Hi! Yea I'm not too far from the airport but finally got my own weather station so I can now compare my info to Dulles since I am usually a degree or 2 warmer than the airport.
You can also see real time IAD flight weather data on this link: http://www.iadasos.org/IAD/index.html. very helpful as it updates every minute.
Down to 38.8/19.8