Challenge Question #4

Jeanne Monteau (jmonteau@albany.net)
Sun, 22 Mar 1998 13:27:08 -0500

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I gave this challenge question to a number of students. It was
interesting to see the various strategies used and conclusions reached.
Clare and her Dad made a graph showing the number of days between
January 1 and 'ice-out' for each year and noted the the strong and very
strong El Nino years.

1. Based on the moving average, they conclude that ice-out will occur on
Lake Minnetonka approximately 105 days past Jan. 1, or on April 16,
1998. Many other students using different methods reached the same
conclusion.

2. Some El Nino years had late ice-out days and some had early ice-out
days. It may be that El Nino does not have an effect on places so far
north.

3. From 1948 to 1984, the average ice-out date was greater that the
average of all years (102.5). We had a long stretch of colder weather
from 1948 to 1984. From 1903 to 1913, and from 1926 to 1934, the
average ice-out days were less (warmer) than the average of all years.
We just finished a short stretch of warm weather from 1985 to 1993 but
the average is getting longer (colder).

4. The graph does not show a clear indication of global warming.

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