It was -37 at the time, and temperatures would reach nearly -40 before power was completely restored around 7 p.m.
The Northwest Territories Power Company hasn't yet confirmed what caused the crash.
Power came back up in parts of Yellowknife by 5:45 p.m. but went out again as the power corporation tried to bring all of the feeders out of the Jackfish Lake substation online. All but one of the 20 feeders was back up by about 6:45, but one of the large ones to Yellowknife continued to cause problems. Worried it would crash the grid again, the final circuit was splits into two feeders so it could be brought online gradually.
All customers had power restored by 6:55 p.m.
The CBC is expecting more details about the failure from a spokesperson for Northwest Territories Power Corporation later this morning.
Meanwhile, the power outage caused a lot of buzz online, as Yellowknifers turned to social media to find out what was going on.