Iceland Logs Record 19.8°C Christmas Eve, as Foehn Winds and Warm Seas Amplify Winter Heat

Rain fell in sheets on the corrugated metal roofs of Seyðisfjörður as families laid out their Christmas Eve dinners. Children went out in light jackets instead of snowsuits. In the narrow East Iceland fjord, where December usually brings snow and storms, the temperature climbed past what many residents initially assumed was a faulty reading.

By late on Dec. 24, the thermometer at the town’s automated weather station had reached 19.8 degrees Celsius (67.6 Fahrenheit) — the highest temperature ever recorded in Iceland in December.

The Icelandic Meteorological Office later confirmed the figure as a new national record for the month, edging past the previous mark of 19.7 C, set on Dec. 2, 2019, at Kvísker in southeast Iceland. Another station in Bakkagerði, a small settlement in Borgarfjörður Eystri on the east coast, also hit 19.7 C on Christmas Eve, matching the old record and underscoring that the heat was not a single-station fluke.

For a country where average December temperatures typically hover between minus 1 C and plus 4 C (30 to 39 F), the nearly summerlike warmth in the dark of winter stood out.

“This is unbelievable warmth,” Icelandic meteorologist Einar Sveinbjörnsson wrote on Facebook, using the Icelandic phrase “Þetta eru lygileg hlýindi.”

He said a second station in Seyðisfjörður, at Vestdalur above the town, registered a maximum of 19.4 C. “There is no obvious reason to doubt these measurements,” he added.

The readings were subjected to routine quality checks, but the meteorological office found no errors. By the end of December, the agency and Iceland’s public broadcaster had adopted the 19.8 C value as the official national December record.

What caused the spike

The event was remarkable but not inexplicable. Meteorologists describe it as the result of a familiar local wind pattern known in Icelandic as hnjúkaþeyr — a type of foehn wind that can suddenly raise temperatures on the leeward side of mountain ranges.

A strong area of high pressure over the North Atlantic, to the east of Iceland, funneled unusually warm, moist air northward from lower latitudes in the days before Christmas. As that air mass hit Iceland’s highlands from the south and southeast, it was forced up over the mountains, where it cooled and shed moisture as cloud and precipitation. On the fjorded east coast, the air then descended and warmed through compression, sometimes dramatically, as it rushed down toward sea level.

“Monthly temperature records are usually set under exactly these kinds of conditions,” said Birgir Örn Höskuldsson, a meteorologist at the Icelandic Meteorological Office. A strong, warm air mass overhead and powerful winds interacting with the topography can turn certain valleys and fjords into temporary heat traps.

A warmer backdrop

What made this hnjúkaþeyr episode stand out, scientists say, was the backdrop against which it occurred: an atmosphere and ocean already running unusually warm.

The Arctic has warmed more than three times as fast as the global average over recent decades, according to the World Meteorological Organization and the annual Arctic Report Card produced by the U.S. National Oceanic and Atmospheric Administration. That assessment found the 12-month period from October 2024 through September 2025 to be the warmest such “water year” in the Arctic record, with the last decade the region’s hottest on record.

At the same time, the North Atlantic has been in an almost continuous state of marine heatwave since 2023. Sea surface temperatures across large parts of the basin have repeatedly hit record or near-record levels, with scientists describing the ocean as “running a fever.”

That excess heat in the ocean and atmosphere does not cause any single weather pattern on its own, but it raises the ceiling on how warm events like Iceland’s foehn winds can become.

“In the historical climate, a setup like this might have brought a mild spell into the low teens Celsius,” said one North Atlantic climate researcher who was not involved in the Icelandic measurements. “Now, with warmer seas and a warmer Arctic, the same pattern can push temperatures close to 20 degrees even in late December.”

Signs of change on land and at sea

The Christmas Eve spike was the latest in a string of unusual warm events in Iceland. In May 2025, the country experienced an early-season heatwave, with the station at Egilsstaðir Airport in East Iceland reaching 26.6 C (79.9 F). Several long-running observation sites set new May records during that episode.

Longer-term changes are also showing up in ecosystems. In autumn 2025, entomologists confirmed that mosquitoes had been found breeding in Iceland for the first time, ending its status as one of the world’s only mosquito-free locations. The species identified, Culiseta annulata, is adapted to colder climates, but researchers linked its successful establishment to a combination of warmer summers and milder winters.

Offshore, warmer seas have encouraged northward shifts in fish species such as mackerel, contributing to tensions over fishing rights between Iceland and neighboring countries in recent years.

Local risks beyond the thermometer

For residents of Seyðisfjörður, the idea of a changing climate is not abstract. In December 2020, days of heavy rain triggered destructive mudflows and landslides on the steep slopes above the town, destroying or severely damaging dozens of houses. The entire community was evacuated, and some residents did not return until late 2021, after extensive mitigation works.

Those same steep slopes help set the stage for hnjúkaþeyr events when winds blow from the right direction. On Christmas Eve 2025, forecasters also warned of gale-force winds and heavy rain in parts of East Iceland, even as the temperature surged.

The combination of warmth, wind and precipitation underscores the multiple hazards that can accompany such events, officials and scientists say. Sudden thawing and strong rain can destabilize snowpacks and saturated soils, increasing the risk of avalanches and landslides in some conditions, even if no major incidents were reported during this particular warm spell.

What it does — and doesn’t — prove

International media attention to the record has sometimes veered toward hyperbole, with some commentators calling it one of the most extreme events in climate history. Icelandic meteorologists have pushed back on that framing, stressing that strong foehn events have always punctuated the country’s winters.

They also emphasize that a single record cannot, by itself, prove the influence of human-caused climate change. Formal attribution studies, which run detailed climate model simulations to quantify how much global warming has altered the odds of specific events, would be needed to put numerical bounds on the role of greenhouse gas emissions in this case.

Still, most climate scientists say the pattern is clear. As the Arctic continues to warm and the North Atlantic remains unusually hot, winter heat records in high-latitude regions are becoming easier to break.

For Seyðisfjörður, that means the spectrum of “normal” December weather now spans from damaging landslides in one year to springlike warmth in another.

On the town’s Christmas Eve weather charts, the red line of 2025 now sits far above the pack of previous years. For many Icelanders, it serves as a visible marker of a climate in transition — less a one-off anomaly than a sign of what future winters may bring.