PSM V3 high humidity

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The relative humidity seems too high in the data I downloaded. I'm looking at 2016 data for the Philadelphia International Airport (here's the CSV filename "1204496_39.89_-75.26_2016.csv"). There are frequently relative humidities of 100%- even in the winter- and generally, the results don't seem the same when I do a quick comparison with weather underground. Could this be a mistake?
Thanks for your help,
Jeremy