The first half of this word, is, comes from Old Norse íss, which in turn has the same Proto-Germanic root as the English word “ice”. It’s featured in a number of other compound words like iskall (ice cold), isglass (frozen juice-based ice pop or ice lolly), and istapp (icicle).

Is is also used in some phrases and idioms, such as bryta isen (break the ice), ha is i magen (to keep your cool, but literally “to have ice in your belly”) and ingen ko på isen (this is short for det är ingen ko på isen så länge rumpan är i land or “there’s no cow on the ice as long as the buttock is on land”. A good English translation would be “the coast is clear”).

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Dygn, meanwhile, is a day, but more specifically a 24 hour period (as an aside, there is a rarely used word for this in English, too, nychthemeron, from an Ancient Greek term meaning “lasting a day and a night”). 

Similar words to dygn exist in Danish and Norwegian (døgn), and you would use it if you specifically wanted to refer to something lasting 24 hours – here’s an example:

Jag har varit vaken ett helt dygn! (I’ve been awake a whole day and night – for 24 hours!)

If you wanted to talk about a day more generally in Swedish you would use the word dag. Here’s that example from above again to show the difference in meaning:

Jag har varit vaken en hel dag! (I’ve been awake a whole day (from morning to evening)).

Staying awake for a full day isn’t particularly shocking or impressive, but telling someone you’ve been awake for a full 24-hour period would most likely spark their curiosity.

Anyway, back to isdygn. As you may have figured out, it refers to a 24 hour period of ice, or more specifically, a 24 hour period of temperatures below freezing.

Usually, it’s used to describe a nationellt isdygn or “national ice day”, which is defined as a 24-hour period running from 7pm to 7pm, during which all of Sweden’s weather stations record a maximum temperature no higher than -0.1 degrees Celsius. It can also be used to refer to a 24-hour period of temperatures below freezing in a smaller area, but this is less common.

This differs from a frostdygn, where the minimum temperature is -0.1C or lower in a certain area from 7pm to 7pm the next day.

There are usually around 100-150 isdygn in Norrland per year, while the coast of Skåne in the far south usually has around 10-20. National isdygn are less common, and in some years there aren’t any at all. Frostdygn happen much more often, with around 70 per year occurring in Skåne and 200-250 in Norrland.

Sweden’s recent cold snap represents the first national isdygn this season, and indeed the first national isdygn since 2021, when four were recorded. They’re most common around mid-February, so maybe there will be a few more before winter is over?

Example sentences

Vintrarna mellan 1988-1993 var mycket milda med inga nationella isdygn alls.

The winters between 1988 and 1993 were very mild with no national ice days at all.

Vi hade en mycket sträng vinter i 1984/85 med 25 nationella isdygn.

We had a very harsh winter between 1984-85 with 25 national ice days.

Villa, Volvo, Vovve: The Local’s Word Guide to Swedish Life, written by The Local’s journalists, is available to order. Head to lysforlag.com/vvv to read more about it. It is also possible to buy your copy from Amazon US, Amazon UK, Bokus or Adlibris.