That's as clear as mud. What does a -20 vs. a 20 mean? That it was colder at noon than at midnight?
Assuming that there was some sensible definition (e.g. deviation from the past mean temperature, which is not at all what was stated) then "average deviation" has two obvious interpretations. Re-labeling "standard deviation" or "mean deviation" would not be helpful in this case, and the -20 and 20 values STILL don't help the case.
The article isn't clear but the deviation is either from the sample mean or the mean of the underlying random variable. You are trying to find the expected difference from the average and hence the absolute value(otherwise, the positive and negative deviations cancel out).
Assuming that there was some sensible definition (e.g. deviation from the past mean temperature, which is not at all what was stated) then "average deviation" has two obvious interpretations. Re-labeling "standard deviation" or "mean deviation" would not be helpful in this case, and the -20 and 20 values STILL don't help the case.