Chilly overnight low temperatures have been elusive so far this October, but that looks to change over the next few days thanks to less humid air and clear overnight skies. Having warmer low temperatures during October has been somewhat of a trend over the past number of years. The featured chart presents the frequency distribution of October daily low temperatures for Des Moines during two sequential 30 year periods. The distribution is smoothed to filter out some of the noise with the two 30 year periods overlain and then differenced via the bottom chart. The most recent period has seen a slight shift in distribution with more frequent days in the 40s vs the 30s. The y-axis units are a bit hard to explain, but the larger the number indicates more frequent events. The right hand table presents the percentiles for each period with about a one degree difference shown.

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