Tripped High-Voltage Lines Knock Out Power for Thousands Across Wyoming

County 10, WyoFile, Oil City News, Wyoming Public Media, and Casper Star Tribune contributed to this report.

A massive power outage rippled across Wyoming on Thursday, cutting electricity to as many as 95,000 customers and briefly sparking a fire at the Dave Johnston coal-fired power plant near Glenrock, officials said.

The blackout started just before 1 p.m. and hit more than 10% of the state’s electric customers, spilling over into parts of western South Dakota. What made it especially unusual is that it didn’t just knock out one utility — it hit several at once, including Rocky Mountain Power, Black Hills Energy, Montana-Dakota Utilities and multiple rural electric co-ops that all share the same regional grid.

Federal grid managers say the trouble started near Medicine Bow. Stephen Collier, public affairs specialist for the Western Area Power Administration, said two 500-kilovolt transmission lines tripped around 12:45 p.m. That triggered what he called an “abnormal voltage event,” which then cascaded across the system and shut down other lines, including WAPA’s own transmission. The result: communities from Casper to Gillette and beyond suddenly went dark.

By about 4:30 p.m., roughly half of the affected customers had power again, according to outage trackers, but grid operators warned that the system could remain shaky into the night. Many people reported the lights popping on and off repeatedly as utilities tried to stabilize voltages and bring areas back online in stages. Powder River Energy Corporation told members to be ready for a long haul, explaining that low, unstable voltages were “tripping off power” and that crews were parked at substations waiting for things to settle before flipping anything back on.

The outage appears to have triggered secondary problems, including a fire at the Dave Johnston power plant east of Glenrock. Converse County emergency officials said the fire broke out after the blackout began and was quickly brought under control with help from outside crews. The Wyoming Office of Homeland Security stressed that the plant fire was likely a consequence of the outage, not the cause of it. A separate plume of black smoke from the Steamboat Gas Plant near Douglas was attributed to that facility losing power as well, and was not considered an emergency.

Communities across central and northeast Wyoming felt the impact. Gillette reported a citywide outage around 12:40 p.m., briefly restored service, then lost it again less than an hour later. Casper police said the city’s outage appeared to be system-wide at one point, prompting officials to direct oxygen-dependent residents to designated locations with backup power, including facilities at Natrona County High School and Banner’s east campus. Natrona County’s library, YMCA and many local businesses shut their doors early. County offices and several Casper city facilities — including City Hall, the recreation center, ice arena, family aquatic center and Fort Caspar — closed for the remainder of the day out of safety concerns.

In Douglas, Glendo, Riverton, Buffalo, Glenrock and other communities, residents and businesses reported flickering lights, dead intersections and forced closures. Some liquor stores and shops in Glenrock taped handwritten notes on their doors explaining they were closed because of the outage, just a few miles from the coal plant that normally helps keep the region powered. Rural co-ops from High Plains Power to Niobrara Electric and Wyrulec all reported transmission-related outages and warned customers that restoration would be slow and deliberate to avoid damaging transformers and other equipment.

With so many lines down at once, emergency managers urged people to treat every downed wire as live and to stay away, to avoid overloading circuits when the power came back, and to check on elderly neighbors or anyone who relies on electricity for medical equipment. Those who needed to charge oxygen machines or other life-sustaining devices were told to contact local emergency management offices or head to designated charging locations in Douglas, Glenrock and Casper.

As utilities continue to piece the grid back together, state and federal officials are digging into how two tripped high-voltage lines near Medicine Bow managed to knock out power across such a wide swath of Wyoming — and briefly set a coal plant on fire — on an otherwise ordinary Thursday afternoon.