Weather stations across Iceland recorded temperatures in excess of 15°C on Wednesday afternoon and evening. Temperatures moving up to 13 degrees above the long-term average these days also occur, for example, beyond the Arctic Circle in the north of Scandinavia or in Greenland.
“The highest temperature, 19.7 °C, was measured – tentatively – at Bakkagerði station on the east coast of Iceland. If this temperature is confirmed, it will equal the absolute December record from 2019 from the Kvísker station,” the Czech Hydrometeorological Institute reported on social media.
The cause of the extremely high temperatures in Iceland is the unusual arrangement of pressure formations over the European continent. Over the eastern Atlantic and part of northern Europe there is a massive high pressure area, on the back of which very warm air flows from the southern directions, which reaches far to the north. In addition, the warming in some places of the subpolar island amplifies the so-called hair dryer effect, which occurs in the lee of the mountain ranges.
The principle of the hairdryer effect
A warm and dry dry wind occurs under conditions where the flow has to overcome a high mountain massif (for example, the Alps). With forced ascent, the air cools by 1 °C for every 100 meters of altitude until it is completely saturated with water vapor. When clouds form at a certain level, this saturated air cools by only 0.6 °C per 100 meters. The reason for this is the fact that moist air releases a small amount of heat into the atmosphere and thus warms up slightly in return.
While it can rain heavily on the windward side of a mountain barrier, this air dries out and begins to descend into the valley in the lee of the ridge. After the clouds have dissolved, it warms up again by 1 °C for every 100 meters of descent. Sunny and windy weather prevails in the lee of the mountains, with temperatures up to 10 °C higher than on the opposite side. The more humid the original air, the greater the temperature difference between the windward and leeward sides.
In recent decades, the frequency of significant temperature deviations around the world has been increasing in connection with ongoing climate change.
