The past few mornings have featured strong "radiational cooling" events thanks to clear skies and calm winds. Such events often highlight micro-climate differences between weather stations, which was the case when you compare temperatures at the Ames airport vs Des Moines. Temperature differences between the two stations reached 8°F during the morning hours. A daily feature last week highlighted the Des Moines heat island, which tends to buoy temperatures at night time. So with the Ames station being much less urban, it stands to reason that large temperature differences could happen when the heat island effect is most pronounced. The featured chart takes a bit of a deep dive into air temperature differences between the two sites. The top left panel shows the raw values so far this July. The top right panel presents the frequency of Ames being warmer by hour and week of the year. The bottom left panel shows yearly aggregate statistics. The bottom right panel partitions the data by month of the year. Perhaps the most interesting sub-plot is the upper right, which shows two clear areas of increased frequency of Ames being warmer than Des Moines. The reason for these two likely has to do with increased humidity levels due to nearby cropping increasing morning temperatures during the growing season and then a sandier soil allowing for increased heating during the day vs Des Moines.

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