We have somehow made it to October and so looking back at September seems appropriate. The featured chart presents the combination of precipitation and growing degree day departures each September for Ames. The departures are expressed in terms of sigma which helps to normalize a comparison between variables having different units. This year came in at about average for precipitation and below average for GDDs. A linear trend is fit to the data and shows no relationship between these two variables, so September precipitation and GDDs tend to be independent.

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