–1999, several ski resorts in the Northwest registered record snowfall, with Mount Baker in Washington setting a world record for the highest annual snowfall.

Conversely, Southern California often faces drier and warmer conditions during La Niña, exacerbating drought risks and increasing wildfire potential. The 2021 La Niña contributed to one of California’s worst wildfire seasons, with over 2.5 million acres burned and 3,500 structures destroyed.

The economic impact of La Niña events is multifaceted. Agriculture can be significantly affected, with altered precipitation patterns influencing crop yields. Fisheries may experience shifts in fish populations due to changes in ocean temperatures and currents. Energy demand can fluctuate as heating and cooling needs change with temperature variations. Natural disasters, such as floods and droughts, often lead to increased insurance claims and disaster response costs. For example, the 2020–2023 La Niña event intensified Atlantic storms and Western U.S. droughts, costing the U.S. over $252 billion in hurricane damage alone.

The World Meteorological Organization (WMO) announced that La Niña conditions may return and start impacting global weather patterns from September 2025. La Niña is characterized by the cooling of the central and eastern Pacific Ocean, which can increase the risk of both floods and droughts, affecting agricultural production. Although neutral oceanic conditions have persisted since March 2025, forecasts now indicate a 55% probability of cooling to La Niña levels between September and November. Despite this shift, above-average global temperatures are still likely in many regions. The WMO emphasized the economic and humanitarian benefits of seasonal forecasts, noting they can lead to substantial savings in sectors like agriculture, energy, transport, and health, and can also help save lives through early preparedness and response measures.

Climate change is leading to rising air and ocean temperatures and changing precipitation patterns throughout the Northwest. Rising air temperatures are causing more precipitation to fall as rain rather than snow. Though the interaction between climate change and La Niña is not completely understood, the cooler temperatures that accompany La Niña could temporarily reduce the warming effects of climate change and cause more precipitation to fall as snow. Nevertheless, the La Niña events of today are trending warmer, reflecting overall increases in annual average ocean and air temperatures. As La Niña events warm, future events could record lower snowfall and more rainfall in the Northwest.

The developing La Niña event presents a complex array of challenges and opportunities for the U.S. West Coast. Understanding its potential impacts is crucial for effective preparation and response across various sectors. Continued monitoring and research will be essential in mitigating risks and leveraging any benefits associated with this climatic phenomenon.