Past IEM Features tagged: moon
You ask most any old timer and they'll tell you that one needs to worry about frost on the first full moon during late September or October. The reason for this belief ranges from moon's gravity pulling humidity / clouds away allowing more rapid cooling or perhaps the moon helping to cool the atmosphere itself somehow, anyway. We just got past a full moon last weekend without a freeze, so perhaps we should worry when the next full moon comes around (more on this date later). The featured chart shows rather clearly that there isn't much of a relationship between the first fall sub 32 degree temperature for Ames and the number of days to the closest full moon date. What is interesting though is that the overall date average on this plot is around 9 October and you can likely guess when our next full moon is scheduled! Lock it in now? We certainly will have to wait at least a week or two more as temperatures look quite hot for the foreseeable future.
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.
Tags: moon folklore
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IEM tracked NWS COOP sites used for this analysis
It is commonly said that the first fall season freeze occurs during a full moon in late September or October. The featured plot shows that this simply is not the case in Iowa. The horizontal axis contains the number of days from the nearest full moon and the vertical axis is the number of days that observation was from the 6th of October (the median first freeze date). The contours indicate the relative frequency of the data. The important portion of the plot is the histogram in red at the top of the page clearly showing no full moon date dependence. Here is an Excel file with this data.
Tags: climate moon freeze
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Picture taken by Gayle Ferguson of Van Meter
The authoritative source of knowledge, wikipedia, says that the Harvest Moon is the full moon closest in time to the fall equinox (beginning of fall). The authoritative source of weather forecasting, the Farmer's Almanac, notes that the Harvest Moon helps farmers harvest at night and lets then know that their crops are mature. Regardless, it was a very pretty moon rise last night.