Major Blackout Affects Wyoming And Western South Dakota

A widespread power outage swept across multiple states Thursday, cutting electricity to an estimated 95,000 Wyoming customers and possibly sparking a fire at the Dave Johnston coal-fired power plant near Glenrock.

The blackout affected more than 10% of Wyoming utility customers and stretched into western South Dakota. According to the Western Area Power Administration, the disruption began around 12:45 p.m. when two major 500-kilovolt transmission lines near Medicine Bow tripped, triggering an abnormal voltage event that cascaded across the regional grid and shut down additional lines.

By 4:30 p.m., about half of those affected had power restored, though officials warned the system remained unstable. Multiple utilities were impacted — including Rocky Mountain Power, Black Hills Energy and Montana-Dakota Utilities — an unusual scenario that underscored the scale of the grid disturbance.

The Dave Johnston power plant fire began after the outage, state homeland security officials said, emphasizing that the blaze appeared to be a consequence of the grid failure, not the source of it. Local emergency officials reported the fire had been extinguished by midafternoon.

Communities including Gillette, Casper, Douglas, Newcastle and Sheridan experienced significant disruptions, with Natrona County seeing the highest number of outages. Rocky Mountain Power reported more than 56,000 customers without electricity, while Powder River Energy Corporation logged more than 26,000 impacted meters. Some towns dealt with flickering or intermittent service as voltage levels fluctuated.

Powder River Energy urged residents to prepare for outages potentially lasting into the night, explaining that unstable voltages were causing power to repeatedly trip off. Utility crews were stationed at substations across the region, ready to safely restore power once conditions stabilized.

In Gillette and Casper, entire city grids went offline at points throughout the afternoon. Casper police directed residents who rely on oxygen to designated facilities. The Natrona County library, YMCA and several businesses closed early, and after-school activities were canceled as disruptions continued.