Great Lakes Ice Charts


Charts show ice extent and concentration three times weekly during the ice season, for all lakes except Ontario, from the 1973/74 ice season through the 2001/2002 ice season. Most charts are annotated to indicate data sources. Straits of Mackinac, Green Bay and Sault Ste. Marie are enlarged as insets, and in some cases, provided as separate charts. From 1973/74 through 1986/87, charts were prepared by the National Weather Service Forecast Office, Ann Arbor, Michigan. Beginning with the 1987/88 season, the National Ice Center (formerly known as the Navy/NOAA Joint Ice Center) in Suitland, Maryland prepared the charts. Charts are available as GIF files.

File Naming Convention

On the FTP site, the GIF files for each melt season are tarred together into one file of the form yy1_yy2.tar where yy1 is the 2-digit year of the beginning year of the melt season and yy2 is the 2-digit year of the end of the melt season.

The data files within the tar files are named according to the following convention. Note: Starting in 2000, some images are supplied as jpg instead of gif.



Variable Description
xx[x] 2-3 digit location code:

cis: All great lakes
el: Eastern Great Lakes including Lake Erie, Lake Huron, Georgian Bay, and North Channel
gbl: Green Bay
gl: All great lakes
ml: Whitefish Bay south to Detour, including Sault Ste. Marie and St. Mary's River south to Detour, Michigan
scr: St. Clair River
wl: Western Great Lakes including Lake Michigan and Superior

Note: Prior to the 1986-87 ice season, charts were organized by region. Beginning with the 1986-87 ice season and beyond, all regions were combined into a single chart for each date. Each chart then has a "gl" prefix in the file name to indicate "all" Great Lakes.
yy 2-digit year
mm 2-digit month
dd 2-digit day of month


Note: For the 01-02 melt season, ASCII text files of descriptions of the ice are provided as well as GIS .e00 files.

Access Data

The data are available via FTP.


This data collection is being provided as is. NOAA@NSIDC believes these data to be of value but is unable to provide more complete documentation.

Data Citation

National Snow and Ice Data Center, compiler. 1995. Great Lakes ice charts. Boulder, CO: National Snow and Ice Data Center.