How is the average temperature for a week calculated? And how many years back are used in figuring the average?

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Dear Tom,
How is the average temperature for a week calculated? And how many years back are used in figuring the average?
Matt Engel
Dear Matt,
A weekly average temperature, like average temperatures for other periods of time, is calculated by determining the arithmetic average temperature using the daily highs and lows for each of the seven days in that week.
The calculation for one week is as follows: Add up the seven daily highs and the seven daily lows, and then divide the sum by the number of entries, 14 in this case. For a year, we would sum up all the 365 daily highs and 365 daily lows (or 366 daily temperatures, if it’s a leap year), then divide the total by 730 (or 732).
Long-term averages (what are considered to be the climatological normals) are calculated from a 30-year base period currently using temperature data from 1981 to 2010.

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