Up to 95,000 customers experienced a massive power outage on Thursday afternoon, sweeping across central and north-eastern Wyoming. The outage rippled across several counties, including neighboring state South Dakota.
A Federal Western Area Power Administration (WAPA) spokesperson said that the blackout began around 12:45pm (local time) and was 'triggered by two tripped 500-kilovolt lines near Medicine Bow, Wyoming.'
The abnormal voltage event apparently cascaded, causing multiple transmission lines to trip and triggering widespread outages across several utilities.
The outage spanned multiple counties and affected a number of cities. Among the hardest hit were the city of Casper, Wyoming, and towns such as Gillette, as well as other communities, including Douglas, Newcastle, and Sheridan.
At one point, Rocky Mountain Power (RMP) listed more than 55,000 customers without power. Meanwhile, the rural co-op Powder River Energy Corporation said that 26,544 of its members experienced outages.
The City Police Department of Casper has issued guidance for residents who are oxygen dependent or in life-sustaining equipment to seek help at two designated locations.
Firefighters have also responded to alarms in the Casper Business Center shortly after the power was gone. The alarm was triggered by smoke caused by the generators used for the outage.
Many local businesses and public offices closed early; the Natrona County library and YMCA were reported to have shut for the rest of the day.
Origin of the Power Outage
While the immediate cause is understood to be the tripping of two 500 kV lines near Medicine Bow, the wider ramifications remain under investigation.
WAPA's Stephen J. Collier said, 'We believe the outage was triggered by two tripped 500-kilovolt lines near Medicine Bow.
This incident resulted in an abnormal voltage event that subsequently tripped several surrounding lines, including WAPA transmission, resulting in further power outages to communities across the area.'
It is also noted that the fire at the Dave Johnston Power Plant near Glenrock occurred after the outage began and was considered a possible consequence rather than the cause.
The fact that multiple utilities were impacted, including RMP, Black Hills Energy, and rural co-ops, emphasises the interconnected nature of the transmission system and how a fault in one area can ripple across a wide region.
Restoration Efforts
By mid-afternoon, crews had begun restoring power, and by about 4:30pm, roughly half of the affected customers had electricity again. Officials cautioned, however, that conditions across the grid remained unstable, and further outages were still possible.
One rural co-op noted that safe restoration depended on voltage stabilising, saying, 'We do not want to flip the switches unsafely. We do not want to blow up transformers or arrestors and cause more problems.'
Smaller utilities, including Wyrulec Company in south-eastern Wyoming, reported that all their members had power restored, though brief fluctuations could still occur as the wider system settled.
However, larger regions in the north-east of the state remained slower to recover, particularly in rural counties, where crews had to navigate distance and sensitive equipment.
Officials urged residents to remain patient, warning that isolated interruptions could continue even after most communities regained service.
