El Niño's impacts are most noticeable during the northern hemisphere winter. It typically brings warmer, wetter conditions to the eastern Pacific, drier weather to the Amazon, and warm, dry conditions to Indonesia. In North America, El Niño weakens the polar jet stream, often splitting it into a more active southern branch. This can lead to cooler, wetter conditions in the U.S. Sunbelt, drier weather in the Ohio River Valley, and warmer conditions in the Pacific Northwest and parts of Canada.