Winter forecast takes shape; 'record strong' polar vortex forms

Key Points:

• The 2026 polar vortex started strong but has since weakened slightly, and a strong polar vortex generally leads to milder winters by keeping Arctic cold air contained.
• Forecasters are closely monitoring the historic El Niño event, which is expected to have a significant influence on winter weather, likely bringing milder conditions to most of the U.S.
• The interaction between El Niño and the polar vortex is complex and not fully understood; while El Niño can weaken the vortex and increase chances of cold outbreaks, this relationship can vary throughout the winter.
• El Niño is already impacting weather in the tropics, and its effects on higher latitudes, including stormier conditions on the U.S. West Coast, are expected to become more apparent from late autumn into mid-winter.
• Climate change is warming winters overall, meaning that even cold episodes today are milder than in past decades, which influences how seasonal factors like El Niño and the polar vortex affect weather patterns.