Relative Humidity Lab

Here is a map of where we collected relative humidity data today using slide psychrometers. It was a fun day. Each placemark on this map displays the average relative humidity from data collected during 3rd, 4th, 6th, and 8th Periods.

View Relative Humidity Lab in a larger map
Overall, the average humidity outside was 73%. All relative humidities taken inside the building were averaged as well, and the result was 68%.
The relative humidity according to the National Weather Service was 45% this afternoon. What could have caused the discrepancy? Why do you think our humidity values were higher?