"It's called 'black ice' because it tends to look like the rest of the pavement on the road, although in reality, it's actually clear," the US Forest Service notes. "Black ice forms without creating bubbles, which allows it to blend in with any surface it forms over. Black ice is dangerous precisely because it's hard to detect."

While temperatures will warm up by mid-morning, refreezing remains a concern, particularly north of the Metroplex.

Residents across parts of the Gulf Coast and South are bracing for a rare winter storm expected to drop heavy snow and create treacherous conditions.

Hazardous travel conditions are expected early Tuesday across the San Antonio metro area, but snow and ice will likely melt by the afternoon.