Very cool overnight temperatures visited the state this past weekend with lows approaching freezing over northwestern Iowa on Saturday morning. This very cool weather was close to the most recent full moon late last week. There is a saying in weather folklore that the first freeze of the fall season often happens on the full moon as having a full moon impacts the profile of water vapor which allows temperatures to more rapidly cool. The featured chart looks at the first fall sub 29 degree temperature for Ames and the proximity to the nearest full moon. As you can clearly see, these events happen at about any time during the lunar cycle. The reason that this folklore gets perpetuated is that the first frost is almost always on a clear sky night with limited water vapor in the air, so any moon will appear very bright and crisp.

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Tags:   moon   folklore