Understanding what's El Niño mean for North American weather

A developing climate phenomenon is continuing to grow and could have profound effects on weather patterns across North America this autumn and winter. The naturally-occurring climate event involves trade winds over the Pacific Ocean weakening or reversing, allowing warm water to spread eastwards. This releases heat into the atmosphere and drives major shifts in global weather systems. Understanding what's El Niño mean helps explain why meteorologists are closely monitoring these changing ocean temperatures.

The eastward shift of warm ocean waters can cause the Pacific jet stream to move south and extend eastwards, directing rain-bearing weather systems across the southern United States. South-eastern states, including Florida, Georgia and the Carolinas, face a greater chance of seeing above-average rainfall. California could also experience a wet winter, with authorities preparing for anticipated floods and mudslides, while coastal areas face risks from rising sea levels driven by Kelvin waves.

El Niño winters typically bring southern rain and drier northern conditions across North America.

Conversely, the shift of the Pacific jet stream generally leads to warmer and milder winters in the north-west United States, Northern Plains, Ohio Valley, and parts of Canada. This reduces the risk of flooding, but reduced rainfall can leave groundwater and river levels low, potentially fueling drought and wildfires in the spring and summer months.

While long-range forecasts from agencies like the US National Weather Service suggest these outcomes are likely, no two events are identical. The phenomenon does not guarantee specific weather conditions everywhere, but rather shifts the odds in favor of certain outcomes. Evidence also suggests it can increase the likelihood of disruption to the stratospheric polar vortex, which may bring snowfall later in the winter season.

Why it matters These shifting climate patterns alter regional water supplies, flood risks, and wildfire hazards across the United States and Canada. While southern regions prepare for heavy rain and potential flooding, northern areas must monitor drought conditions and water levels.