

Weekly Ice Cover Statistics (19732002)Maximum  Median  Minimum  First Quartile  Third Quartile  Std Deviation  Synoptic Median Introduction There are 173 weekly grid files and 173 weekly plot files for each of seven statistics. Each statistic is given in a compressed .zip file. The 173 files start Dec1 and end May 22. Each weekly grid overlaps its predecessor by six days, for example, the Dec1 gird is Dec 17; the Dec 2 grid is Dec 28. Thus, for any day in winter there are weekly statistics. Computer animations (AVI or FLC formats) portray the changing spatial pattern of each statistic over the winter. Data and methods used to calculate weekly ice cover statistics, spatial distribution patterns of the weekly statistics, anomaly ice charts, and mild and severe winters are presented and discussed in Assel (2005): http://www.glerl.noaa.gov/ftp/publications/tech_reports/glerl133/ . Grid Format Each grid file contains 510 records. Each
record had 516 fields in a fixed I3 format. The synoptic median grid files
have 4 records that precede the 510 data records. Maximum (largest observed ice concentration) Median (the 50% point in the frequency distribution) Minimum (smallest observed ice concentration) First Quartile (the 25% point in the frequency
distribution) Third Quartile (the 75% point in the frequency distribution) Computer Animation: AVI format  FLC format ASCII Grid Files: q3grid30.zip Graphic Files: q3plotpng30.zip Preview Selected Graphic Files at Weekly Intervals Standard Deviation (variation about the mean) Synoptic Median (the observed ice chart for
a given week over the 30winter base period that is most similar to the
statistical median ice chart for each Great Lake) * These files have 4 header records that give the date of the synoptic
median for each lake: Where: E = L. Erie, H = L. Huron, M = L. Michigan, O = L. Ontario, S
= L. Superior, yy = year (73 = 1973, 74 = 1974…02 = 2002), and ddd
= day of season (101= Dec. 1, 102 = Dec. 2,… 282 = May 30 or May
31). 

Introduction  Original
Ice Charts  First Ice,
Last Ice & Ice Duration  Daily
Ice Cover Time Series
US Department of Commerce
 NOAA  OAR
 GLERL
