Icicles hang on branches of a bush on the banks of the River Elbe in Dresden, eastern Germany, Thursday Feb. 2, 2012. (Norbert Millauer/DAPD)

Unofficial low temperatures recorded in major European cities, since Jan. 31 (Meteo-France, Austrian Weather Service, NOAA, weather.com)

In the mountains of Serbia and Bosnia, some 11,000 villagers remain stranded in their homes after several weeks of heavy snow made roads all but impassable. With over 2 meters (6.5 ft) of snow on the ground, emergency helicopters have begun to airlift food supplies and evacuate villagers in need of medical care. The BBC reports that snow fell across the region almost daily since early January, with more expected over the weekend.

View Photo Gallery: Dozens of people have died in a cold snap across Eastern Europe, authorities said Tuesday. Some countries have called in the army to help secure food and medical supplies and set up emergency shelters for the homeless.

A girl looks out of a window covered in frost on a bus moving in heavy snow in Belgrade, Serbia, Friday, Feb. 3, 2012. Fresh heavy snow has triggered traffic chaos in Belgrade and other Serbian cities, further complicating relief efforts as Eastern Europe's harshest cold snap in decades spreads to the north of the country. (Darko Vojinovic/AP)

While the core of the arctic air has been centered over eastern Europe, few parts of the continent have escaped winter’s icy grip. In Italy, forecasters have called it the coldest week in 27 years, as widespread snow disrupted transportation across the northern and central part of the country. (AccuWeather reports heavy snow in Rome this morning) Snow even fell as far south as the Mediterranean island of Corsica, where some locations recorded over 20 cm (8 inches).

Farther north, canals have lent themselves to ice skating in the Netherlands, and in northern Germany, the Elbe River has started to freeze over.

What’s causing the extreme cold?

Typical jet stream patterns for the positive (top) and negative (bottom) phase of the North Atlantic Oscillation (NAO) (NOAA)

Occasionally, these two pressure systems weaken simultaneously, allowing a dome of cold Siberian air to drift westward into Europe and North America (bottom right image).

When arctic air plunges into the mid-latitudes for an extended period, it usually means that the Arctic Oscillation (AO) and North Atlantic Oscillations (NAO) are both in their negative phases (also illustrated to the right). Currently, however, these two patterns are not in sync: the AO is negative, but the NAO remains positive. The result is that Europe and Asia have experienced extreme cold, while most of North America has seen an unusually warm winter.

People walks on an ice covered dam next to frozen Black Sea waters in Constanta city, some 230km east of Bucharest on February 1, 2012. Temperatures plunged to minus 34 Celsius in central Romania. (DANIEL MIHAILESCU/AFP/GETTY IMAGES)

Frigid conditions are expected to remain in place into early next week, with the core of the cold parked over Western Europe this weekend. The UK Met Office is forecasting possible snow showers in the eastern UK as a low pressure system arrives from the west. In central and eastern Europe, temperatures have slowly begun to rise, but will stay below freezing, some 5-10ºC below average.


Wintry weekend forecast for the UK (UK Met Office)

Vivid accounts of the cold from Eastern Europe (BBC)


Cold spell slams Europe (CNN)

Europe grapples with deep freeze (BBC)