Phasor measurement units (PMUs) allow voltage angle differences across power grids to be monitored to identify sudden shifts associated with system disturbances. The Eastern Interconnection Situational Awareness and Monitoring System (ESAMS) was developed to identify such wide-area disturbances and summarize them in reports released the following day. Demonstration of ESAMS in North America’s Eastern Interconnection revealed the need for an effective visual summary of the disturbance’s impact on voltage angle pairs. This paper proposes the use of the circular variance, a measure of dispersion applicable to angular data, for this purpose. Results based on PMU data from North America’s Eastern and Western interconnections indicate that the circular variance provides useful summaries of wide-area voltage angle measurements. They also show that the circular variance may have potential uses when applied to historical data to identify unusual grid conditions.