El Niño, the warm phase of the El Niño-Southern Oscillation, can interact with the polar vortex in complex ways. During a strong El Niño, the polar vortex may weaken, allowing cold air to spill into regions like the northern United States. However, experts note that the polar vortex is only one piece of a larger puzzle, and its influence on long-term winter patterns is limited, especially during strong El Niño events.