The featured chart takes a look at the impact of having clear skies on air temperature by comparing hourly weather reports at Des Moines over its archive since 1973. The data is partitioned by week of the year to remove some variability. Each pixel represents the average temperature difference between clear sky conditions vs all available reports. A positive value means the air temperatures are warmer than overall. The chart shows a clear annual and diurnal signal. During the overnight hours, clear skies allow for more radiational cooling, so temperatures are cooler. During the day, the lack of clouds allows for more heating, but this effect is muted during the winter months due to the presence of snow and the general lack of significant solar energy incident during this season.

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