Behind the Forecast: What is the North Atlantic Oscillation?

LOUISVILLE, Ky. (WAVE) - The North Atlantic Oscillation is a large-scale weather pattern that impacts global weather.

Two of the most common weather features in the North Atlantic Ocean are the large area of high-pressure west of Portugal (known as the Azores or subtropical high) and the area of low-pressure over Iceland (known as the Icelandic or sub-polar low).

The North Atlantic Oscillation (NAO) depicts pressure changes between these areas.

The NAO’s influence on winter weather in North America and Europe is quite strong. The NAO can impact the location and strength of the North Atlantic jet stream - which influences the path of storm systems across the North Atlantic.

A stronger-than-average difference between the Azores high and Icelandic low leads to a positive NAO. A positive NAO means westerly winds dominate, allowing warmer air and more frequent and intense storms to travel across the Atlantic. With a positive NAO, the eastern United States and northern Europe typically see stormy, mild, and wet winters. In the southeastern U.S., warmer-than-average temperatures are likely.

A negative NAO is representative of a weaker-than-usual difference between the Icelandic low and the Azores high. Easterly and northeasterly winds are more prevalent, bringing colder air and weaker and fewer storms. A negative NAO typically leads to cold, dry, and quiet winters in Europe and the eastern United States; above-average snowfall is also possible across the eastern U.S.

For January and the start of February 2023, the North Atlantic Oscillation has been positive. It was negative right before the blast of Arctic air moved into Kentucky and Indiana in December of 2022, pushing highs into the single digits and lows below zero.

The NAOs just another of the factors meteorologists take into account when long-term forecasting.

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