Ice observations

Ice observations and their coding

By the end of the 19th century, the national ice services of several countries bordering the North and Baltic Seas had introduced routine ice observing and reporting systems. The search for a suitable ice reporting code began very early because a quick and convenient way of transmitting the ice observations to a central body and making them available to users was urgently needed. Shipping traditionally has a large variety of terms designating the different ice phenomena, taking into account regional differences that are attributable to different natural environments.

Although today an essential criterion in the assessment of ice conditions still is the extent to which they hinder navigation, additional features describing the ice extent had to be introduced within the framework of the international exchange of ice information required in the wake of World War I. Requests for more and better ice information on the part of industry and shipping, efforts within the World Meteorological Organization to develop a uniform terminology, the transition to a prolonged shipping season lasting throughout winter in the Gulfs of Bothnia and Finland as well as increasing activities in the coastal areas forced the ice services to continually improve the technology and contents of their information exchange. The chronological data can be summarized as follows:

Chronological data

1920/21 National ice code

1st digit: ice conditions
2nd digit: impact on navigation

1928/29 1st Baltic Sea Ice Code

1st digit: ice conditions
2nd digit: navigation

1952 1st WMO Sea Ice Nomenclature

1954/55 2nd Baltic Sea Ice Code (revised in 1969, GTS use)

1st digit: (i): ice conditions
2nd digit (j): stage of ice development
3rd digit (k): navigational conditions

1968 2nd WMO Sea Ice Nomenclature

1980 WMO Ice Symbols

1981/82 3rd Baltic Sea Ice Code of 1980 (B = Baltic)

1st digit (AB) = quantity and arrangement of ice
2nd digit (SB ) = stage of ice development
3rd digit (TB) = topography and form of ice
4th digit (KB ) = navigational conditions

1955/56, 1981/82, 1993/94 Change of German station numbers

Baltic Sea Ice Code of 1980

The new code describes the ice conditions in harbours, fairways, coastal areas, and marked navigation channels. Together with the ice charts and detailed written ice reports, it informs ships' officers of current ice and navigational conditions. The sea and navigation districts of each country are designated by letters: AA, BB, CC etc. Each district is subdivided into sections numbered from 1 to 9.

The single observations for the code elements AB SB TB KB thus are compiled and distributed in the following general code format:


The fairway districts (AA, BB, ...) in the individual countries are sorted regionally from north to south and east to west, and the fairway sections (1,... 2,...) from onshore (harbour) to offshore (sea). The code numbers AB SB TB KB define the following conditions:

Code Tables for Reporting Ice Conditions (AB SB TB KB)

AB Amount and arrangements of sea ice

0 Ice-free
1 Open water - concentration less than 1/10
2 Very open ice - concentration 1/10 to 3/10
3 Open ice - concentration 4/10 to 6/10
4 Close ice - concentration 7/10 to 8/10
5 Very close ice - concentration 9/10 to 9+/10
6 Compact ice, including consolidated ice - concentration 10/10
7 Fast ice with ice outside
8 Fast ice
9 Lead in very close or compact drift ice or along the fast ice edge
/ Unable to report

SB Stage of ice development

0 New ice or dark nilas (less than 5 cm thick)
1 Light nilas or ice rind ( 5-10 cm thick)
2 Grey ice (10-15 cm thick)
3 Grey-white ice (15-30 cm thick)
4 White ice, first stage (30-50 cm thick)
5 White ice, second stage (50-70 cm thick)
6 Medium first year ice (70-120 cm thick)
7 Ice predominantly thinner than 15 cm with some thicker ice
8 Ice predominantly grey–white (15-30 cm thick) with some ice thicker than 30 cm
9 Ice predominantly thicker than 30 cm with some thinner ice
/ No information or unable to report

TB Topography or form of ice

0 Pancake ice, ice cakes, brash ice -less than 20 m across
1 Small ice floes - 20 - 100 m across
2 Medium ice floes - 100 - 500 m across
3 Big ice floes - 500 - 2000 m across
4 Vast or giant ice floes or level ice - more than 2000 m across
5 Rafted ice
6 Compacted slush or shuga, or compacted brash ice
7 Hummocked or ridged ice
8 Thaw holes or many puddles on the ice
9 Rotten ice
/ No information or unable to report

KB Navigation conditions in ice

0 Navigation unobstructed
1 Navigation difficult or dangerous for wooden vessels without ice sheathing.
2 Navigation difficult for unstrengthened or low-powered vessels built on iron or steel.
Navigation for wooden vessels even with ice sheathing not advisable.
3 Navigation without icebreaker assistance possible only for high-powered vessels
of strong construction and suitable for navigation in ice.
4 Navigation proceeds in lead or broken ice-channel without the assistance of an icebreaker.
5 Icebreaker assistance can only be given to vessels suitable for navigation in ice and of special size.
6 Icebreaker assistance can only be given to vessels of special ice class and of special size.
7 Icebreaker assistance can only be given to vessels after special permission.
8 Navigation temporarily closed.
9 Navigation has ceased.
/ Unknown


Koslowski, G., 1981: Der Ostsee-Eiskode von 1980. (Seewart 42, 176-184)
Swedish Meteorological and Hydrological Institut, 1981: The Baltic Sea Ice Code, Norrköping, 42
WMO, 1970: WMO Sea-Ice Nomenclature. WMO/OMM/BMO, Geneva No.259. TP. 145