This paper addresses the real-time use of ambient wet bulb temperature measurements in the optimization of building air conditioning system control as a means to save energy. This is not currently a common industry practice due to the maintenance requirements and perceived unreliability of humidity sensors. However, research shows that ambient wet bulb temperature is of central importance in determining optimal supervisory control of these systems. Since the UCSD campus operates its own weather stations, a case study was performed here as a first step in the implementation of their use in campus building control