Weekly Ice Cover Statistics (1973-2002)

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 1-7; the Dec 2 grid is Dec 2-8. 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): ftp://ftp.glerl.noaa.gov/publications/tech_reports/glerl-133/ .

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.
Ice Codes -1 = land grid cell, 0 to 100 = the percentage of a grid cell covered by ice.

Maximum (largest observed ice concentration)
Computer Animation: AVI format | FLC format
ASCII Grid Files: maxgrid30.zip
Graphic Files: maxplotpng30.zip
Preview Selected Graphic Files at Weekly Intervals

Median (the 50% point in the frequency distribution)
Computer Animation: AVI format | FLC format
ASCII Grid Files: medgrid30.zip
Graphic Files: medplotpng30.zip
Preview Selected Graphic Files at Weekly Intervals

Minimum (smallest observed ice concentration)
Computer Animation: AVI format | FLC format
ASCII Grid Files: mingrid30.zip
Graphic Files: minplotpng30.zip
Preview Selected Graphic Files at Weekly Intervals

First Quartile (the 25% point in the frequency distribution)
Computer Animation: AVI format | FLC format
ASCII Grid Files: q1grid30.zip
Graphic Files: q1plotpng30.zip
Preview Selected Graphic Files at Weekly Intervals

Standard Deviation (variation about the mean)
Computer Animation: AVI format | FLC format
ASCII Grid Files: stdgrid30.zip
Graphic Files: stdplotpng30.zip
Preview Selected Graphic Files at Weekly Intervals

Synoptic Median (the observed ice chart for a given week over the 30-winter base period that is most similar to the statistical median ice chart for each Great Lake)
Computer Animation: AVI format | FLC format
ASCII Grid Files*: synmedgrid30.zip
Graphic Files: synmedplotpng30.zip
Preview Selected Graphic Files at Weekly Intervals

* These files have 4 header records that give the date of the synoptic median for each lake:
1. “Synoptic Median Charts by Lake”
2. “ E H M O S “
3. “ yyddd yyddd yyddd yyddd yyddd “
4. (intentionally left blank)

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
Weekly Ice Cover Statistics | Contact

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