power outages can result from seasonal storms which often combine the furies of wind, rain, snow or ice. The more severe weather events usually cause the greatest damage to electric power transmission and distribution infrastructure as damage can result from trees or branches falling on electricity lines. While data on storm-related power outages exists, they are not generally considered to be complete or well characterized with regard to the cause of the outage event. It has been estimated that 90% of customer outage-minutes are due to events which affect local distribution systems. However, the remaining 10% stem from generation and transmission problems, which can cause wider-scale outages affecting larger numbers of customers.
According to the Vermont study, almost 44% of the events in the period were weather-related (i.e., caused by tornado, hurricane/tropical storm, ice storm, lightning, wind/rain, or other cold weather). The study noted that the data include many events smaller than the NERC reporting threshold. It also noted that some of the reported events have “multiple initiating” causes, since some events (such as lightning) can trigger other outages or operator errors.
Power outages caused by storm-related events can vary in duration but tend to be sustained disruptions. The study noted that weather-related events are not always captured in power outage data.