TC Energy’s 590,000-bbl/d Keystone oil pipeline resumed operations on Jan. 5, the company said, after it was shut the previous evening for unplanned maintenance as parts of western Canada grappled with frigid winter weather.

TC said the pipeline, which ships crude from the oil sands province of Alberta to the U.S. Midwest, was restarted safely at around 6:15 p.m. local time on Jan. 5 amid extremely cold temperatures at its Hardisty terminal in central Alberta.

Temperatures in Hardisty were forecast to plunge to minus 35 C (minus 31 F) the night of Jan. 5. Most of Alberta is under an extreme cold warning that is expected to last until the weekend.

The company said the unplanned maintenance on Keystone began at around 8 p.m. local time on Jan. 4. TC’s Gulf Coast operations in the U.S. were uninterrupted.

Canadian heavy crude prices tightened on Jan. 4 as traders anticipated oil sands production issues relating to the cold snap. On Jan. 5, Western Canada Select heavy blend crude traded at $12.10/bbl below the U.S. crude benchmark, narrowing 5 cents from the previous day.