Michelle McKeown: The weather tug-of-war that shapes our winters

Understanding the North Atlantic Oscillation won’t stop Irish winters being chaotic, but it helps explain why they sometimes fall into familiar rhythms. And it reminds us that, while climate change is gradually reshaping global systems, natural variability still has plenty to say

Waves lash the pier at Rosscarbery, West Cork. Picture: Andy Gibson.

If the atmosphere over the North Atlantic had a personality, it would be that friend who can never quite decide what they want, swinging between moods with dramatic consequences for Ireland’s winter weather. This grand atmospheric seesaw is known as the North Atlantic Oscillation, or NAO, and while it may sound like something straight out of an atmospheric science lecture, it has a habit of creeping into everyday life. Whether we get storm-lashed evenings, crisp frosts or mild, soggy Christmases often depends on what phase this mighty oscillation is in.

At its heart, the NAO describes the pressure difference between two big atmospheric players: a low-pressure system over Iceland and a high-pressure system over the Azores. When the contrast between these two regions changes, it shifts the strength and position of the winds that sweep across the Atlantic. This, in turn, shapes the weather we experience here on dry (or not so dry) land. Think of it as the atmospheric equivalent of tightening or loosening a giant rubber band.