Tuesday's winter wonderland in Southeast Texas is taking on a new, uglier form thanks to an overnight hard freeze rendering roads and walkways treacherously slick.  Snow melt from Winter Storm Enzo, which dropped more than 5 inches of snow in isolated areas around Houston,

Drivers are urged to exercise caution during their morning commutes as black ice may have reformed in isolated spots on Houston roadways overnight. Drivers should look for any wet surfaces, as they can be icy.

Black ice is an invisible cold weather danger, but how does it form and how can you protect yourself when walking and driving?