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Interpreting Ice Charts

World Meteorological Organization Colour Code

Experts have long considered including colour coding for sea-ice charts in the World Meteorological Organization's "Sea Ice Nomenclature", but until recently this was considered optional.

However, the widespread use of electronic navigational information systems has brought about a definite need for colour coding on sea-ice charts. As a result, during the 2000-2001 period the International Ice Charting Working Group (International Ice Charting Working Group) prepared a draft colour standard consisting of two mutually exclusive colour codes based on:

  • total concentration; and
  • stage of development.

These proposed codes complement the existing World Meteorological Organization black and white ice symbols and are designed to be flexible.

Keys to Using and Understanding the World Meteorological Organization Colour Codes

There are two colour codes for use on sea-ice charts. They are based on:

  • total concentration: this code is used when concentration is highly variable but the stage of development is relatively uniform;
  • stage of development: this code is used when the stage of development is variable but the concentration is relatively uniform.

The two colour codes are mutually exclusive; only one should be used on a single chart.

  • Every chart should include a legend depicting the colour code used.
  • "Undefined Ice" is used when it is known that sea ice is in an area, but its characteristics are not known. This is different from "No Information", which indicates that nothing is known about the area.
  • No specific colour is assigned to areas of "No Information". Such areas should be clearly indicated on sea-ice charts-text annotation may be used where appropriate; an assigned colour within the code should not be used to indicate "No Information".
  • The use of colour codes does not rule out black and white hatching patterns or egg codes; egg codes may be used along with colours.
  • Other symbols may be used with the standard colours to depict special ice conditions under national practice.

Concentration Colour Code for Sea Ice

The World Meteorological Organization's colour code for total concentration is an international code that is intended for use when the stage of development is relatively uniform, but concentrations are highly variable (e.g. arctic summer). The legend for the use of the colour code is included on the chart. No colours are used to indicate differences in the ice stage of development.

World Meteorological Organization's Total Concentration Colour Code

Colour/
Pattern
Total concentration
 BlueIce free
 WhiteIce free (Used at CIS)
 Light blueLess than one tenth (open water)
 Light green1/10 - 3/10 (very open ice)
 Yellow4/10 - 6/10 (open ice)
 Orange7/10 - 8/10 (close ice)
 Red9/10 - 10/10 (very close ice)
 GreyFast ice
? ? ? ?
Undefined ice

Optional World Meteorological Organization's Total Concentration Colour Code

ColourTotal concentration
 Light pink7/10-10/10 new ice
 Pink9/10-10/10 nilas, grey ice (mainly on leads)

*Areas of "No Information" are annotated accordingly

 

Stage of Development Colour Code for Sea Ice

World Meteorological Organization's Stage of Development Colour Code

Colour/
Pattern
Stage of DevelopmentThickness
 BlueIce Free 
 WhiteIce free (Used at CIS) 
 Light blue< 1/10 Ice (Open Water) 
 Light purpleNew Ice< 10 centimetres
 PurpleGrey Ice10-15 centimetres
 PinkGrey-white Ice15-30 centimetres
 YellowFirst-year Ice>=30 centimetres
 Light greenThin First-year Ice30-70 centimetres
 GreenMedium First-year Ice70-120 centimetres
 Dark GreenThick First-year Ice> 120 centimetres
 Dark orangeOld Ice 
 OrangeSecond-year Ice 
 RedMulti-year Ice 
 GreyFast Ice of Unspecified Stage of Development 
? ? ? ?
Undefined Ice 
White with red triangle fill
Drifting Ice of Land Origin (icebergs) 

 

Note: The following stage of development colour codes are part of the World Meteorological Organization colour code standard but are not depicted on the Canadian Ice Service chart products.

 

Stage of Development Colour Code Standard for Sea Ice - Additional Codes

Colour
(prime)
Stage of Development (Stage of Development)Thickness
 Light pinkDark Nilas<=5 centimetres
 PinkLight Nilas> 5 centimetres
 PurpleYoung Ice10-30 centimetres
 Light greenThin First-year Ice (white ice); First Stage30-50 centimetres
 GreenThin First-year Ice (white ice); Second Stage50-70 centimetres

 

Concentration Colour Code for Lake Ice

World Meteorological Organization's Total Concentration Colour Code for Lake Ice

Colour/
Pattern
Description
 WhiteIce Free
 Light blueLess than one tenth (open water)
 Light green1/10 - 3/10 (very open ice)
 Yellow4/10 - 6/10 (open ice)
 Orange7/10 - 8/10 (close ice)
 Red9/10 - 10/10 (very close ice)
 GreyFast Ice of Unspecified Stage of Development
? ? ? ?
Undefined Ice

*Areas of "No Information" are annotated accordingly

 

Stage of Development Colour Code for Lake Ice

World Meteorological Organization's Stage of Development Colour Code for Lake Ice

Colour/
Pattern
Stage of DevelopmentThickness
 WhiteIce Free 
 Light blueIce of Unspecified Stage of Development (open water) 
 Light purpleNew Lake Ice< 5 centimetres
 PurpleThin Lake Ice5-15 centimetres
 PinkMedium Lake Ice15-30 centimetres
 Light greenThick Lake Ice30-70 centimetres
 GreenVery Thick Lake Ice> 70 centimetres
 GreyFast Ice of Unspecified Stage of Development 
? ? ? ?
Undefined Ice 
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