The featured chart look into the daily variability of high temperature for Des Moines based on period of record data. The top panel displays the spread of daily high temperatures expressed in standard deviation for a given day and for the day to day variability. The plot shows that this time of year has some of the highest spread for temperature (most variability). The bottom panel just presents a diagnostic looking at the relationship between the two variabilities plotted. The moral of the story is that the previous day's high temperature is a better predictor of the current days high than the average for the date.

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