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Understanding the North Atlantic Oscillation: Basics and Examples

June 17, 2026 · The Clime Team
Understanding the North Atlantic Oscillation: Basics and Examples

The North Atlantic Oscillation (NAO) is a climatic phenomenon characterized by fluctuations in atmospheric pressure between the Icelandic Low and the Azores High over the North Atlantic Ocean. These fluctuations significantly impact weather patterns across Europe, Greenland, northeastern North America, North Africa, and northern Asia. (britannica.com)

What Are the Phases of the North Atlantic Oscillation?

The NAO operates in two primary phases:

  • Positive Phase: During this phase, the pressure difference between the Icelandic Low and the Azores High is greater than average. This leads to stronger westerly winds across the North Atlantic, resulting in milder and wetter winters in northern Europe and the eastern United States. (climate.gov)

  • Negative Phase: Here, the pressure difference is smaller than average, causing weaker westerly winds. This often brings colder and drier conditions to northern Europe and the eastern United States. (climate.gov)

How Does the NAO Affect Weather in the United States?

The NAO's influence on U.S. weather varies depending on its phase:

  • Positive NAO: In this phase, the eastern United States typically experiences milder and wetter winters. The stronger westerly winds associated with the positive NAO bring more frequent and intense storms to the region. (climate.gov)

  • Negative NAO: Conversely, a negative NAO phase is often linked to colder and drier conditions in the eastern United States. The weaker westerly winds result in fewer storms and more frequent cold-air outbreaks. (climate.gov)

Can the NAO Be Predicted?

Predicting the NAO is challenging due to its complex nature and the various factors influencing its phases. While scientists monitor atmospheric pressure patterns to anticipate NAO phases, reliable long-term predictions remain elusive. (climate.gov)

How Does the NAO Relate to Climate Change?

Research suggests that the NAO may be influenced by climate change, with potential shifts in its phases affecting regional climates. However, the exact relationship between the NAO and climate change is still an area of active research. (britannica.com)

Examples of NAO Impact on U.S. Weather

  • Winter of 2010–2011: A negative NAO phase contributed to a particularly cold and snowy winter in the eastern United States, with significant snowfall in cities like New York and Washington, D.C.

  • Winter of 2015–2016: A positive NAO phase led to a milder and wetter winter in the eastern U.S., with above-average temperatures and increased precipitation.

Understanding the NAO is crucial for anticipating and preparing for its impacts on weather patterns, especially in regions like the United States that are directly affected by its fluctuations.

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Frequently Asked Questions