Sweden, like the rest of the Nordic countries, is accustomed to long, dark winters, with shorter days and longer nights due to their northern location.

But this December has been exceptionally gloomy and overcast in Stockholm, meteorologist Viktor Bergman at the Swedish Meteorological and Hydrological Institute (SMHI) told AFP.

"So far in December -- the month isn't over yet -- there's been only a half-hour of sunlight," he said.

"We've had unstable low pressure systems with mild and humid weather, and that brings lots of clouds. There hasn't been a chance for the skies to clear."

"The sun has also been weak, and its rays have not been able to clear away the clouds," he said.

The average amount of sunlight in Stockholm for the full month of December is around 33 hours, according to data compiled from 1991 to 2020, Bergman said.

He said the sun could make an appearance in Stockholm in the coming days, "but it's a little uncertain".

The darkest December ever recorded in the Swedish capital was in 1934, when the amount of sunlight was so minimal it was "rounded down to zero hours", Bergman said.

Other parts of Sweden have fared better this December, with the southeastern town of Karlskrona registering the most sunlight in the country so far, at 12 hours.

Stockholm has also had no real snowfall this winter, contributing to the sense of darkness as the reflection from snow on the ground helps brighten surroundings.

That does not look set to change, Bergman predicted, dashing Stockholmers' hopes of a white Christmas.

"It's looking very pessimistic for Christmas."