With a strong surface high pressure system overhead, temperatures cooled nicely on Wednesday morning with most of the state experiencing the first freeze of the fall season. The Ames airport bottomed out to 24°F! The featured chart presents a time series of Ames airport cloud coverage reports for a +/- 24 hour period relative to the first fall sub 29°F reading. Each pixel represents an hourly report with tan values indicating missing data. It is very interesting and intuitive to see the lack of cloud cover near the occurrence of such a cold temperature. It is a testament to the importance of radiational cooling for such events as clouds act as the proverbial blanket to buoy near surface air temperatures during night time hours.

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Tags:   firstfreeze   clouds