Swedish Ice Service

Ice conditions in the Baltic
The Swedish coastal waters extend from approximately latitude 55N to latitude 61N with a significant temperature difference during winter, hereby also a significant difference in the ice conditions between Bay of Bothnia and southern Baltic.
Chart with easy/normal/severe ice conditions (Click to enlarge)

During a year with normal temperatures, a normal ice winter can be expected – provided that no exceptional conditions occur.
However, it must be stressed that there are other contributions to the actual ice condition; fluctuations in wind or temperature can improve (or deteriorate) the ice situation with respect to the normal also with a mean temperature close to the normal.
Consequently, an easy ice winter in Bay of Bothnia could be characterized as a strong ice winter in Skagerrak. Every ice winter thus must be compared to what normally can be expected in each sea area.
As mentioned above, the extent of sea ice is determined by the combination of temperature and wind conditions. The wind will make the ice more compact or more scattered and create conditions of great importance for winter navigation, such as ridging or ice pressure against coasts and ports.

Persisting northeasterly or easterly winds, wintertime generally associated with cold temperatures, will make the existing (and growing) sea ice drift towards the Swedish east coast. Areas of ridges will then form, difficult to force. Significant leads and open areas then form on the Finnish side. In situations with predominately westerly or southwesterly winds, easy ice conditions are likely on the Swedish side of the Baltic and Gulf of Bothnia while the ice becomes more compact further east.

Charts with freeze-up and break-up dates

(Click to enlagre picture)	(Click to enlagre picture)

On the contrary, southwesterly winds on the Swedish west coast means that slush or shuga may compact in the harbours. This may occur particularly during the short break-up period. Conditions on Skagerrak are slightly different, as ice from Kattegat will drift northwards with the coastal currents with deteriorating ice conditions as a result.