Yesterday's feature looked at the afternoon dew point being an indicator of the next day's low temperature. The theory being that the air temperature would cool off to the dew point temperature and thus be the low temperature. Today's feature looks at the distribution of dewpoint depression at the time of the daily low temperature for each of the ASOS sites in the state. The dewpoint depression is simply the difference between the air and dewpoint temperature. Differences between sites are likely due to micro-climate effects as each ASOS has different surroundings which include soil types, vegetation, and amount of urban area / concrete around it. The chart shows a large difference between Ames and Des Moines with the median dewpoint depression two degrees less at Ames. The first guess explanation for this difference is the larger urban heat island effect at Des Moines, which would tend to keep the temperature higher and further away from the dewpoint than surrounding locations. Also, the Ames ASOS is located in a topographic depression which would promote cooler temperatures.

Additional plots: same plot for high temperatures, Ames weekly dewpoint depression, and weekly for Des Moines.

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Tags:   dewpoint   asos   heatisland