Actually not positive what exact mechanism is used... I tell the program which specific weather station to use, and then each GPS track I import, I can also tell it to retrieve the associated weather data (that is, for the same time period as my gps track). Then I can view a graph of temp, humidity, precip, pressure, wind speed data against the corresponding gps track.
If I have a chance, I'll add a screenshot this week to show you what I mean.
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