Only one day left of October as we continue to march closer to the winter season for Iowa. Besides the obvious difference with colder temperatures during the season, there is also a marked difference to the number of days with low overcast clouds. The featured chart depicts a histogram of overcast cloud conditions by week of the year and level they are reported at by the automated sensor at the Ames Airport. The coldest part of the year sees the highest frequency of having low overcast clouds. The decreasing solar incidence angle and shortening daylight time conspire to allow less depth of mixing of the lower atmosphere. The colder temperatures are also quicker to saturate and create clouds. You may notice the rapid increase at 5 thousand feet AGL, this is an artifact of how the sensor and observation reporting works. The sensor is also capped with how high up it is able to sense clouds.

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