Climate experts have issued warnings of winter heatwaves and, in some areas, a “winterless Christmas” due to unusually high winter temperatures in the United States and parts of Europe. Temperatures above historical averages in the days leading up to the holiday, with daytime highs in many US regions reaching up to 20°C above average for late December. Similar abnormalities were noted throughout Europe, highlighting how heatwaves grip the US and Europe during a season often marked by winter storms, cold, and snow.

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Persistent high-pressure ridges in the upper atmosphere are thought to be the immediate cause of the warming. Warm air is trapped close to the surface by these systems, allowing temperatures to rise over several days. However, scientists emphasize that the intensity and frequency of these events have significantly increased due to long-term warming driven by greenhouse gas emissions. The US and Europe have historically contributed significantly to these emissions, connecting decades of fossil fuel consumption to the extremes of today.

Record-Breaking Warmth Across the United States

• The week before Christmas, daytime temperatures across much of the United States were 15–25°F (8–14°C) above average.
• Anomalies of up to 35°F above average were noted in some places.
• Nationwide, several daily temperature records were surpassed.
• It was the warmest Christmas season the nation had ever seen, according to meteorologists.

Large areas, from the West and Plains to the Midwest and Southeast, were impacted by abnormally warm air, according to Peter Carter of the Climate Emergency Institute. WFLA-TV chief meteorologist Jeff Berardelli referred to the warmth as “off the charts,” citing data that showed widespread record highs through Christmas. A powerful upper-level ridge created the phenomenon, sometimes called a “heat dome,” which suppressed precipitation and cloud formation while causing air to sink, compress, and warm. As heatwaves grip the US and Europe, these winter heat domes are blurring the traditional seasonal divide, with conditions resembling late spring rather than mid-winter.

In its December forecast, the US National Oceanic and Atmospheric Administration (NOAA) also noted the anomaly, predicting above-average temperatures across most of the continental US from late December to early January. Forecasters cautioned that springtime conditions would be further reinforced by the absence of precipitation that accompanied the temperatures.

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Europe’s Winter Heatwave and Arctic Anomalies

• On December 24, 2025, Iceland recorded its highest-ever December temperature of 19.8°C.
• Warm air was carried far into the North Atlantic region by powerful south-westerly winds.
• Warmth was extended toward Greenland and Svalbard by high-pressure ridges.
• Meteorologists linked the incident to atmospheric blocking patterns.

Europe, on the other side of the Atlantic, had equally remarkable circumstances. The town of Seyðisfjörður recorded a temperature of 19.8°C in December, breaking the previous record set in 2019. Warm air, powerful winds, and steep terrain can cause rapid warming during downdrafts, setting the stage for record-breaking temperatures, according to meteorologist Birgir Örnölskuldsson.

Warm air was directed into the far North Atlantic by a strong south-westerly flow created by a strong ridge over northern and western Europe, according to independent forecaster Marko Korosec. Christmas Day was among the warmest on record in Iceland, the Faroe Islands, and even Svalbard due to this pattern. Although these ridges can happen naturally, scientists stress that their impact is increased by background global warming. As heatwaves grip the US and Europe, events once considered rare winter anomalies are becoming increasingly plausible, reinforcing concerns about how climate change is reshaping seasonal weather patterns in the northern hemisphere.

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